BSC 2023 Glossary

Sudden Infant Death Syndrome (SIDS)

A disorder resulting in the unexpected death during sleep of infants, usually between the ages of two weeks and one year. The causes are not fully understood, but are believed to involve failure of automatic respiratory control.

Morph

A distinct phenotypic variant within a population.

Endosperm

A food storage tissue that provides nutrients to the developing embryo in angiosperms; formed from the triploid cell produced when a sperm cell fertilizes the central cell. Some endosperm is solid (as in corn), some is liquid (as in coconut).

Extracellular Digestion

A form of digestion found in annelids, crustaceans, and chordates including vertebrates; takes place within the lumen of the digestive system, and the resulting nutrient molecules are transferred into the blood or body fluid.

Node of Ranvier

A gap between two of the Schwann cells that make up an axon's myelin sheath; serves as a point for generating a nerve impulse.

Ethylene

A gaseous plant hormone that stimulates fruit ripening and the dropping of leaves.

Mesoglea

A gel-like matrix that occurs between the outer and inner epithelial layers in cnidarians.

Severe Combined Immunodeficiency (SCID)

A genetic disorder in which afflicted individuals have no functional immune system and are prone to infections. Both the cell-mediated immune response and the antibody-mediated response are absent.

Lactose Intolerance

A genetic trait characterized by the absence of the enzyme lactase, which breaks down lactose, the main sugar in milk and other dairy products.

Pancreas

A gland in the abdominal cavity that secretes digestive enzymes into the small intestine and also secretes the hormones insulin and glucagon into the blood, where they regulate blood glucose levels. A digestive organ that produces trypsin, chymotrypsin and other enzymes as a pancreatic juice, but which also has endocrine functions in the production of the hormones somatostatin, insulin, and glucagon.

Prostate Gland

A gland that is located near and empties into the urethra; produces a secretion that enhances sperm viability. Gland is involved in the reproductive system in males, the prostate secretes a sperm activating chemical into the semen during the arousal/ejaculation response.

Halophiles

A group of archaebacteria that are able to tolerate high salt concentrations.

Sex Hormones

A group of steroid hormones produced by the adrenal cortex. Hormones that are produced in the gonads and promoted development and maintainence of the secondary sex characteristics and structures, prepare the female for pregnancy, and aid in development of gametes. Males produce testosterone, while females produce estrogen and progesterone.

Exoskeleton

A hard, jointed, external covering that encloses the muscles and organs of an organism; typical of many arthropods including insects.

Restriction Fragment Length Polymorphism (RFLP)

A heritable difference in DNA fragment length and fragment number; passed from generation to generation in a codominant way.

Larynx

A hollow structure at the beginning of the trachea. The vocal cords extend across the opening of the larynx.

Bladder

A hollow, distensible organ with muscular walls that stores urine and expels it through the urethra.

Lymphatic System

A network of glands and vessels that drain interstitial fluid from body tissues and return it to the circulatory system.

Endoplasmic Reticulum (ER)

A network of membranous tubules in the cytoplasm of a cell; involved in the production of phospholipids, proteins, and other functions. Rough ER is studded with ribosomes; smooth ER is not.

Abscisic Acid

A plant hormone that promotes dormancy in perennial plants and causes rapid closure of leaf stomata when a leaf begins to wilt.

Nastic Movement

A plant's response to a stimulus in which the direction of the response is independent of the direction of the stimulus. Non-directional plant movements.

Lignin

A polymer in the secondary cell wall of woody plant cells that helps to strengthen and stiffen the wall; related term lignified.

Chitin

A polysaccharide contained in fungi; also forms part of the hard outer covering of insects.

Cellulose

A polysaccharide that is composed of unbranched chains of glucose; the major structural carbohydrate of plants, insoluble in water, and indigestible in the human intestine.

Hepatitis B

A potentially serious viral disease that affects the liver; can be transmitted through sexual contact or through contact with infected blood.

Vaccine

A preparation containing dead or weakened pathogens that when injected into the body elicit an immune response.

Tap Root

A primary root that grows vertically downward and gives off small lateral roots; occurs in dicots. Root system in plants characterized by one root longer than the other roots.

Eutrophication

A process by which nutrients, particularly phosphorus and nitrogen, become highly concentrated in a body of water, leading to increased growth of organisms such as algae.

Exocytosis

A process by which the contents of a cell vacuole are released to the exterior through fusion of the vacuole membrane with the cell membrane.

Disruptive Selection

A process of natural selection that favors individuals at both extremes of a phenotypic range.

Stabilizing Selection

A process of natural selection that tends to favor genotypic combinations that produce an intermediate phenotype; selection against the extremes in variation.

Directional Selection

A process of natural selection that tends to favor phenotypes at one extreme of the phenotypic range.

Cyclin

A protein found in the dividing cells of many organisms that acts as a control during cell division.

Endothermic

A reaction that gives off energy. The product is in a lower energy state than the reactants.

Inflammation

A reaction to the invasion of microorganisms through the skin or through the epithelial layers of the respiratory, digestive, or urinary system; characterized by four signs: redness, swelling, heat, and pain.

Exothermic

A reaction where the product is at a higher energy level than the reactants.

Cycle

A recurring sequence of events; e. g., the secretion of certain hormones at regular intervals.

Hemoglobin

A red pigment in red blood cells that can bind with oxygen and is largely responsible for the blood's oxygen-carrying capacity. Hemoglobin is composed of four polypeptide chains, two alpha (a) and two beta (b) chains.

Hypothalamus

A region in the brain beneath the thalamus; consists of many aggregations of nerve cells and controls a variety of autonomic functions aimed at maintaining homeostasis.

Sinoatrial (SA) Node

A region of modified muscle cells in the right atrium that sends timed impulses to the heart's other muscle cells, causing them to contract; the heart's pacemaker.

Sensory Cortex

A region of the brain associated with the parietal lobe.

Suprachiasmatic Nucleus (SCN)

A region of the hypothalamus that controls internal cycles of endocrine secretion.

Asthma

A respiratory disorder caused by allergies that constrict the bronchioles by inducing spasms in the muscles surrounding the lungs, by causing the bronchioles to swell, or by clogging the bronchioles with mucus.

Bronchitis

A respiratory disorder characterized by excess mucus production and swelling of the bronchioles; caused by long-term exposure to irritants such as cigarette smoke and air pollutants.

Reflex

A response to a stimulus that occurs without conscious effort; one of the simplest forms of behavior.

Motor Output

A response to the stimuli received by the nervous system. A signal is transmitted to organs that can convert the signals into action, such as movement or a change in heart rate.

Inversion

A reversal in the order of genes on a chromosome segment.

Action Potential

A reversal of the electrical potential in the plasma membrane of a neuron that occurs when a nerve cell is stimulated; caused by rapid changes in membrane permeability to sodium and potassium.

Gastroesophageal Sphincter

A ring of muscle at the junction of the esophagus and the stomach that remains closed except during swallowing to prevent the stomach contents from entering the esophagus.

Fruit

A ripened ovary wall produced from a flower.

Fibrous Root

A root system found in monocots in which branches develop from the adventitious roots, forming a system in which all roots are about the same size and length.

Nucleolus

A round or oval body in the nucleus of a eukaryotic cell; consists of DNA and RNA and produces ribosomal RNA (pl.: nucleoli).

Lymphatic Circulation

A secondary circulatory system that collects fluids from between the cells and returns it to the main circulatory system; the circulation of the lymphatic system, which is part of the immune system.

Codon

A sequence of three nucleotides in messenger RNA that codes for a single amino acid.

Grana

A series of stacked thylakoid disks containing chlorophyll; found in the inner membrane of chloroplasts.

Clitoris

A short shaft with a sensitive tip located where the labia minora meet; consists of erectile tissue and is important in female sexual arousal.

Pineal Gland

A small gland located between the cerebral hemispheres of the brain that secretes melatonin.

Second Messenger

A small, nonprotein, water-soluble molecule or ion, such as calcium ion or cyclic AMP, that relays a signal to a cell's interior in response to a signal received by a signal receptor protein.

Race

A subdivision of a species that is capable of interbreeding with other members of the species.

Ecotype

A subdivision of a species; a stage in the formation of a species such that reproductive isolation has occurred.

Compound

A substance formed by two or more elements combined in a fixed ratio.

PGAL (Phosphoglyceraldehyde)

A substance formed from PGA during the dark reaction of photosynthesis. Some PGAL leaves the cycle and can be converted to glucose, while other PGAL molecules are used to reform ribulose biphosphate (RuBP) to continue the dark reaction.

Pectin

A substance in the middle lamella that cements adjoining plant cells together.

Acid

A substance that increases the number of hydrogen ions in a solution.

Amensalism

A symbiotic relationship in which members of one population inhibit the growth of another population without being affected.

Sexual Reproduction

A system of reproduction in which two haploid sex cells (gametes) fuse to produce a diploid zygote.

Glomerulus

A tangle of capillaries that makes up part of the nephron; the site of filtration.

Cytoskeleton

A three-dimensional network of microtubules and filaments that provides internal support for the cells, anchors internal cell structures, and functions in cell movement and division.

Mass Extinction

A time during which extinction rates are generally accelerated so that more than 50% of all species then living become extinct; results in a marked decrease in the diversity of organisms. Mass extinctions are thought to have occurred numerous times in Earth history, often for a variety of reasons: impacts, tectonism, changes in primary productivity of the seas, etc.

Ecological Time

A timescale that focuses on community events that occur on the order of tens to hundreds of years.

Ozone

A triatomic (O3) form of oxygen that is formed in the stratosphere when sunlight strikes oxygen atoms. This atmospheric ozone helps filter radiation from the sun.

Unsaturated Fat

A triglyceride with double covalent bonds between some carbon atoms.

Neural Tube

A tube of ectoderm in the embryo that will form the spinal cord.

Nephron

A tubular structure that is the filtering unit of the kidney; consists of a glomerulus and renal tubule.

Macrophages

A type of white blood cell derived from monocytes that engulf invading antigenic molecules, viruses, and microorganisms and then display fragments of the antigen to activate helper T cells; ultimately stimulating the production of antibodies against the antigen.

Semilunar Valve

A valve between each ventricle of the heart and the artery connected to that ventricle.

Eyespot

1) A pigmented photoreceptor in euglenoids. The eyespot senses light and orients the cell for maximum rates of photosynthesis. 2) Term applied to a photosensitive area in starfish.

Medulla

1) A term referring to the central portion of certain organs; e.g., the medulla oblongata of the brain and the adrenal medulla, which synthesizes epinephrine and norepinephrine. 2) In more common usage, the area in the brain that regulates breathing, heartbeat, blood pressure and similar activities.

Budding

1) Asexual production of new organisms; usually found in yeast; 2) the process by which HIV and similar viruses leave the cell (other than by lysing).

Macronutrients

1) Elements needed by plants in relatively large (primary) or smaller (secondary) quantities. 2) Foods needed by animals daily or on a fairly regular basis.

Ovaries

1) In animals, the female gonads, which produce eggs (ova) and female sex hormones. 2) In flowers, part of the female reproductive structure in the carpel; contain the ovules, where egg development occurs. The lower part of the carpel that contains the ovules within which the female gametophyte develops.

Capsule

1) Structure produced around certain bacteria; 2) Structure produced by the bryophyte sporophyte that contains spores produced by meiosis.

Disaccharides

1) Sugars made up of two monosaccharides held together by a covalent bond; e.g., sucrose and lactose. 2) Type of sugar (saccharide) composed of two sugar molecules bonded together with an ester (covalent) bond examples include sucrose, maltose, and lactose.

Evolution

1) The change in life over time by adaptation, variation, over-reproduction, and differential survival/reproduction, a process referred to by Charles Darwin and Alfred Wallace as natural selection. 2) Descent with modification.

Messenger RNA (mRNA)

"Blueprint" for protein synthesis that is transcribed from one strand of the DNA (gene) and which is translated at the ribosome into a polypeptide sequence.

Bicarbonate Ions

A weak base present in saliva that helps to neutralize acids in food.

Community

All species or populations living in the same area.

Protostomes

Animals in which the first opening that appears in the embryo becomes the mouth; e.g., mollusks, annelids, and arthropods.

Phospholipids

Asymmetrical lipid molecules with a hydrophilic head and a hydrophobic tail. Lipids with a phosphate group in place of one of the three fatty acid chains. Phospholipids are the building blocks of cellular membranes. Phospholipids have hydrophilic heads (glycerol and phosphate) and hydrophobic tails (the non-polar fatty acids).

Isotopes

Atoms with the same atomic number but different numbers of neutrons; indicated by adding the mass number to the element's name, e.g., carbon 12 or 12C.

Social Behavior

Behavior that takes place in a social context and results from the interaction between and among individuals.

Courtship Behavior

Behavioral sequences that precede mating.

Interstitial

Being situated within a particular organ or tissue.

Positive Feedback

Biochemical control where the accumulation of the product stimulates production of an enzyme responsible for that product's production.

Appendix

Blind sac at the end of the large intestine that usually ruptures during final exams; a vestigial organ in humans.

Axillary Buds

Buds borne in the axil (where the leaf meets the stem) of a stem.

Terminal Buds

Buds located at the end of a plant shoot.

Bud Sports

Buds that produce fruit that is different from the rest of the fruit on the tree; vegetatively propagated by grafting cuttings onto another plant.

Megakaryocytes

Cells found in the bone marrow that produce platelets.

Biochemistry

Chemical processes associated with living things.

Ganglia

Clusters of neurons that receive and process signals.

Competitive Exclusion

Competition between species that is so intense that one species completely eliminates the second species from the area.

Kidney Stones

Crystallized deposits of excess wastes such as uric acid, calcium, and magnesium that may form in the kidney.

Peptic Ulcer

Damage to the epithelial layer of the stomach lining; generally caused by bacterial infection.

Z Lines

Dense areas in myofibrils that mark the beginning of the sarcomeres. The actin filaments of the sarcomeres are anchored in the Z lines.

Micronutrients

Elements that are required by plants in very small quantities, but are toxic in large quantities: iron, manganese, molybdenum, copper, boron, zinc, and chloride.

Primary Macronutrients

Elements that plants require in relatively large quantities: nitrogen, phosphorus, and potassium.

Secondary Macronutrients

Elements that plants require in relatively small quantities: calcium, magnesium, and sulfur.

Human Genome Project

Federally funded project to determine the DNA base sequence of every gene in the human genome.

Deoxyribose

Five-carbon sugar found in nucleotides of DNA.

Fossil Fuels

Fuels that are formed in the Earth from plant or animal remains; e.g., coal, petroleum, and natural gas.

Chromatid

Generally refers to a strand of a replicated chromosome; consists of DNA and protein.

Heterozygous

Having two different alleles (one dominant, one recessive) of a gene pair.

Transformation

In Griffith's experiments with strains of pneumonia bacterium, the process by which hereditary information passed from dead cells of one strain into cells of another strain, causing them to take on the characteristic virulence of the first strain.

Sensor

In a closed system, the element that detects change and signals the effector to initiate a response.

Effector

In a closed system, the element that initiates an action in response to a signal from a sensor. In human systems, a muscle or gland often serves as an effector.

Cell Body

In a neuron, the part that contains the nucleus and most of the cytoplasm and the organelles.

Coelom

In animals, a body cavity between the body wall and the digestive system that forms during pre adult development.

Asymmetrical

In animals, a term referring to organisms that lack a general body plan or axis of symmetry that divides the body into mirror-image halves.

Radially Symmetrical

In animals, refers to organisms with their body parts arranged around a central axis. Such animals tend to be circular or cylindrical in shape.

Bilateral Symmetry

In animals, refers to those that have a single axis of symmetry.

Notochord

In chordates, a cellular rod that runs the length of the body and provides dorsal support. Also, a structure of mesoderm in the embryo that will become the vertebrae of the spinal column. The stiff rod-like structure that all members of the Phylum Chordata develop at some stage during their life.

Macronucleus

In ciliates, the large nucleus that carries up to several hundred copies of the genome and controls metabolism and asexual reproduction.

Intron

In eukaryotes, bases of a gene transcribed but later excised from the mRNA prior to exporting from the nucleus and subsequent translation of the message into a polypeptide.

Cell Plate

In plants, a membrane-bound space produced during cytokinesis by the vesicles of the Golgi apparatus. The cell plate fuses with the plasma membrane, dividing the cell into two compartments.

Casparian Strip

In plants, an impermeable waxy layer between the cells of the endodermis that stops water and solutes from entering the xylem, except by passing through the cytoplasm of adjacent cells.

Nuclear Area

In prokaryotic cells, a region containing the cell's genetic information. Unlike the nucleus in eukaryotic cells, it is not surrounded by a membrane.

DNA Ligase

In recombinant DNA technology, an enzyme that seals together two DNA fragments from different sources to form a recombinant DNA molecule.

Expression

In relation to genes, the phenotypic manifestation of a trait. Expression may be age-dependent (e.g., Huntington disease) or affected by environmental factors (e.g., dark fur on Siamese cats).

Contrast

In relation to microscopes, the ability to distinguish different densities of structures.

Resolution

In relation to microscopes, the ability to view adjacent objects as distinct structures.

Micronucleus

In the protist group known as the ciliates, the small nucleus contains a single copy of the genome that is used for sexual reproduction.

Platelets

In vertebrates, cell fragments that bud off from the megakaryocytes in the bone marrow; carry chemicals needed for blood clotting. Cell fragment functioning in blood clotting.

Cones

Light receptors in primates' eyes that operate in bright light; provide color vision and visual acuity.

Emphysema

Lung disease characterized by shortness of breath, often associated with smoking.

Spindle Apparatus

Microtubule construction that aligns and segregates chromosomes during eukaryotic cell division.

Antigens

Molecules carried or produced by microorganisms that initiate antibody production; mostly proteins or proteins combined with polysaccharides.

Opsins

Molecules in cone cells that bind to pigments, creating a complex that is sensitive to light of a given wavelength.

Decay Series

Most radioisotopes do not decay into a stable daughter element in one single decay, but rather through a series of radioactive intermediaries.

Migration

Movement of organisms either permanently (as in the migration of humans to the Americas) or temporarily (migratory birds such as Canadian geese).

Brown Algae

Multicellular protists placed in the Division Phaeophyta, includes kelp.

Skeletal Muscle

Muscle that is generally attached to the skeleton and causes body parts to move; consists of muscle fibers. Voluntary muscle cells that have a striated appearance. These muscles control skeletal movements and are normally under conscious control.

Smooth Muscle

Muscle that lacks striations; found around circulatory system vessels and in the walls of such organs as the stomach, intestines, and bladder. Involuntary, not striated cells that control autonomic functions such as digestion and artery contraction.

Rodinia

Name applied to the precambrian supercontinent.

nares

Nostrils; the openings in the nose through which air enters.

Tubal Pregnancy

Occurs when the morula remains in the oviduct and does not descend into the uterus.

Malleus

One of the bones comprising the middle ear of mammals.

X-Chromosome

One of the sex chromosomes.

Centriole

Paired cellular organelle which functions in the organization of the mitotic spindle during cell division in eukaryotes.

Ordovician Extinction

Paleozoic-aged mass extinction possibly related to glaciation in the southern-hemisphere supercontinent Gondwana.

Somatostatin

Pancreatic hormone that controls the rate of nutrient absorption into the bloodstream.

Phylogenetic

Pertaining to a phylogeny.

Anaphase

Phase of mitosis in which the chromosomes begin to separate.

Red Tides

Phenomenon associated with population explosions (blooms) of certain types of dinoflagellates; red structures inside the dinoflagellates cause the water to have a reddish color.

Sieve Tube Members

Phloem cells that form long sieve tubes. See sieve elements.

Secondary Phloem

Phloem produced by the vascular cambium in a woody plant stem or root.

Sclereids

Plant cells with thick secondary walls that provide the gritty textures in pears.

Secondary (Lateral) Meristems

Plant meristems that produce secondary growth from a cambium.

Dermal System

Plant organ system that provides the covering for the plant.

Annuals

Plants that grow and reproduce sexually during one year.

Archaea

Proposed, but not widely accepted, sixth taxonomic kingdom that would include the archaebacteria.

RuBP

Ribulose bisphosphate; the 5-carbon chemical that combines with carbon dioxide at the beginning of the Calvin Cycle.

Lateral Roots

Roots extending away from the main (or taproot) root.

Thoroughfare Channels

Shortcuts within the capillary network that allow blood to bypass a capillary bed.

Silica

Silicon dioxide.

Integument

Something that covers or encloses, e.g., the skin.

Vascular Parenchyma

Specialized parenchyma cells in the phloem of plants.

Thorns

Stems modified to protect the plant.

Ascus

Structure produced by sac fungi in which sexual ascospores develop.

Epoch

Subdivision of a geological period.

Ribose

Sugar found in nucleotides of RNA and in ATP.

Scientific Method

Systematic approach of observation, hypothesis formation, hypothesis testing and hypothesis evaluation that forms the basis for modern science.

Suppressor T Cells

T cells that slow down and stop the immune response of B cells and other T cells. Immune system cells that shut off the antibody production when an infection is under control.

Embryo

Term applied to the zygote after the beginning of mitosis that produces a multicellular structure.

Deciduous

Term applied to trees that lose the leaves and have a dormancy period at least once per year.

Isotonic

Term applied to two solutions with equal solute concentrations.

Flora

Term collectively applied to all of the plants in an area. The botanical counterpart of fauna.

Adhesion

The ability of molecules of one substance to adhere to a different substance.

Haversian Canal

The central opening of compact bone; contains nerves and blood vessels.

Ventricle

The chamber of the heart that pumps the blood into the blood vessels that carry it away from the heart. The lower chamber of the heart through which blood leaves the heart.

Auricle

The chamber of the heart that receives blood from the body returned to the heart by the veins. Also referred to as atrium.

Stop Codon

The codon on a messenger RNA molecule where protein synthesis stops.

Clavicle

The collar bone.

Brush Border

The collection of microvilli forming a border on the intestinal side of the epithelial cells of the small intestine.

Extinction

The elimination of all individuals in a group, both by natural (dinosaurs, trilobites) and human-induced (dodo, passenger pigeon) means.

Micropyle

The end of the embryo sac where the egg cell and synergids are located.

Nephridium

The excretory organ in flatworms and other invertebrates; a blind-ended tube that expels waste through an excretory pore.

Gastric Pits

The folds and grooves into which the stomach lining is arranged.

Cohesion

The force that holds molecules of the same substance together.

Sarcomeres

The functional units of skeletal muscle; consist of filaments of myosin and actin.

Pelvis

The hollow cavity formed by the two hip bones.

Eon

The longest unit of geologic time.

Cervix

The lower neck of the uterus that opens into the vagina.

Tropism

The movement of plant parts toward or away from a stimulus in the plant's environment. Plant movement in response to an environmental stimulus.

Heart

The multicellular, chambered, muscular structure that pumps blood through the circulatory system by alternately contracting and relaxing.

Cork

The outer layer of the bark in woody plants; composed of dead cells.

Forebrain

The part of the brain that consists of the diencephalon and cerebrum.

Plantae

The plant kingdom; nonmobile, autotrophic, multicellular eukaryotes. Kingdom of the plants, autotrophic eukaryotes with cellulose in their cell walls and starch as a carbohydrate storage product, with chlorophylls a and b as photosynthesis pigments.

Osmoregulation

The regulation of the movement of water by osmosis into and out of cells; the maintenance of water balance within the body.

Luteal Phase

The second half of the ovarian cycle when the corpus luteum is formed; occurs after ovulation.

Population Dynamics

The study of the factors that affect the growth, stability, and decline of populations, as well as the interactions of those factors.

Genetics

The study of the structure and function of genes and the transmission of genes from parents to offspring.

Ileum

The third and last section of the small intestine.

Subatomic Particles

The three kinds of particles that make up atoms: protons, neutrons, and electrons.

Femur

The upper leg bone.

Myosin

Thick protein filaments in the center sections of sarcomeres.

Labia Minora

Thin membranous folds of skin outside the vaginal opening.

Triplet

Three-base sequence of mRNA that codes for a specific amino acid or termination codon.

Atrioventricular (AV) Node

Tissue in the right ventricle of the heart that receives the impulse from the atria and transmits it through the ventricles by way of the bundles of His and the Purkinje fibers.

Oils

Triglycerides that are liquid at room temperature.

Fats

Triglycerides that are solid at room temperature.

Bronchi

Tubes that carry air from the trachea to the lungs (sing.: bronchus).

Seminiferous Tubules

Tubules on the interior of the testes where sperm are produced.

Radiometric Time

Type of absolute time determined by the relative proportions of radioisotopes to stable daughter isotopes.

Molecules

Units of two or more atoms held together by chemical bonds. The combination of atoms by chemical bonds with the component atoms in definite proportions, such as water (two H to one O).

Petals

Usually brightly colored elements of a flower that may produce fragrant oils; non reproductive structures that attract pollinators. Sterile leaf-like (white, colorless, but usually colored) structures in flowers that serve to attract pollinators.

Aneuploidy

Variation in chromosome number involving one or a small number of chromosomes; commonly involves the gain or loss of a single chromosome.

Synaptic Vesicles

Vesicles at the synapse end of an axon that contain the neurotransmitters.

Bacteriophages

Viruses that attack and kill bacterial cells; composed only of DNA and protein.

Special Senses

Vision, hearing, taste, and smell.

Hydrophobic

Water-fearing.Term applied to nonpolar molecules that cannot bond with water.

Hydrophilic

Water-loving. Term applied to polar molecules that can form a hydrogen bond with water.

Suberin

Waxy, waterproof chemical in some plant cells, notably cork (in stems) and endodermis cells (in roots).

Soil

Weathered rocks and minerals combined with air, water and organic matter that can support plants.

Lymphocytes

White blood cells that arise in the bone marrow and mediate the immune response; include T cells and B cells.

Phagocytes

White blood cells that can engulf (by phagocytosis) and destroy microorganisms including viruses and bacteria; cells in this category include neutrophils and monocytes.

Monocytes

White blood cells that clean up dead viruses, bacteria, and fungi and dispose of dead cells and debris at the end of the inflammatory response.

Leaf Primordia

Young leaves, recently formed by the shoot apical meristem, located at the tip of a shoot.

Planktonic Organisms

"Floaters"; one of the two main types of organisms in the pelagic zone of the marine biome.

Nektonic Organisms

"Swimmers"; one of the two main types of organisms in the pelagic zone of the marine biome.

Electron Transport

1) A series of coupled oxidation/reduction reactions where electrons are passed like hot potatoes from one membrane-bound protein/enzyme to another before being finally attached to a terminal electron acceptor (usually oxygen or NADPH). ATP is formed by this process. 2) coupled series of oxidation/reduction reactions during which ATP is generated by energy transfer as electrons move from high reducing state to lower reducing state.

Families

1) In taxonomy, terms applied to subcategories within orders. 2) Term applied to a group of similar things, such as languages, chromosomes, etc.

Prophase

1) The first stage of mitosis during which chromosomes condense, the nuclear envelope disappears, and the centrioles divide and migrate to opposite ends of the cell. 2) The first stage of mitosis and meiosis (although in meiosis this phase is denoted with either a roman numeral I or II) where the chromatin condenses to form chromosomes, nucleolus dissolves, nuclear envelope dissolves, and the spindle begins to form.

Translocation

1) The movement of a segment from one chromosome to another without altering the number of chromosomes. 2) the movement of fluids through the phloem from one part of a plant to another, with the direction of movement depending on the pressure gradients between source and sink regions.

Fossil Record

1) The observed remains of once-living organisms taken as a whole.

Cortex

1) The outer part of an organ, e.g., the adrenal cortex, which produces several steroid hormones; 2) in plants, the region of the stem or root between the epidermis and the vascular bundle(s).

Epidermis

1) The outermost layer of skin that consists of several layers of epithelial cells and notably, keratinocytes and, in the inner layer of the epidermis, basal cells and melanocytes. 2) The outer layer of cells in the plant body, often covered by a waxy cuticle.

Fossil

1) The remains or traces of prehistoric life preserved in rocks of the Earth's crust. 2) Any evidence of past life.

Genome

1) The set of genes carried by an individual. 2) The set of genes shared by members of a reproductive unit such as a population or species.

Respiration

1) breathing as part of gas exchange; or 2) cellular metabolism.

Phylogeny

1) the study of evolutionary relationships within a monophyletic group. 2) evolutionary hypotheses represented as a dendrogram or branching diagram.

Colonial

10 Level of organization intermediate between unicellular and multicellular - organisms are composed of multiple cells but fail to exhibit specialization of those cells. Examples: Volvox, a colonial alga. 20 Term applied to organisms that occur in a fixed location, with one generation growing atop previous generations, as in coral reefs.

Loop of Henle

A U-shaped loop between the proximal and distal tubules in the kidney.

Blastula

A ball of cells surrounding a fluid-filled cavity (the blastocoel) that is produced by the repeated cleavage of a zygote.

Negative Feedback Loop

A biochemical pathway where the products of the reaction inhibit production of the enzyme that controlled their formation.

Sink

A body or process that acts as a storage device or disposal mechanism; e.g., plants and the oceans act as sinks absorbing atmospheric carbon dioxide. Also, a location in a plant where sugar is being consumed, either in metabolism or by conversion to starch.

Capillary Bed

A branching network of capillaries supplied by arterioles and drained by venules.

Target Cell

A cell that a particular hormone affects by its direct action (either passing through the membrane or binding to a surface receptor).

Somatic Cell

A cell that is not or will not become a gamete; the cells of the body.

Oocyte

A cell that will/is undergo/ing development into a female gamete.

Vascular Cylinder

A central column formed by the vascular tissue of a plant root; surrounded by parenchyma ground tissue.

Double Fertilization

A characteristic of angiosperms in which a pollen tube carries two sperm cells to the female gametophyte in the ovule. One sperm cell fuses with the egg cell and gives rise to a diploid embryo The other sperm cell fuses with the two polar cells to form a triploid cell that develops into the endosperm.

Covalent Bond

A chemical bond created by the sharing of electrons between atoms.

Ionic Bond

A chemical bond in which atoms of opposite charge are held together by electrostatic attraction.

Complement System

A chemical defense system that kills microorganisms directly, supplements the inflammatory response, and works with, or complements, the immune system.

Phosphate Group

A chemical group composed of a central phosphorus bonded to three or four oxygens. The net charge on the group is negative.

L-Dopa

A chemical related to dopamine that is used in the treatment of Parkinson's disease.

Acetylcholine

A chemical released at neuromuscular junctions that binds to receptors on the surface of the plasma membrane of muscle cells, causing an electrical impulse to be transmitted. The impulse ultimately leads to muscle contraction.

Histamine

A chemical released during the inflammatory response that increases capillary blood flow in the affected area, causing heat and redness.

Desmosome

A circular region of membrane cemented to an adjacent membrane by a molecular glue made of polysaccharides; found in tissues that undergo stretching.

Prostaglandins

A class of fatty acids that has many of the properties of hormones; synthesized and secreted by many body tissues and have a variety of effects on nearby cells.

Small Intestine

A coiled tube in the abdominal cavity that is the major site of chemical digestion and absorption of nutrients; composed of the duodenum, jejunum, and ileum.

Acquired Immunodeficiency Syndrome (AIDS)

A collection of disorders that develop as a result of infection by the human immunodeficiency virus (HIV), which attacks helper T cells, crippling the immune system and greatly reducing the body's ability to fight infection; results in premature death brought about by various diseases that overwhelm the compromised immune system.

Vulva

A collective term for the external genitals in women.

Adenosine Triphosphate (ATP)

A common form in which energy is stored in living systems; consists of a nucleotide (with ribose sugar) with three phosphate groups. The energy coin of the cell.

Closed Community

A community in which populations have similar range boundaries and density peaks; forms a discrete unit with sharp boundaries.

Open Community

A community in which the populations have different density peaks and range boundaries and are distributed more or less randomly.

Stressed Community

A community that is disturbed by human activity, such as road building or pollution, and is inadvertently simplified. Some species become superabundant while others disappear.

Food Web

A complex network of feeding interrelations among species in a natural ecosystem; more accurate and more complex depiction of energy flow than a food chain.

Chromatin

A complex of DNA and protein in eukaryotic cells that is dispersed throughout the nucleus during interphase and condensed into chromosomes during meiosis and mitosis.

Trisomy

A condition where a cell has an extra chromosome.

Cleavage Furrow

A constriction of the cell membrane at the equator of the cell that marks the beginning of cytokinesis in animal cells. The cell divides as the furrow deepens.

Vasectomy

A contraceptive procedure in men in which the vas deferens is cut and the cut ends are sealed to prevent the transportation of sperm. Surgical separation of the vas deferens so that sperm, while still produced, do not leave the body.

Tubal Ligation

A contraceptive procedure in women in which the oviducts are cut, preventing the ova from reaching the uterus.

Polar Covalent Bond

A covalent bond in which atoms share electrons in an unequal fashion. The resulting molecule has regions with positive and negative charges. The presence of polar covalent bonds allows other polar molecules to surround the molecule.

Peptide Bond

A covalent bond that links two amino acids together to form a polypeptide chain. A covalent bond between the amine end of one amino acid and the acid end of another amino acid.

Rheumatoid Arthritis

A crippling form of arthritis that begins with inflammation and thickening of the synovial membrane, followed by bone degeneration and disfigurement.

Spinal Cord

A cylinder of nerve tissue extending from the brain stem; receives sensory information and sends output motor signals; with the brain, forms the central nervous system. Nerve cell collections extending from the base of the brain to just below the last rib vertebrae.

Osteoarthritis

A degenerative condition associated with the wearing away of the protective cap of cartilage at the ends of bones. Bone growths or spurs develop, restricting movement and causing pain.

Evolutionary Tree

A diagram showing the evolutionary history of organisms based on differences in amino acid sequences. Organisms with fewer differences are placed closer together while those with more differences are further apart.

Diabetes Mellitus, Types I and II

A disorder associated with defects in insulin action. Type I diabetes is characterized by inadequate insulin secretion; Type II diabetes is characterized by impaired insulin secretion in response to elevated blood glucose levels or by loss of sensitivity to insulin by target cells.

Apnea

A disorder in which breathing stops for periods longer than 10 seconds during sleep; can be caused by failure of the automatic respiratory center to respond to elevated blood levels of carbon dioxide.

Osteoporosis

A disorder in which the mineral portion of bone is lost, making the bone weak and brittle; occurs most commonly in postmenopausal women.

Habitat Disruption

A disturbance of the physical environment in which a population lives.

Vitamins

A diverse group of organic molecules that are required for metabolic reactions and generally cannot be synthesized in the body.

Diaphragm

A dome-shaped muscle that separates the thoracic and abdominal cavities.

Camptodactyly

A dominant trait in which a muscle is improperly attached to bones in the little finger, causing the finger to be permanently bent.

Nerve Cord

A dorsal tubular cord of nervous tissue above the notochord of a chordate.

Saturated Fat

A fat with single covalent bonds between the carbons of its fatty acids.

Estrogen

A female sex hormone that performs many important functions in reproduction.

Zygote

A fertilized egg. A diploid cell resulting from fertilization of an egg by a sperm cell.

Periosteum

A fibrous membrane that covers bones and serves as the site of attachment for skeletal muscles; contains nerves, blood vessels, and lymphatic vessels.

Keratin

A fibrous protein that dills mature keratinocytes near the skin's surface.

Cuticle

A film composed of wax and cutin that occurs on the external surface of plant stems and leaves and helps to prevent water loss.

Epiglottis

A flap of tissue that seals off the windpipe and prevents food from entering. airway obstruction.

Phytoplankton

A floating layer of photosynthetic organisms, including algae, that are an important source of atmospheric oxygen and form the base of the aquatic food chain.

Intracellular Digestion

A form of digestion in which food is taken into cells by phagocytosis; found in sponges and most protozoa and coelenterates.

Phagocytosis

A form of endocytosis in which white blood cells surround and engulf invading bacteria or viruses.

Mutualism

A form of symbiosis in which both species benefit. A type of symbiosis where both organisms benefit. The classic example is lichens, which is a symbiosis between an alga and a fungus. The alga provides food and the fungus provides water and nutrients.

Parasitism

A form of symbiosis in which the population of one species benefits at the expense of the population of another species; similar to predation, but differs in that parasites act more slowly than predators and do not always kill the host. A type of symbiosis in which one organism benefits at the expense of the other, for example the influenza virus is a parasite on its human host. Viruses are obligate intracellular parasites.

Thermoacidophiles

A group of archaebacteria that are able to tolerate high temperatures and acidic pH.

Methanogens

A group of archaebacteria that produce methane as a by-product of their metabolism.

Trilobites

A group of benthic, detritus-feeding, extinct marine invertebrate animals (phylum Arthropoda), having skeletons of an organic compound called chitin. Trilobites appeared in abundance early in the Cambrian period and were dominant animals in the Burgess Shale fauna, before finally becoming extinct at the end of the Permian period.

Cycadeoids

A group of gymnosperm seed plants not closely related to, but superficially similar to, the cycads. Cycads and cycadeoids were dominant floristic elements of early and middle Mesozoic landscapes.This group is also known as the Bennettitaleans.

Auxins

A group of hormones involved in controlling plant growth and other functions; once thought responsible for phototropism by causing the cells on the shaded side of a plant to elongate, thereby causing the plant to bend toward the light.

Cytokinins

A group of hormones that promote cell division and inhibit aging of green tissues in plants.

Gibberellins

A group of hormones that stimulate cell division and elongation in plants. Gibberellic acid (GA), the first of this class to be discovered, causes bolting (extreme elongation) of stems. GA is also applied to certain plants to promote larger fruits.

Population

A group of individuals of the same species living in the same area at the same time and sharing a common gene pool. A group of potentially interbreeding organisms in a geographic area.

Monophyletic Group

A group of organisms descended from a common ancestor. For example: your immediate family may be considered such a group, being descended from a common ancestral group (grandparents, etc.).

Mineralocorticoids

A group of steroid hormones produced by the adrenal cortex that are important in maintaining electrolyte balance.

Glucocorticoids

A group of steroid hormones produced by the adrenal cortex that are important in regulating the metabolism of carbohydrates, fats, and proteins.

Epinephrine

A hormone produced by the adrenal medulla and secreted under stress; contributes to the "fight or flight" response.

Adrenocorticotropic Hormone (ACTH)

A hormone produced by the anterior pituitary that stimulates the adrenal cortex to release several hormones including cortisol.

Thyroid-Stimulating Hormone

A hormone produced by the anterior pituitary that stimulates the production and release of thyroid hormones.

Prolactin

A hormone produced by the anterior pituitary; secreted at the end of pregnancy when it activates milk production by the mammary glands.

Antidiuretic Hormone (ADH)

A hormone produced by the hypothalamus and released by the pituitary gland that increases the permeability of the renal tubule of the nephron and thereby increases water reabsorption; also known as vasopressin.

Gonadotropin-Releasing Hormone (GnRH)

A hormone produced by the hypothalamus that controls the secretion of luteinizing hormone.

Gastrin

A hormone produced by the pyloric gland area of the stomach that stimulates the secretion of gastric acids.

calcitonin

A hormone produced by the thyroid that plays a role in regulating calcium levels.

Norepinephrine

A hormone produced in the adrenal medulla and secreted under stress; contributes to the "fight or flight" response.

Secretin

A hormone produced in the duodenum that stimulates alkaline secretions by the pancreas and inhibits gastric emptying.

Glucagon

A hormone released by the pancreas that stimulates the breakdown of glycogen and the release of glucose, thereby increasing blood levels of glucose. Glucagon and insulin work together to maintain blood sugar levels.

Aldosterone

A hormone secreted by the adrenal glands that controls the reabsorption of sodium in the renal tubule of the nephron.

Luteinizing Hormone (LH)

A hormone secreted by the anterior pituitary gland that stimulates the secretion of testosterone in men and estrogen in women.

Follicle-Stimulating Hormone (FSH)

A hormone secreted by the anterior pituitary that promotes gamete formation in both males and females.

Insulin

A hormone secreted by the pancreas that stimulates the uptake of glucose by body cells. Insulin works antagonistically with glucagon to control blood sugar levels.

Cholecystokinin

A hormone secreted in the duodenum that causes the gallbladder to release bile and the pancreas to secrete lipase.

Hemophilia

A human sex-linked recessive genetic disorder that results in the absence of certain blood-clotting factors, usually Factor VII. Hemophiliacs suffer from an inability to clot their blood.

Zebroid

A hybrid animal that results from breeding zebras and horses.

Theory

A hypothesis that has withstood extensive testing by a variety of methods, and in which a higher degree of certainty may be placed. A theory is NEVER a fact, but instead is an attempt to explain one or more facts.

Gaia

A hypothetical superorganism composed of the Earth's four spheres: the biosphere, hydrosphere, lithosphere, and atmosphere.

Immovable Joint

A joint in which the bones interlock and are held together by fibers or bony processes that prevent the joint from moving; e.g., the bones of the cranium.

Membrane-Attack Complex (MAC)

A large cylindrical multiprotein complex formed by the complement system; kills invading microorganisms by embedding in their plasma membrane, creating a pore through which fluid flows, ultimately causing the cell to burst.

Crustaceans

A large taxonomic class of arthropods that includes lobsters, shrimps, and crabs.

Biome

A large-scale grouping that includes many communities of a similar nature.

Cambium

A lateral meristem in plants. Types of cambiums include vascular, cork, and intercalary.

Middle Lamella

A layer composed of pectin that cements two adjoining plant cells together.

Endodermis

A layer of cells surrounding the vascular cylinder of plants.

Perichondrium

A layer of connective tissue that forms around the cartilage during bone formation. Cells in the perichondrium lay down a peripheral layer that develops into compact bone.

Cork Cambium

A layer of lateral meristematic tissue between the cork and the phloem in the bark of woody plants.

Vascular Cambium

A layer of lateral meristematic tissue between the xylem and phloem in the stems of woody plants. Lateral meristem tissue in plants that produces secondary growth.

Simple Leaf

A leaf in which the blade does not form leaflets.

Compound Leaf

A leaf in which the blade forms small leaflets. Compound leaves that have several small leaflets originating from a central axis are termed pinnately compound; example: rose. Compound leaves that have their leaflets originating from a common point are termed palmately compound; example: palm.

Stalk

A leaf's petiole; the slender stem that supports the blade of a leaf and attaches it to a larger stem of the plant.

Cotyledon

A leaf-like structure that is present in the seeds of flowering plants; appears during seed germination and sometimes is referred to as a seed leaf.

Alternation of Generations

A life cycle in which a multicellular diploid stage is followed by a haploid stage and so on; found in land plants and many algae and fungi.

Smog

A local alteration in the atmosphere caused by human activity; mainly an urban problem that is often due to pollutants produced by fuel combustion.

Epididymis

A long, convoluted duct on the testes where sperm are stored.

Bolus

A mass of chewed food mixed with salivary secretions that is propelled into the esophagus during the swallowing phase of digestion.

Fitness

A measure of an individual's ability to survive and reproduce; the chance that an individual will leave more offspring in the next generation than other individuals.

Apical Meristem

A meristem (embryonic tissue) at the tip of a shoot or root that is responsible for increasing the plant's length.

Polymerase Chain Reaction (PCR)

A method of amplifying or copying DNA fragments that is faster than cloning. The fragments are combined with DNA polymerase, nucleotides, and other components to form a mixture in which the DNA is cyclically amplified.

Amniocentesis

A method of prenatal testing in which amniotic fluid is withdrawn from the uterus through a needle. The fluid and the fetal cells it contains are analyzed to detect biochemical or chromosomal disorders.

Chorionic Villi Sampling (CVS)

A method of prenatal testing in which fetal cells from the fetal side of the placenta (chorionic villi) are extracted and analyzed for chromosomal and biochemical defects.

Asexual Reproduction

A method of reproduction in which genetically identical offspring are produced from a single parent; occurs by many mechanisms, including fission, budding, and fragmentation.

Semen

A mixture of sperm and various glandular secretions.

Big Bang Theory

A model for the evolution of the universe that holds that all matter and energy in the universe were concentrated in one point, which suddenly exploded. Subsequently, matter condensed to form atoms, elements, and eventually galaxies and stars.

Logistic Growth Model

A model of population growth in which the population initially grows at an exponential rate until it is limited by some factor; then, the population enters a slower growth phase and eventually stabilizes.

Punctuated Equilibrium

A model that holds that the evolutionary process is characterized by long periods with little or no change interspersed with short periods of rapid speciation.

Electron Acceptor

A molecule that forms part of the electron transport system that transfers electrons ejected by chlorophyll during photosynthesis. Part of the energy carried by the electrons is transferred to ATP, part is transferred to NADPH, and part is lost in the transfer system.

Arrector Pili

A muscle running from a hair follicle to the dermis. Contraction of the muscle causes the hair to rise perpendicular to the skin surface, forming "goose pimples."

Ureter

A muscular tube that transports urine by peristaltic contractions from the kidney to the bladder.

Urethra

A narrow tube that transports urine from the bladder to the outside of the body. In males, it also conducts sperm and semen to the outside.

Nyctinasty

A nastic movement in a plant that is caused by light and dark.

Mitotic Spindle

A network of microtubules formed during prophase. Some microtubules attach to the centromeres of the chromosomes and help draw the chromosomes apart during anaphase.

Midbrain

A network of neurons that connects with the forebrain and relays sensory signals to other integrating centers.

Deoxyribonucleic Acid (DNA)

A nucleic acid composed of two polynucleotide strands wound around a central axis to form a double helix; the repository of genetic information. Nucleic acid that functions as the physical carrier of inheritance for 99% of all species. The molecule is double-stranded and composed of two strands in an antiparallel and complementary arrangement. The basic unit, the nucleotide, consists of a molecule of deoxyribose sugar, a phosphate group, and one of four nitrogenous bases.

Homologues

A pair of chromosomes in which one member of the pair is obtained from the organism's maternal parent and the other from the paternal parent; found in diploid cells. Also commonly referred to as homologous chromosomes.

Antagonistic Muscles

A pair of muscles that work to produce opposite effects; one contracts as the other relaxes: for example, the bicep and tricep muscles on opposite sides of your upper arm.

Mosaic Evolution

A pattern of evolution where all features of an organism do not evolve at the same rate. Some characteristics are retained from the ancestral condition while others are more recently evolved.

Growth Hormone (GH)

A peptide hormone produced by the anterior pituitary that is essential for growth.

Human Chorionic Gonadotropin (hCG)

A peptide hormone secreted by the chorion that prolongs the life of the corpus luteum and prevents the breakdown of the uterine lining.

Oxytocin

A peptide hormone secreted by the posterior pituitary that stimulates the contraction of the uterus during childbirth.

Brachiopods

A phylum of hinge-shelled animals that have left an excellent fossil record; brachiopods live on or in the ocean floor.

Stimulus

A physical or chemical change in the environment that leads to a response controlled by the nervous system.

Phytochrome

A pigment in plant leaves that detects day length and generates a response; partly responsible for photoperiodism.

Melanin

A pigment that gives the skin color and protects the underlying layers against damage by ultraviolet light; produced by melanocytes in the inner layer of the epidermis.

"One Gene, One Polypeptide" Hypothesis

A revision of the one gene, one enzyme hypothesis. Some proteins are composed of different polypeptide chains encoded by separate genes, so the hypothesis now holds that mutation in a gene encoding a specific polypeptide can alter the ability of the encoded protein to function and thus produce an altered phenotype.

Stromatolite

A sedimentological and biological "fossil" representing colonies of bacteria alternating with layers of sediments. Becoming more common during the Proterozoic, stromatolites persist today in marine environments where grazing by herbivorous organisms is limited.

Anticodon

A sequence of three nucleotides on the transfer RNA molecule that recognizes and pairs with a specific codon on a messenger RNA molecule; helps control the sequence of amino acids in a growing polypeptide chain.

Palindrome

A sequence that reads the same in either direction; in genetics, refers to an enzyme recognition sequence that reads the same on both strands of DNA.

Restriction Enzymes

A series of enzymes that attach to DNA molecules at specific nucleotide sequences and cut both strands of DNA at those sites. A bacterial enzyme that cuts DNA at a specific recognition sequence. This is a bacterial defense against viral DNA and plasmid DNA and is now used as an important tool in biotechnology.

Metabolic Pathway

A series of individual chemical reactions in a living system that combine to perform one or more important functions. The product of one reaction in a pathway serves as the substrate for the following reaction. Examples include glycolysis and Kreb's cycle.

Recombinant DNA Technology

A series of techniques in which DNA fragments are linked to self-replicating forms of DNA to create recombinant DNA molecules. These molecules in turn are replicated in a host cell to create clones of the inserted segments.

Anaphylaxis

A severe allergic reaction in which histamine is released into the circulatory system; occurs upon subsequent exposure to a particular antigen; also called anaphylactic shock.

Syphilis

A sexually transmitted disease caused by a bacterial infection that produces an ulcer on the genitals and can have potentially serious effects if untreated.

Chlamydia

A sexually transmitted disease caused by a parasitic bacterium that lives inside cells of the reproductive tract.

Genital Herpes

A sexually transmitted disease caused by the herpes virus; results in sores on the mucous membranes of the mouth or genitals.

Gonorrhea

A sexually transmitted disease that is caused by a bacterium that inflames and damages epithelial cells of the reproductive system.

Glucose

A six-carbon single sugar; the most common energy source.

Pituitary Gland

A small gland located at the base of the brain; consists of an anterior and a posterior lobe and produces numerous hormones. The master gland of the endocrine system, the pituitary releases hormones that have specific targets as well as those that stimulate other glands to secrete hormones. Part of the pituitary is nerve tissue, the rest is glandular epithelium.

Microevolution

A small-scale evolutionary event such as the formation of a species from a preexisting one or the divergence of reproductively isolated populations into new species.

Dominance Hierarchy

A social structure among a group of animals in which one is dominant and the others have subordinate nonbreeding positions.

Hypertonic

A solution having a high concentration of solute.

Hypotonic

A solution having a low concentration of solute.

Flame Cell

A specialized cell at the blind end of a nephridium that filters body fluids.

Centromere

A specialized region on each chromatid to which kinetochores and sister chromatids attach.

Larva

A stage in the development of many insects and other organisms including sea urchins and sponges. In sponges, sexual reproduction results in the production of motile ciliated larvae.

Basal Body

A structure at the base of a cilium or flagellum; consists of nine triplet microtubules arranged in a circle with no central microtubule.

Corpus Luteum

A structure formed from the ovulated follicle in the ovary; secretes progesterone and estrogen.

Proton

A subatomic particle in the nucleus of an atom that carries a positive charge. The positively charged (+1) subatomic particle is located in the atomic nucleus and has a mass slightly less than that of a neutron. Elements differ by the number of protons in their atoms.

Electron

A subatomic particle with a negative charge. Electrons circle the atom's nucleus in regions of space known as orbitals.

Element

A substance composed of atoms with the same atomic number; cannot be broken down in ordinary chemical reactions.

Base

A substance that lowers the hydrogen ion concentration in a solution.

Nicotine Adenine Dinucleotide Phosphate (NADP+)

A substance to which electrons are transferred from photosystem I during photosynthesis; the addition of the electrons reduces NADP, which acquires a hydrogen ion to form NADPH, which is a storage form of energy that can be transferred to the Calvin Cycle for the production of carbohydrate.

Commensalism

A symbiotic relationship in which one species benefits and the other is not affected.

Circulatory System, Open

A system in which the circulating fluid is not enclosed in vessels at all times; found in insects, crayfish, some mollusks, and other invertebrates.

Binomial System of Nomenclature

A system of taxonomy developed by Linnaeus in the early eighteenth century. Each species of plant and animal receives a two-term name; the first term is the genus, and the second is the species.

Circulatory System, Closed

A system that uses a continuous series of vessels of different sizes to deliver blood to body cells and return it to the heart; found in echinoderms and vertebrates.

Taxonomy

A systematic method of classifying plants and animals. Classification of organisms based on degrees of similarity purportedly representing evolutionary (phylogenetic) relatedness.

Subspecies

A taxonomic subdivision of a species; a population of a particular region genetically distinguishable from other such populations and capable of interbreeding with them.

Bony Fish

A term applied collectively to all groups of fish with bony (as opposed to cartilaginous) skeletons.

Fibroblast

A term applied to a cell of connective tissue that is separated from similar cells by some degree of matrix material; fibroblasts secrete elastin and collagen protein fibers.

Pleiotropic

A term describing a genotype with multiple phenotypic effects. For example: sickle-cell anemia produces a multitude of consequences in those it affects, such as heart disease, kidney problem, etc.

Mucus

A thick, lubricating fluid produced by the mucous membranes that line the respiratory, digestive, urinary, and reproductive tracts; serves as a barrier against infection and, in the digestive tract, moistens food, making it easier to swallow.

Pleura

A thin sheet of epithelium that covers the inside of the thoracic cavity and the outer surface of the lungs.

Respiratory Surface

A thin, moist, epithelial surface that oxygen can cross to move into the body and carbon dioxide can cross to move out of the body.

PGA (Phosphoglycerate)

A three-carbon molecule formed when carbon dioxide is added to ribulose biphosphate (RuBP) during the dark reaction of photosynthesis (Calvin, or Calvin-Benson Cycle). PGA is converted to PGAL, using ATP and NADPH.

Tube-Within-A-Tube System

A type of body plan in animals. The organism has two openings - one for food and one for the elimination of waste and a specialized digestive system.

Eukaryote

A type of cell found in many organisms including single-celled protists and multicellular fungi, plants, and animals; characterized by a membrane-bounded nucleus and other membranous organelles; an organism composed of such cells. The first eukaryotes are encountered in rocks approximately 1.2-1.5 billion years old.

Pedigree Analysis

A type of genetic analysis in which a trait is traced through several generations of a family to determine how the trait is inherited. The information is displayed in a pedigree chart using standard symbols.

Codominance

A type of inheritance in which heterozygotes fully express both alleles.

Incomplete Dominance

A type of inheritance in which the heterozygote has a phenotype intermediate to those of the homozygous parents.

Lungfish

A type of lobe-finned fish that breathe by a modified swim bladder (or lung) as well as by gills.

Crossopterygians

A type of lobe-finned fish with lungs that were ancestral to amphibians.

Helper T Cells

A type of lymphocyte that stimulates the production of antibodies by activating B cells when an antigen is present.

Insertion

A type of mutation in which a new DNA base is inserted into an existing sequence of DNA bases. This shifts the reference frame in protein synthesis, resulting (sometimes) in altered amino acid sequences.

Substitution

A type of mutation in which one base is substituted for another.

Trypanosomes

A type of roundworm, responsible for human disease associated with eating raw or undercooked pork.

Rhodopsin

A visual pigment contained in the rods of the retina in the eye.

Recombination

A way in which meiosis produces new combinations of genetic information. During synapsis, chromatids may exchange parts with other chromatids, leading to a physical exchange of chromosome parts; thus, genes from both parents may be combined on the same chromosome, creating a new combination.

Assortment

A way in which meiosis produces new combinations of genetic information. Paternal and maternal chromosomes line up randomly during synapsis, so each daughter cell is likely to receive an assortment of maternal and paternal chromosomes rather than a complete set from either.

Food Pyramid

A way of depicting energy flow in an ecosystem; shows producers (mostly plants or other phototrophs) on the first level and consumers on the higher levels.

Hydrogen Bond

A weak bond between two atoms (one of which is hydrogen) with partial but opposite electrical charges.

Polyploidy

Abnormal variation in the number of chromosome sets. The condition when a cell or organism has more than the customary two sets of chromosomes. This is an especially effective speciation mechanism in plants since the extra chromosomes will establish reproductive isolation with the parental population(s), an essential for speciation.

Biosphere

All ecosystems on Earth as well as the Earth's crust, waters, and atmosphere on and in which organisms exist; also, the sum of all living matter on Earth.

Somatic Senses

All senses except vision, hearing, taste, and smell; include pain, temperature, and pressure.

Amino Acid Sequence

Also known as the primary structure of a protein/polypeptide; the sequence of amino acids in a protein/polypeptide controlled by the sequence of DNA bases.

Alleles

Alternate forms of a gene.

Embryo Sac

Alternate term applied to the angiosperm female gametophyte contained within a megaspore.

Amoebocytes

Amoeboid cells in sponges that occur in the matrix between the epidermal and collar cells. They transport nutrients.

Chlorophyll B

An accessory chlorophyll found in green algae and plants.

Chlorophyll C

An accessory chlorophyll found in some protists.

Phycocyanin

An accessory pigment found in cyanobacteria and the chloroplasts of red algae.

Phycoerythrin

An accessory pigment found in cyanobacteria and the chloroplasts of red algae.

Countercurrent Flow

An arrangement by which fish obtain oxygen from the water that flows through their gills. Water flows across the respiratory surface of the gill in one direction while blood flows in the other direction through the blood vessels on the other side of the surface.

Portal System

An arrangement in which capillaries drain into a vein that opens into another capillary network.

Ion

An atom that has lost or gained electrons from its outer shell and therefore has a positive or negative charge, respectively; symbolized by a superscript plus or minus sign and sometimes a number, e.g., H+, Na+1, Cl-2.

Nucleus (Atom)

An atom's core; contains protons and one or more neutrons (except hydrogen, which has no neutrons).

Cystic Fibrosis

An autosomal recessive genetic disorder that causes the production of mucus that clogs the airways of the lungs and the ducts of the pancreas and other secretory glands.

Amniote Egg

An egg with compartmentalized sacs (a liquid-filled sac in which the embryo develops, a food sac, and a waste sac) that allows vertebrates to reproduce on land.

Pepsin

An enzyme produced from pepsinogen that initiates protein digestion by breaking down protein into large peptide fragments. An enzyme, produced by the stomach, that chemically breaks down peptide bonds in polypeptides and proteins.

Renin

An enzyme secreted by the kidneys that converts angiotensinogen into angiotensin II.

Salivary Amylase

An enzyme secreted by the salivary glands that begins the breakdown of complex sugars and starches.

Reverse Transcriptase

An enzyme used in the replication of retroviruses; aids in copying the retrovirus's RNA into a complementary strand of DNA once inside the host cell.

Clone

An exact copy of a DNA segment; produced by recombinant DNA technology.

Archaeocyathids

An extinct group of animals that were part of Cambrian-aged reef environments, but which were extinct by the close of the Cambrian Period.

Duplication

An extra copy of a chromosome segment without altering the number of chromosomes.

Exponential Rate

An extremely rapid increase, e.g., in the rate of population growth.

Hypothesis

An idea that can be experimentally tested; an idea with the lowest level of confidence.

Pepsinogen

An inactive form of pepsin; synthesized and stored in cells lining the gastric pits of the stomach.

Organism

An individual, composed of organ systems (if multicellular). Multiple organisms make up a population.

Thecodonts

An informal term for a variety of Permian and Triassic reptiles that had teeth set in individual sockets. Small, bipedal thecodontia are the probable ancestors of dinosaurs.

Symbiosis

An interactive association between two or more species living together; may be parasitic, commensal, or mutualistic. The relationship between two organisms.

Nerve Net

An interconnected mesh of neurons that sends signals in all directions; found in radially symmetrical marine invertebrates, such as jellyfish and sea anemones, that have no head region or brain.

Acetyl CoA

An intermediate compound formed during the breakdown of glucose by adding a two-carbon fragment to a carrier molecule (Coenzyme A or CoA).

Endoskeleton

An internal supporting skeleton with muscles on the outside; in vertebrates, consists of the skull, spinal column, ribs, and appendages.

Placenta

An organ produced from interlocking maternal and embryonic tissue in placental mammals; supplies nutrients to the embryo and fetus and removes wastes.

Spleen

An organ that produces lymphocytes and stores erythrocytes.

Monomer

An organic chemical unit linked to other units (usually by a covalent bond formed by the removal of water) to produce a larger molecule (macromolecule) known as a polymer.

Neutron

An uncharged subatomic particle in the nucleus of an atom. The large (mass approximately equal to 1 atomic mass unit), electrically neutral particle that may occur in the atomic nucleus.

Archaebacteria

Ancient (over 3.5 billion years old) group of prokaryotes; some biologists want to place this group into a separate Kingdom, the Archaea. Most currently place it within the Kingdom Monera.

Animalia

Animal Kingdom. Multicellular eukaryotic group characterized by heterotrophic nutritional mode, usually organ and tissue development, and motility sometime during the organism's life history.

Connective Tissue

Animal tissue composed of cells embedded in a matrix (gel, elastic fibers, liquid, or inorganic minerals). Includes loose, dense, and fibrous connective tissues that provide strength (bone, cartilage), storage (bone, adipose), and flexibility (tendons, ligaments).

Deuterostomes

Animals in which the first opening that appears in the embryo becomes the anus while the mouth appears at the other end of the digestive system. Main groups include chordates and echinoderms.

Fluid Feeders

Animals such as aphids, ticks, and mosquitoes that pierce the body of a host plant or animal and obtain food from ingesting its fluids.

Substrate Feeders

Animals such as earthworms or termites that eat the soil or wood through which they burrow.

Absorptive Feeders

Animals such as tapeworms that ingest food through the body wall.

Acoelomates

Animals that do not have a coelom or body cavity; e.g., sponges and flatworms.

Pseudocoelomates

Animals that have a body cavity that is in direct contact with the outer muscular layer of the body and does not arise by splitting of the mesoderm; e.g., roundworms.

Coelomates

Animals that have a coelom or body cavity lined with mesoderm.

Endotherms

Animals that have the ability to maintain a constant body temperature over a wide range of environmental conditions.

Ingestive Feeders

Animals that ingest food through a mouth.

Ectotherms

Animals with a variable body temperature that is determined by the environment. Examples: fish, frogs, and reptiles.

Allergens

Antigens that provoke an allergic reaction.

Vertebrate

Any animal having a segmented vertebral column; members of the subphylum Vertebrata; include reptiles, fishes, mammals, and birds.

Mutation

Any heritable change in the nucleotide sequence of DNA; can involve substitutions, insertions, or deletions of one or more nucleotides.

Trace Fossil

Any indication of prehistoric organic activity, such as tracks, trails, burrows, or nests.

Dinosaurs

Any of the Mesozoic diapsids (once considered to be reptiles) belonging to the groups designated as ornithischians and saurischians.

Sedimentary Rock

Any rock composed of sediment, i.e., solid particles and dissolved minerals. Examples include rocks that form from sand or mud in riverbeds or on the sea bottom.

Matter

Anything that has mass and occupies space.

Zone of Differentiation

Area in plant roots where recently produced cells develop into different cell types.

Zone of Elongation

Area in plant roots where recently produced cells grow and elongate prior to differentiation.

Binding Sites

Areas on the ribosome within which tRNA-amino acid complexes fit during protein synthesis.

Coronary Arteries

Arteries that supply the heart's muscle fibers with nutrients and oxygen.

Vernalization

Artificial exposure of seeds or seedlings to cold to enable the plant to flower.

Altitudinal Gradient

As altitude increases, a gradient of cooler, drier conditions occurs.

Latitudinal Gradient

As latitude increases, a gradient of cooler, drier conditions occurs.

Lichens

Autotrophic organisms composed of a fungus (sac or club fungus) and a photosynthetic unicellular organism (e.g., a cyanobacterium or alga) in a symbiotic relationship; are resistant to extremes of cold and drought and can grow in marginal areas such as Arctic tundra.

Mole

Avogadro's number (6.02 X 1023 atoms) of a substance.

Trichocysts

Barbed, thread-like organelles of ciliated protozoans that can be discharged for defense or to capture prey.

Kreb's Cycle

Biochemical cycle in cellular aerobic metabolism where acetyl CoA is combined with oxaloacetate to form citric acid; the resulting citric acid is converted into a number of other chemicals, eventually reforming oxaloacetate; NADH, some ATP, and FADH2 are produced and carbon dioxide is released.

Transition Reaction

Biochemical process of converting 3-carbon pyruvate into 2-carbon acetyl and attaching it to coenzyme A (CoA) so it can enter Krebs cycle. Carbon dioxide is also released and NADH is formed (from NAD and H) in this process.

Biodiversity

Biological diversity; can be measured in terms of genetic, species, or ecosystem diversity.

Reproductive Isolating Mechanism

Biological or behavioral characteristics that reduce or prevent interbreeding with other populations; e.g., the production of sterile hybrids. Establishment of reproductive isolation is considered essential for development of a new species.

Circadian Rhythms

Biorhythms that occur on a daily cycle.

Superior Vena Cava

Blood from the head returns to the heart through this main vein.

Cyanobacteria

Blue-green bacteria; unicellular or filamentous chains of cells that carry out photosynthesis.

Homologous Structures

Body parts in different organisms that have similar bones and similar arrangements of muscles, blood vessels, and nerves and undergo similar embryological development, but do not necessarily serve the same function; e.g., the flipper of a whale and the forelimb of a horse.

Analogous Structures

Body parts that serve the same function in different organisms, but differ in structure and embryological development; e. g., the wings of insects and birds.

Osteocytes

Bone cells that lay down new bone; found in the concentric layers of compact bone. Bone cell, a type of connective tissue.

Osteoblasts

Bone-forming cells.

Fucoxanthin

Brown accessory pigment found in and characteristic of the brown algae.

Tendons

Bundles of connective tissue that link muscle to bone. Fibrous connective tissue that connects muscle to bone.

Nerves

Bundles of neuronal processes enclosed in connective tissue that carry signals to and from the central nervous system.

Organelles

Cell components that carry out individual functions; e.g., the cell nucleus and the endoplasmic reticulum. Subcellular structures (usually membrane-bound and unique to eukaryotes) that perform some function, e.g. chloroplast, mitochondrion, nucleus.

Meiosis

Cell division in which the chromosomes replicate, followed by two nuclear divisions. Each of the resulting gametes (in animals, spores in plants) receives a haploid set of chromosomes. Reduction/division by which ploidy, the number of sets of homologous chromosomes, is reduced in the formation of haploid cells that become gametes (or gametophytes in plants).

Multinucleate

Cells having more than one nucleus per cell.

Secondary Growth

Cells in a plant that are produced by a cambium. Increase in girth of a plant due to the action of lateral meristems such as the vascular cambium. The main cell produced in secondary growth is secondary xylem, better known as wood.

Epithelial Tissue

Cells in animals that are closely packed in either single or multiple layers, and which cover both internal and external surfaces of the animal body. Also referred to as epithelium.

Stem Cells

Cells in bone marrow that produce lymphocytes by mitotic division.

Synergid

Cells in the embryo sac of angiosperms that flank the egg cell. The pollen tube grows through one (usually the smaller) of the synergids.

Microspore Mother Cell

Cells in the microsporangium that undergo meiosis to produce microspores. In flowering plants the microspore is known as the pollen grain, and contains a three-celled male.

Primary Growth

Cells produced by an apical meristem. The growth of a plant by the actions of apical meristems on the shoot and root apices in producing plant primary tissues.

Plasma Cells

Cells produced from B cells that synthesize and release antibodies.

Diploid

Cells that contain homologous chromosomes. The number of chromosomes in the cells is the diploid number and is equal to 2n (n is the number of homologous pairs).

Haploid

Cells that contain only one member of each homologous pair of chromosomes (haploid number = n). At fertilization, two haploid gametes fuse to form a single cell with a diploid number of chromosomes.

Osteoclasts

Cells that remove material to form the central cavity in a long bone.

Mast Cells

Cells that synthesize and release histamine, as during an allergic response; found most often in connective tissue surrounding blood vessels.

Megaspore Mother Cell

Cells that undergo meiosis to produce megaspores.

Pith

Central area in plant stems, largely composed of parenchyma tissue modified for storage.

Desert Biome

Characterized by dry conditions and plants and animals that have adapted to those conditions; found in areas where local or global influences block rainfall.

Carrageenan

Chemical extracted from red algae that is added to commercial ice creams as an emulsifying agent.

Endergonic

Chemical reactions that require energy input to begin.

Pheromones

Chemical signals that travel between organisms rather than between cells within an organism; serve as a form of communication between animals.

Hormones

Chemical substances that are produced in the endocrine glands and travel in the blood to target organs where they elicit a response.

Chlorofluorocarbons (CFCs)

Chemical substances used in refrigerators, air conditioners, and solvents that drift to the upper stratosphere and dissociate. Chlorine released by CFCs reacts with ozone, eroding the ozone layer.

Calcium Carbonate

Chemical that also occurs in limestone and marble.

Neurotoxin

Chemical that paralyzes nerves. Neurotoxins are produced by a variety of organisms, most notably some of the heterotrophic dinoflagellates.

Primary Compounds

Chemicals made by plants and needed for the plant's own metabolism.

Antinutrients

Chemicals produced by plants as a defense mechanism; inhibit the action of digestive enzymes in insects that attack and attempt to eat the plants.

Neurotransmitters

Chemicals released from the tip of an axon into the synaptic cleft when a nerve impulse arrives; may stimulate or inhibit the next neuron. The chemical that crosses the synaptic cleft and causes the transmission of the nerve message in an adjacent neuron or the stimulation of an effector cell (muscle or gland).

Coenzymes

Chemicals required by a number of enzymes for proper functioning; also known as enzyme cofactors.

Pesticides

Chemicals that are applied to agricultural crops or domesticated plants and which kill or inhibit growth of insects.

Buffers

Chemicals that maintain pH values within narrow limits by absorbing or releasing hydrogen ions.

Angina

Chest pain, especially during physical exertion or emotional stress, that is caused by gradual blockage of the coronary arteries.

Sister Chromatids

Chromatids joined by a common centromere and carrying identical genetic information (unless crossing-over has occurred).

Amphibians

Class of terrestrial vertebrates which lay their eggs (and also mate) in water but live on land as adults following a juvenile stage where they live in water and breathe through gills. Amphibians were the first group of land vertebrates; today they are mostly restricted to moist habitats.

Pancreatic Islets

Clusters of endocrine cells in the pancreas that secrete insulin and glucagon; also known as islets of Langerhans.

Photosystems

Clusters of several hundred molecules of chlorophyll in a thylakoid in which photosynthesis takes place. Eukaryotes have two types of photosystems: I and II. The series of green photoreceptive pigments involved in the light reactions, which occur in the thylakoids of the chloroplast (in eukaryotes). Energy from light is passed to the electrons as they move through the photosystem pigments.

Androecium

Collective term applied to all of the male (stamen) parts of the flower.

Gynoecium

Collective term for all of the carpels (or pistils) in a flower. Some flowers have many pistils that are partially or wholly fused.

Germ Cells

Collective term for cells in the reproductive organs of multicellular organisms that divide by meiosis to produce gametes.

Palisade Parenchyma

Columnar cells located just below the upper epidermis in leaves; the cells where most of the light absorption in photosynthesis occurs.

Golden Brown Algae

Common name applied to the protistan division Chrysophyta.

Green Algae

Common name for algae placed in the division Chlorophyta.

Red Algae

Common name for the algae placed in the division Rhodophyta.

White Blood Cell

Component of the blood that functions in the immune system. Also known as a leukocyte.

Red Blood Cell

Component of the blood that transports oxygen with the hemoglobin molecule.

Steroids

Compounds with a skeleton of four rings of carbon to which various side groups are attached; one of the three main classes of hormones.

Complete Flower

Condition in which all flower parts are present. Example: lily.

Incomplete Flower

Condition in which one or more "typical" flower parts are absent. Example: grass flowers such as corn tassels which are male.

Sieve Cells

Conducting cells in the phloem of vascular plants. See sieve elements

Motor Units

Consist of a motor neuron with a group of muscle fibers; form the units into which skeletal muscles are organized; enable muscles to contract on a graded basis.

Large Intestine

Consists of the cecum, appendix, colon, and rectum; absorbs some nutrients, but mainly prepares feces for elimination.

Lymph Hearts

Contractile enlargements of vessels that pump lymph back into the veins; found in fish, amphibians, and reptiles.

Ligaments

Dense parallel bundles of connective tissue that strengthen joints and hold the bones in place.

Cohesion-Adhesion Theory

Describes the properties of water that help move it through a plant. Cohesion is the ability of water molecules to stick together (held by hydrogen bonds), forming a column of water extending from the roots to the leaves; adhesion is the ability of water molecules to stick to the cellulose in plant cell walls, counteracting the force of gravity and helping to lift the column of water.

Genetic Maps

Diagrams showing the order of and distance between genes; constructed using crossover information.

Organs

Differentiated structures consisting of tissues and performing some specific function in an organism. Structures made of two or more tissues which function as an integrated unit. e.g. the heart, kidneys, liver, stomach.

Passive Transport

Diffusion across a plasma membrane in which the cell expends no energy.

Osmosis

Diffusion of water molecules across a membrane in response to differences in solute concentration. Water moves from areas of high-water/low-solute concentration to areas of low-water/high-solute concentration. Diffusion of water across a semipermeable barrier such as a cell membrane, from high water potential (concentration) to lower water potential (concentration).

Chloroplasts

Disk-like organelles with a double membrane found in eukaryotic plant cells; contain thylakoids and are the site of photosynthesis. ATP is generated during photosynthesis by chemiosmosis.

Ascomycetes

Division of fungi that contains the yeasts and morels; ascomycetes produce an ascus (or sac) in which ascospores are produced.

Bottlenecks

Drastic short-term reductions in population size caused by natural disasters, disease, or predators; can lead to random changes in the population's gene pool.

Elongation

During protein synthesis, the growth of the polypeptide chain through the addition of amino acids; the second step in translation.

Crossing-Over

During the first meiotic prophase, the process in which part of a chromatid is physically exchanged with another chromatid to form chromosomes with new allele combinations.

RNA Polymerase

During transcription, an enzyme that attaches to the promoter region of the DNA template, joins nucleotides to form the synthesized strand of RNA and detaches from the template when it reaches the terminator region.

Abiogenesis

Early theory that held that some organisms originated from nonliving material.

Monotremes

Egg-laying mammals; e.g., the spiny anteater and the duck-billed platypus.

Meristematic Tissue

Embryonic tissue located at the tips of stems and roots and occasionally along their entire length; can divide to produce new cells; one of the four main tissue systems in plants.

Radiation

Energy emitted from the unstable nuclei of radioactive isotopes.

First Law of Thermodynamics (Conservation)

Energy is neither created nor destroyed, it changes from one form to another.

Lipases

Enzymes secreted by the pancreas that are active in the digestion of fats.

Langerhans' Cells

Epidermal cells that participate in the inflammatory response by engulfing microorganisms and releasing chemicals that mobilize immune system cells.

Mesentery

Epithelial cells supporting the digestive organs.

Temperate Forest Biome

Extends across regions of the northern hemisphere with abundant rainfall and long growing seasons. Deciduous, broad-leaved trees are the dominant plants.

Trichomes

Extensions from the epidermis of the plant that provide shade and protection for the plant.

Root Hairs

Extensions of the root epidermis that increase the root's ability to absorb water.

Tundra Biome

Extensive treeless plain across northern Europe, Asia, and North American between the taiga to the south and the permanent ice to the north. Much of the soil remains frozen in permafrost, and grasses and other vegetation support herds of large grazing mammals.

Barriers to Gene Flow

Factors, such as geographic, mechanical, and behavioral isolating mechanisms that restrict gene flow between populations, leading to populations with differing allele frequencies.

Aggregates

Fairly random associations of animals with little or no internal organization; form in response to a single stimulus and disperse when the stimulus is removed; one of the three broad classes of social organization.

Growth Rings

Features of woody stems produced by plants growing in areas with seasonal (as opposed to year-long) growth. The growth ring marks the position of the vascular cambium at the cessation of the previous year's growth.

Pistil

Female reproductive structures in flowers, consisting of the stigma, style, and ovary. Also known as a carpel in some books.

Molecular Biology

Field of biology that studies the molecular level of organization.

Rhizoids

Filamentous structures in the plants group known as bryophytes that attach to a substrate and absorb moisture. The term is also applied to similar structures found outside the bryophytes.

Microtubules

Filaments about 25 nanometers in diameter found in cilia, flagella, and the cytoskeleton.

Villi

Finger-like projections of the lining of the small intestine that increase the surface area available for absorption. Also, projections of the chorion that extend into cavities filled with maternal blood and allow the exchange of nutrients between the maternal and embryonic circulations. Projections of the inner layer of the small intestine that increase the surface area for absorption of food.

Lobe-Finned

Fish with muscular fins containing large jointed bones that attach to the body; one of the two main types of bony fish.

Kingdoms

Five broad taxonomic categories (Monera, Protista, Plantae, Fungi, Animalia) into which organisms are grouped, based on common characteristics.

Angiosperms

Flowering plants. First appearing at least 110 million years ago from an unknown gymnosperm ancestor, flowering plants have risen to dominance in most of the world's floras. The male gametophyte is 2-3 cells contained within a pollen grain; the female gametophyte is usually eight cells contained within an ovule which is retained on the sporophyte phase of the plant's life cycle.

Gymnosperms

Flowerless, seed-bearing land plants; the first seed plants; living groups include the pines, ginkgos, and cycads. Naked seeds.

Urine

Fluid containing various wastes that is produced in the kidney and excreted from the bladder.

Interstitial Fluid

Fluid surrounding the cells in body tissues; provides a path through which nutrients, gases, and wastes can travel between the capillaries and the cells.

Hydrostatic Skeleton

Fluid-filled closed chambers that give support and shape to the body in organisms such as jellyfish and earthworms. Not to be confused with the water-vascular system of echinoderms.

Diatomaceous Earth

Fossilized deposits of diatoms; used for abrasives, polishes and as a filtering agent.

Coprolites

Fossilized feces.

Megaspores

Four haploid cells produced by meiosis in the ovule of a flower. Usually, three of these cells degenerate, with the remaining cell becoming the female gametophyte phase of the plant's life cycle. Large (palynologists consider the megaspores to generally be above 200 micrometers in diameter) spores that develop into the megagametophyte, which in turn produces eggs.

Microspores

Four haploid cells produced by the meiotic division in the pollen sacs of flowers or microsporangia of gymnosperms. Microspores undergo mitotic division and become encased in a thick protective wall to form pollen grains. Small, size usually less than 200 micrometers, spores produced by meiosis. Microspores either germinate into the male gametophyte or have the male gametophyte develop inside the microspore wall.

Palynomorph

Generic term for any object a palynologist studies.

Oncogenes

Genes that can activate cell division in cells that normally do not divide or do so only slowly. A gene that when overexpressed leads to cancer, but which normally functions in cell division.

Tumor Suppressor Genes

Genes that normally keep cell division under control, preventing the cell from responding to internal and external commands to divide.

Albinism

Genetic condition caused by the body's inability to manufacture pigments; an autosomal recessive trait.

Test Cross

Genetic crossing of an organism with known genotype (one that exhibits the recessive phenotype) with an individual expressing the dominant phenotype but of unknown heritage.

Ordovician Period

Geologic period of the Paleozoic Era after the Cambrian Period between 500 and 435 million years ago. Major advances during this period include the bony fish and possibly land plants (during the late Ordovician).

Cambrian

Geologic period that begins the Paleozoic Era 570 million years ago. Marked in its beginning by a proliferation of animals with hard, preservable parts, such as brachiopods, trilobites, and archaeocyathids.

Seminal Vesicles

Glands that contribute fructose to sperm. The fructose serves as an energy source. The structures that add fructose and hormones to semen.

Bulbourethral Glands

Glands that secrete a mucus-like substance that is added to sperm and provides lubrication during intercourse.

Salivary Glands

Glands that secrete saliva into the mouth.

Transforming Factor

Griffith's name for the unknown material leading to transformation; later found to be DNA.

Mammal-Like Reptiles

Group of Permian-Triassic reptiles having some possible mammalian features, notably a more prominent dentary (tooth-bearing) bone and reduction of the incus and malleus (which are part of the reptilian jaw along with the dentary). The mammal-like reptiles are thought to have been the reptile group from which the mammals later evolved.

Cycads

Group of gymnosperm seed plants that have large fern-like leaves and reproduce by cones but not flowers.

Conifers

Group of gymnosperms that reproduce by cones and have needle-like leaves (in general); includes the pines.

Vascular Plants

Group of plants having lignified conducting tissue (xylem vessels or tracheids).

Gnetales

Group of seed plants restricted to three genera today (Gnetum, Ephedra, and Welwitschia); the possible outgroup for flowering plants.

Ginkgos

Group of seed plants today restricted to a single genus (Ginkgo biloba); ginkgos were more diverse during the Mesozoic Era.

Organ Systems

Groups of organs that perform related functions.

Tissues

Groups of similar cells organized to carry out one or more specific functions. Groups of cells performing a function in a multicellular organism.

Vascular Bundle

Groups of xylem, phloem and cambium cells in stems of plants descended from the procambium embryonic tissue layer.

Cilia

Hair-like organelles extending from the membrane of many eukaryotic cells; often function in locomotion (sing.: cilium).

Microvilli

Hair-like projections on the surface of the epithelial cells of the villi in the small intestine; increase the surface area of the intestine to improve absorption of digested nutrients.

Gametes

Haploid reproductive cells (ovum and sperm).

Homozygous

Having identical alleles for a given gene.

Hemizygous

Having one or more genes that have no allele counterparts. Usually applied to genes on the male's X chromosome (in humans).

Abnormal Hemoglobin

Hemoglobin molecule with a different shape due to an altered amino acid sequence (ultimately caused by an altered DNA base sequence), such as in the inherited disease sickle-cell anemia.

Hypertension

High blood pressure; blood pressure consistently above 140/90.

Neurons

Highly specialized cells that generate and transmit bioelectric impulses from one part of the body to another; the functional unit of the nervous system. A cell of the nerve tissue having a cell body input zone of dendrites and an output zone of an axon (of varying length). The electrochemical nerve impulse/message is transmitted by neurons.

"One Gene, One Enzyme" Hypothesis

Holds that a single gene controls the production, specificity, and activity of each enzyme in a metabolic pathway. Thus, mutation of such a gene changes the ability of the cell to carry out a particular reaction and disrupts the entire pathway.

Chromosome Theory of Inheritance

Holds that chromosomes are the cellular components that physically contain genes; proposed in 1903 by Walter Sutton and Theodore Boveri.

Out of Africa Hypothesis

Holds that modern human populations (Homo sapiens) are all derived from a single speciation event that took place in a restricted region in Africa.

Law of the Minimum

Holds that population growth is limited by the resource in shortest supply.

Tropic Hormone

Hormone made by one gland that causes another gland to secrete a hormone.

Gonadotropins

Hormones produced by the anterior pituitary that affect the testis and ovary; include follicle-stimulating hormone and luteinizing hormone.

Sickle Cell Anemia

Human autosomal recessive disease that causes production of abnormal red blood cells that collapse (or sickle) and cause circulatory problems.

Brachydactly

Human genetic disorder that causes production of an extra digit; an autosomal dominant trait. Sometimes referred to as polydactyly.

Asteroid Impacts

Hypothesis that links certain mass extinction events with the impact of a comet or asteroid, most notably the mass extinction 65 million years that caused the disappearance of dinosaurs and many other reptilian groups. Asteroid impacts early in earth history also contributed to the formation of the atmosphere and oceans.

Lyon Hypothesis

Idea proposed by Mary Lyon that mammalian females inactivate one or the other X-chromosome during early embryogenesis. This deactivated chromosome forms the Barr body.

Cell-Mediated Immunity

Immune reaction directed against body cells that have been infected by viruses and bacteria; controlled by T cells.

Antibody-Mediated Immunity

Immune reaction that protects primarily against invading viruses and bacteria through antibodies produced by plasma cells; also known as humoral immunity.

Spores

Impervious structures formed by some cells that encapsulate the cells and protect them from the environment; haploid cells that can survive unfavorable conditions and germinate into new haploid individuals or act as gametes in fertilization.

DNA Polymerase

In DNA replication, the enzyme that links the complementary nucleotides together to form the newly synthesized strand.

Rhizome

In ferns, a horizontal stem with upright leaves containing vascular tissue.

Prothallus

In ferns, a small heart-shaped bisexual gametophyte.

Zygospore

In fungi, a structure that forms from the diploid zygote created by the fusion of haploid hyphae of different mating types. After a period of dormancy, the zygospore forms sporangia, where meiosis occurs and spores form.

Monohybrid Cross

In genetics, a cross that involves only one characteristic.

Dihybrid Cross

In genetics, a cross that involves two sets of characteristics.

Turner Syndrome

In humans, a genetically determined condition in which an individual has only one sex chromosome (an X). Affected individuals are always female and are typically short and infertile.

Klinefelter Syndrome

In humans, a genetically determined condition in which the individual has two X and one Y chromosome. Affected individuals are male and typically tall and infertile.

Pectoral Girdle

In humans, the bony arch by which the arms are attached to the rest of the skeleton; composed of the clavicle and scapula.

Pelvic Girdle

In humans, the bony arch by which the legs are attached to the rest of the skeleton; composed of the two hip bones.

Trachea

In insects and spiders, a series of tubes that carry air directly to cells for gas exchange; in humans, the air-conducting duct that leads from the pharynx to the lungs.

Sleep Movement

In legumes, the movement of the leaves in response to daily rhythms of dark and light. The leaves are horizontal in daylight and folded vertically at night.

Ejaculatory Duct

In males, a short duct that connects the vas deferens from each testis to the urethra.

Scrotum

In mammals, a pouch of skin located outside the body cavity into which the testes descend; provides proper temperature for the testes.

Thorax

In many arthropods, one of three regions formed by the fusion of the segments (others are the head and abdomen).

Mantle

In mollusks, a membranous or muscular structure that surrounds the visceral mass and secretes a shell if one is present.

Internal Environment

In multicellular organisms, the aqueous environment that is outside the cells but inside the body.

Pseudocoelom

In nematodes, a closed fluid-containing cavity that acts as a hydrostatic skeleton to maintain body shape, circulate nutrients, and hold the major body organs.

Ovule

In seed plants, a protective structure in which the female gametophyte develops, fertilization occurs, and seeds develop; contained within the ovary. Structures inside the ovary of the flower within which the female gametophyte develops after megasporogenesis has produced a megaspore inside each ovule.

Quaternary Structure

In some proteins, a fourth structural level created by interactions with other proteins. Aspect of protein structure determined by the number and arrangement of polypeptides in a large protein such as hemoglobin.

Secondary Cell Wall

In woody plants, a second wall inside the primary cell wall; it contains alternating layers of cellulose and lignin.

Barr Body

Inactivated X-chromosome in mammalian females. Although inactivated, the Barr body is replicated prior to cell division and thus is passed on to all descendant cells of the embryonic cell that had one of its X-chromosomes inactivated.

Prions

Infectious agents composed only of one or more protein molecules without any accompanying genetic information.

Virus

Infectious chemical agent composed of a nucleic acid (DNA or RNA) inside a protein coat.

Viroids

Infective forms of nucleic acid without a protective coat of protein; unencapsulated single-stranded RNA molecules. Naked RNA, possibly of degenerated virus, that infects plants.

Precambrian

Informal term describing 7/8 of geologic time from the beginning of the earth to the beginning of the Cambrian Period of the Paleozoic Era. During this time the atmosphere and oceans formed, life originated (or possibly "colonized" Earth), eukaryotes and simple animals evolved and by the end of the precambrian they began to accumulate hard preservable parts, the common occurrence of which marks the beginning of the Cambrian.

Heartwood

Inner rings of xylem that have become clogged with metabolic by-products and no longer transport water; visible as the inner darker areas in the cross section of a tree trunk.

Steinkerns

Internal casts of a fossil. Steinkerns may reveal internal anatomy of an organism, such as muscle attachment, and other details of soft tissue structure.

Lymph

Interstitial fluid in the lymphatic system.

Ice Age

Interval of geologic time between 2 million and 10,000 years ago during which the northern hemisphere experienced several episodes of continental glacial advance and retreat along with a climatic cooling. The icing over of Antarctica was also completed during this time.

Peristalsis

Involuntary contractions of the smooth muscles in the walls of the esophagus, stomach, and intestines that propel food along the digestive tract. Waves of muscle contraction in the esophagus that propel food from the oral cavity to the stomach.

Tight Junctions

Junctions between the plasma membranes of adjacent cells in animals that form a barrier, preventing materials from passing between the cells.

Gap Junctions

Junctions between the plasma membranes of animal cells that allow communication between the cytoplasm of adjacent cells.

Plasmodesmata

Junctions in plants that penetrate cell walls and plasma membranes, allowing direct communication between the cytoplasm of adjacent cells (sing.: plasmodesma).

Inheritance of Acquired Characteristics

Lamarck's view that features acquired during an organism's lifetime would be passed on to succeeding generations, leading to inheritable change in species over time.

Macromolecules

Large molecules made up of many small organic molecules that are often referred to as monomers; e.g., carbohydrates, lipids, proteins, and nucleic acids. Macromolecules are polymers of monomers.

Mesophyll

Layer of leaf tissue between the epidermis layers; literally meaning "middle of the leaf".

Palisade

Layer of mesophyll cells in leaves that are closely placed together under the epidermal layer of the leaf.

Sapwood

Layers of secondary xylem that are still functional in older woody plants; visible as the outer lighter areas in the cross section of a tree trunk.

Myelin Sheath

Layers of specialized glial cells, called Schwann cells, that coat the axons of many neurons.

Rods

Light receptors in primates' eyes that provide vision in dim light.

Polysaccharides

Long chains of monosaccharide units bonded together; e.g., glycogen, starch, and cellulose.

Polynucleotides

Long chains of nucleotides formed by chemical links between the sugar and phosphate groups.

Axons

Long fibers that carry signals away from the cell body of a neuron.

Muscle Fibers

Long, multinucleated cells found in skeletal muscles; made up of myofibrils. One of the four major groups of vertebrate cell/tissue types. Muscle cells contract/relax, allowing movement of and/or within the animal.

Tracheids

Long, tapered cells with pitted walls that form a system of tubes in the xylem and carry water and solutes from the roots to the rest of the plant. One type of xylem cells. Tracheids are long and relatively narrow, and transport materials from the roots upward. Tracheids are dead at maturity and have lignin in their secondary walls.

Flagella

Long, whip-like locomotion organelles found in both prokaryotic and eukaryotic cells; sing.: flagellum. Eukaryotic flagella have an internal arrangement of microtubules in a 9 + 2 array.

B Memory Cells

Long-lived B cells that are produced after an initial exposure to an antigen and play an important role in secondary immunity. They remain in the body and facilitate a more rapid response if the antigen is encountered again.

Sediment

Loose aggregate of solids derived from preexisting rocks, or solids precipitated from solution by inorganic chemical processes or extracted from solution by organisms.

Adenosine Diphosphate (ADP)

Lower energy form of ATP, having two (instead of the three in ATP) phosphate groups attached to the adenine base and ribose sugar.

Carotenoids

Major group of accessory pigments in plants; includes beta carotene.

Testosterone

Male sex hormone that stimulates sperm formation, promotes the development of the male duct system in the fetus, and is responsible for secondary sex characteristics such as facial hair growth.

Osmoconformers

Marine organisms that have no system of osmoregulation and must change the composition of their body fluids as the composition of the water changes; include invertebrates such as jellyfish, scallops, and crabs.

Osmoregulators

Marine vertebrates whose body fluids have about one-third the solute concentration of seawater; must therefore undergo osmoregulation.

Sporozoans

Members of the protists that are referred to as slime molds; may include organisms resembling the ancestors of fungi.

Vacuoles

Membrane-bound fluid-filled spaces in plant and animal cells that remove waste products and store ingested food.

Plastids

Membrane-bound organelles in plant cells that function in storage (of food or pigments) or food production. Term for any double membrane-bound organelle. Chloroplasts contain the chemicals for photosynthesis, amyloplasts (also known as leucoplasts) store starch, chromoplasts contain colorful pigments such as in the petals of a flower or epidermis of a fruit.

Peroxisomes

Membrane-bound vesicles in eukaryotic cells that contain oxidative enzymes.

Lysosomes

Membrane-enclosed organelles containing digestive enzymes. The lysosomes fuse with food vacuoles and enzymes contained within the lysosome chemically breakdown and/or digest the food vacuole's contents.

Fontanels

Membranous areas in the human cranial bones that do not form bony structures until the child is 14 to 18 months old; known as "soft spots."

Principle of Segregation

Mendel's first law. Holds that each pair of factors of heredity separate during gamete formation so that each gamete receives one member of a pair.

Principle of Independent Assortment

Mendel's second law. Holds that during gamete formation, alleles in one gene pair segregate into gametes independently of the alleles of other gene pairs. As a result, if enough gametes are produced, the collective group of gametes will contain all combinations of alleles possible for that organism.

Somites

Mesodermal structures formed during embryonic development that give rise to segmented body parts such as the muscles of the body wall.

Jurassic Period

Middle period of the Mesozoic Era, between 185-135 million years ago. Characterized by the (possible) origin of angiosperms and the continued split of the worldwide supercontinent of Pangaea.

Petrifaction

Mode of fossilization where f organic matter is replaced with silica.

Sliding Filament Model

Model of muscular contraction in which the actin filaments in the sarcomere slide past the myosin filaments, shortening the sarcomere and therefore the muscle.

Quantum Models of Speciation

Models of evolution that hold that speciation sometimes occurs rapidly as well as over long periods, as the classical theory proposed.

Sepals

Modified leaves that protect a flower's inner petals and reproductive structures. Small, leaf-like structures in flowers that enclose and protect the developing flower. These are often green, but in many monocots they are the same color as the petals (in which case the term tepal is applied since sepals and petals look so much alike).

Laurentia

Name applied to the "core" of North America in the times from the breakup of the precambrian supercontinent Rodinia to the formation of Pangaea.

Gondwana

Name applied to the ancient (Paleozoic-early Mesozoic) southern hemisphere supercontinent that rifted apart to form present-day Antarctica, India, Africa, Australia, and South America. The southern part of Pangaea.

Nectaries

Nectar-secreting organs in flowering plants that serve as insect feeding stations and thus attract insects, which then assist in the transfer of pollen.

Spicules

Needle-shaped skeletal elements in sponges that occur in the matrix between the epidermal and collar cells.

Sensory Neurons

Neurons that carry signals from receptors and transmit information about the environment to processing centers in the brain and spinal cord. Neurons carrying messages from sensory receptors to the spinal cord. Sometimes referred to as an afferent neuron.

Interneurons

Neurons that process signals from one or more sensory neurons and relay signals to motor neurons. Aka connector neurons.

Motor Neurons

Neurons that receive signals from interneurons and transfer the signals to effector cells that produce a response. Nerve cells connected to a muscle or gland. Sometimes also known as effector neurons.

Recombinant DNA Molecules

New combinations of DNA fragments formed by cutting DNA segments from two sources with restriction enzyme and then joining the fragments together with DNA ligase. Interspecies transfer of genes usually through a vector such as a virus or plasmid.

Glial Cells

Nonconducting cells that serve as support cells in the nervous system and help to protect neurons.

Vestigial Structures

Nonfunctional remains of organs that were functional in ancestral species and may still be functional in related species; e.g., the dewclaws of dogs.

Fungi

Nonmobile, heterotrophic, mostly multicellular eukaryotes, including yeasts and mushrooms.

Ribonucleic Acid (RNA)

Nucleic acid containing ribose sugar and the base Uracil; RNA functions in protein synthesis. The single stranded molecule transcribed from one strand of the DNA. There are three types of RNA, each is involved in protein synthesis. RNA is made up of nucleotides containing the sugar ribose, a phosphate group, and one of four nitrogenous bases (adenine, uracil, cytosine or guanine).

Grasslands Biome

Occurs in temperate and tropical regions with reduced rainfall or prolonged dry seasons; characterized by deep, rich soil, an absence of trees, and large herds of grazing animals.

Mycorrhiza

Occurs when a fungus (basidiomycete or zygomycete) weaves around or into a plant's roots and forms a symbiotic relationship. Fungal hyphae absorb minerals from the soil and pass them on to the plant roots while the fungus obtains carbohydrates from the plant (pl.: mycorrhizae).

Predatory Release

Occurs when a predator species is removed from a prey species such as by great reduction in the predator's population size or by the migration of the prey species to an area without major predators. The removal of the predator releases the prey from one of the factors limiting its population size.

Polygenic Inheritance

Occurs when a trait is controlled by several gene pairs; usually results in continuous variation.

Positive Feedback Control

Occurs when information produced by the feedback increases and accelerates the response.

Negative Feedback Control

Occurs when information produced by the feedback reverses the direction of the response; regulates the secretion of most hormones.

Competitive Release

Occurs when one of two competing species is removed from an area, thereby releasing the remaining species from one of the factors that limited its population size.

True-Breeding

Occurs when self-fertilization gives rise to the same traits in all offspring, generation after generation. Now interpreted as equivalent to homozygous.

Discontinuous Variation

Occurs when the phenotypes of traits controlled by a single gene can be sorted into two distinct phenotypic classes.

Continuous Variation

Occurs when the phenotypes of traits controlled by a single gene cannot be sorted into two distinct phenotypic classes, but rather fall into a series of overlapping classes.

Catastrophism

Once-popular belief that events in earth history had occurred in the past were sudden events and by processes unlike those operating today. Periods of catastrophic change were followed by long periods of little change. A subgroup, the Diluvialists, contended that Noah's Flood was the last of many floods which had occurred throughout earth's history.

Cardiac Cycle

One heartbeat; consists of atrial contraction and relaxation, ventricular contraction and relaxation, and a short pause.

Endocrine System

One of eleven major body organ systems in animals; a system of glands that works with the nervous system in controlling the activity of internal organs, especially the kidneys, and in coordinating the long-range response to external stimuli.

Muscular System

One of eleven major body organ systems in animals; allows movement and locomotion, powers the circulatory, digestive, and respiratory systems, and plays a role in regulating temperature.

Digestive System

One of eleven major body organ systems in animals; converts food from the external environment into nutrient molecules that can be used and stored by the body and eliminates solid wastes; involves five functions: movement, secretion, digestion, absorption, and elimination.

Nervous System

One of eleven major body organ systems in animals; coordinates and controls actions of internal organs and body systems, receives and processes sensory information from the external environment, and coordinates short-term reactions to these stimuli

Reproductive System

One of eleven major body organ systems in animals; is responsible for reproduction and thus the survival of the species.

Respiratory System

One of eleven major body organ systems in animals; moves oxygen from the external environment into the internal environment and removes carbon dioxide from the body.

Skeletal System

One of eleven major body organ systems in animals; supports the body, protects internal organs, and, with the muscular system, allows movement and locomotion.

Skin

One of eleven major body organ systems in animals; the outermost layer protecting multicellular animals from the loss or exchange of internal fluids and from invasion by foreign microorganisms; composed of two layers: the epidermis and dermis.

Circulatory System

One of eleven major body organ systems in animals; transports oxygen, carbon dioxide, nutrients, and waste products between cells and the respiratory system and carries chemical signals from the endocrine system; consists of the blood, heart, and blood vessels.

Excretory System

One of eleven major body systems in animals; regulates the volume and molecular and ionic constitution of internal body fluids and eliminates metabolic waste products from the internal environment.

Predation

One of the biological interactions that can limit population growth; occurs when organisms kill and consume other living organisms.

Competition

One of the biological interactions that can limit population growth; occurs when two species vie with each other for the same resource.

Tube Nucleus

One of the cells in the male gametophyte in seed plants. The tube nucleus grows through the stigma, style, and into the ovule, clearing the way for the sperm nuclei to enter the embryo sac.

Blood Group or Type

One of the classes into which blood can be separated on the basis of the presence or absence of certain antigens; notably, the ABO types and the Rh blood group.

Zygomycetes

One of the divisions of the fungi, characterized by the production of zygospores, includes the bread molds.

Immune System

One of the eleven major body organ systems in vertebrates; defends the internal environment against invading microorganisms and viruses and provides defense against the growth of cancer cells.

Community Age

One of the factors that helps cause the latitudinal diversity gradient. Tropical communities have had more time to evolve because they have been less disrupted by advancing ice sheets and other relatively recent climatic changes.

Cell Theory

One of the four (or five) unifying concepts in biology. The cell theory states that all living things are composed of at least one cell and that the cell is the fundamental unit of function in all organisms. Corollaries: the chemical composition of all cells is fundamentally alike; all cells arise from preexisting cells through cell division.

Lipids

One of the four classes of organic macromolecules. Lipids function in the long-term storage of biochemical energy, insulation, structure and control. Examples of lipids include the fats, waxes, oils and steroids (e.g. testosterone, cholesterol).

Adenine

One of the four nitrogen-containing bases occurring in nucleotides, the building blocks of the organic macromolecule group known as nucleic acids (DNA and RNA). Adenine is also the base in the energy carrying molecule ATP (adenosine triphosphate) which is the energy coin of the cell.

Purine

One of the groups of nitrogenous bases that are part of a nucleotide. Purines are adenine and guanine, and are double-ring structures.

Pyrimidine

One of the groups of nitrogenous bases that are part of a nucleotide. Pyrimidines are single ringed, and consist of the bases thymine (in DNA), uracil (replacing thymine in RNA), and cytosine.

Eras

One of the major divisions of the geologic time scale.

Guanine

One of the nitrogenous bases in nucleic acids, guanine is one of the two purine bases.

Stability

One of the phases of a population's life cycle. The population's size remains roughly constant, fluctuating around some average density. Also, the ability of a community to persist unchanged.

Thymine

One of the pyrimidine bases in DNA, thymine is replaced by uracil in RNA.

Cytosine

One of the pyrimidine nitrogenous bases occurring in both DNA and RNA.

Incus

One of the three bones comprising the middle ear of mammals.

Stapes

One of the three bones that function in hearing.

Parenchyma

One of the three major cell types in plants. Parenchyma cells have thin, usually multi sided walls, are unspecialized but carry on photosynthesis and cellular respiration and can store food; form the bulk of the plant body; found in the fleshy tissue of fruits and seeds, photosynthetic cells of leaves, and the vascular system. Generalized plant cells whose numerous functions include photosynthesis, storage, bulk of herbaceous stem tissues, lateral transport in woody stems. Parenchyma are variously shaped but are characterized by thin walls and remain alive at functional maturity.

Collenchyma

One of the three major cell types in plants; are elongated and have thicker walls than parenchyma cells and are usually arranged in strands; provide support and are generally in a region that is growing.

Sclerenchyma

One of the three major cell types in plants; have thickened, rigid, secondary walls that are hardened with lignin; provide support for the plant. Sclerenchyma cells include fibers and sclereids. Plant tissue type consisting of elongated cells with thickened secondary walls for support of the plant.

Ribosomal RNA

One of the three types of RNA; rRNA is a structural component in ribosomes.

Pelagic Zone

One of the two basic subdivisions of the marine biome; consists of the water above the sea floor and its organisms.

Benthic Zone

One of the two basic subdivisions of the marine biome; includes the sea floor and bottom-dwelling organisms.

Progesterone

One of the two female reproductive hormones secreted by the ovaries.

Dermis

One of the two layers of skin; a connective tissue layer under the epidermis containing elastic and collagen fibers, capillary networks, and nerve endings.

Dicots

One of the two main types of flowering plants; characterized by having two cotyledons, floral organs arranged in cycles of four or five, and leaves with reticulate veins; include trees (except conifers) and most ornamental and crop plants.

Monocots

One of the two major types of flowering plants; characterized by having a single cotyledon, floral organs arranged in threes or multiples of three, and parallel-veined leaves; include grasses, cattails, lilies, and palm trees. One of the two major groups in the Angiosperms, monocots are characterized by having a single seed leaf (cotyledon), flower parts in 3's or multiples of 3, mono aperture pollen (although some dicots also have this feature), parallel veins in their leaves, and scattered vascular bundles in their stems.

Absolute Time

One of the two types of geologic time (relative time being the other), with a definite age date established mostly by the decay of radioactive elements, although ages may also be obtained by counting tree rings, decay of a specific type of atom, or annual sedimentary layers (such as varves in lakes or layers in a glacier). The term is in some disfavor because it suggests an exactness that may not be possible to obtain.

Placental Mammals

One of three groups of mammals that carry their young in the mother's body for long periods during which the fetus is nourished by the placenta. Humans are placental mammals.

Termination Codon

One of three three-base sequences that initiate termination of the protein synthesis process. See stop codon.

Species

One or more populations of interbreeding or potentially interbreeding organisms that are reproductively isolated in nature from all other organisms. Populations of individuals capable of interbreeding and producing viable, fertile offspring. The least inclusive taxonomic category commonly used.

Gill Slits

Opening or clefts between the gill arches in fish. Water taken in by the mouth passes through the gill slits and bathes the gills. Also, rudimentary grooves in the neck region of embryos of air-breathing vertebrates such as humans; a characteristic of chordates.

Nuclear Pores

Openings in the membrane of a cell's nuclear envelope that allow the exchange of materials between the nucleus and the cytoplasm.

Contractile Vacuole

Organelle in many eukaryotes that acts as a bilge pump in the active transport of excess water from the cell.

Golgi Complex

Organelles in animal cells composed of a series of flattened sacs that sort, chemically modify, and package proteins produced on the rough endoplasmic reticulum.

Dictyosomes

Organelles in plant cells composed of a series of flattened membrane sacs that sort, chemically modify, and package proteins produced on the rough endoplasmic reticulum. Also known as the Golgi Apparatus.

Polymer

Organic molecule composed of smaller units known as monomers. A large molecule composed of smaller subunits, for example starch is a polymer of glucose, proteins are polymers of amino acids.

Carbohydrates

Organic molecules composed of carbon, hydrogen, and oxygen that serve as energy sources and structural materials for cells of all organisms.

Chemotrophs

Organisms (usually bacteria) that derive energy from inorganic reactions; also known as chemosynthetic.

Multicellular

Organisms composed of multiple cells and exhibiting some division of labor and specialization of cell structure and function.

Filter Feeders

Organisms such as sponges that feed by removing food from water that filters through their body.

Parasites

Organisms that live in, with, or on another organism. The parasites benefit from the association without contributing to the host, usually they cause some harm to the host.

Saprophytes

Organisms that obtain their nutrients from decaying plants and animals. Saprophytes are important in recycling organic material.

Heterotrophs

Organisms that obtain their nutrition by breaking down organic molecules in foods; include animals and fungi.

Autotrophs

Organisms that synthesize their own nutrients; include some bacteria that are able to synthesize organic molecules from simpler inorganic compounds.

Phototrophs

Organisms that use sunlight to synthesize organic nutrients as their energy source; e.g., cyanobacteria, algae, and plants.

Roots

Organs, usually occurring underground, that absorb nutrients and water and anchor the plant; one of the three major plant organ systems.

Plasmolysis

Osmotic condition in which a cell loses water to its outside environment.

Exine

Outer covering of pollen grains, often containing sporopollenin, an acid-resistant polysaccharide that allows pollen grains to become fossils.

Spongy Mesophyll

Parenchyma cells found in plant leaves that are irregularly shaped and have large intercellular spaces.

Style

Part of the female reproductive structure in the carpel of a flower; formed from the ovary wall. The tip of the style carries the stigma to which pollen grains attach. Part of the pistil that separates the stigma from the ovary.

Stigma

Part of the female reproductive structure of the carpel of a flower; the sticky surface at the tip of the style to which pollen grains attach. The receptive surface of the pistil (of the flower) on which pollen is placed by a pollinator.

Diencephalon

Part of the forebrain; consists of the thalamus and hypothalamus.

Intracellular Route

Path taken by water through the cells of the root between the epidermis and the xylem, moving through plasmodesmata.

Extracellular Route

Path taken by water through the root in which water moves through the spaces between cell walls of the cortex parenchyma.

Reflex Arc

Pathway of neurons, effector(s) and sensory receptors that participate in a reflex.

Homeobox Genes

Pattern genes that establish the body plan and position of organs in response to gradients of regulatory molecules.

Devonian

Period of geologic time from 410 - 360 million years before the present. Life on land diversified, with the amphibians appearing late in this period. Plants underwent major changes, including the development of forests and seeds. In the water, fish diversified into all modern groups as well as numerous now-extinct forms.

Gestation

Period of time between fertilization and birth of an animal. Commonly called pregnancy.

Root System

Plant organ systems that anchors the plant in place, stores excess sugars, and absorbs water and mineral nutrients. That part of the plant is below ground level.

Secondary Compounds

Plant products that are not important in metabolism but serve other purposes, such as attracting animals for pollination or killing parasites.

Ground System

Plant tissue system, composed mainly of parenchyma cells with some collenchyma and sclerenchyma cells, that occupies the space between the epidermis and the vascular system; is involved in photosynthesis, water and food storage, and support; one of the four main tissue systems in plants.

Nonvascular Plants

Plants lacking lignified vascular tissue (xylem), vascularized leaves, and having a free-living, photosynthetic gametophyte stage that dominates the life cycle. Common examples are the mosses and liverworts.

Short-Day Plants

Plants that flower during early spring or fall when nights are relatively long and days are short; e.g., poinsettia and dandelions.

Long-Day Plants

Plants that flower in the summer when nights are short and days are long; e.g., spinach and wheat.

Perennials

Plants that persist in the environment for more than one year (as in the case of annuals).

Thigmotropism

Plants' response to contact with a solid object; e.g., tendrils' twining around a pole. Plant response to touch.

Geotropism

Plants' response to gravity: roots grow downward, showing positive geotropism, while shoots grow upward in a negative response.

Nucleic Acids

Polymers composed of nucleotides; e.g., DNA and RNA.

Proteins

Polymers made up of amino acids that perform a wide variety of cellular functions. One of the classes of organic macromolecules that function as structural and control elements in living systems. Proteins are polymers of amino acids linked together by peptide bonds.

Proteinoids

Polymers of amino acids formed spontaneously from inorganic molecules; have enzyme-like properties and can catalyze chemical reactions.

Glycogen

Polysaccharide consisting of numerous monosaccharide glucoses linked together. The animal equivalent of starch.

Glycolipids

Polysaccharides formed of sugars linked to lipids, a part of the cell membrane. Glycolysis: The universal cellular metabolic process in the cell's cytoplasm where 6-carbon glucose is split into two 3-carbon pyruvate molecules, and some ATP and NADH are produced.

Glycoproteins

Polysaccharides formed of sugars linked to proteins. On the outer surface of a membrane, they act as receptors for molecular signals originating outside the cell.

Sieve Plates

Pores in the end walls of sieve elements that connect the sieve elements together. The end walls of sieve tube cells that are perforated (sieves).

Stomata

Pores on the underside of leaves that can be opened or closed to control gas exchange and water loss. Openings in the epidermis (usually of the leaf) that allow gas exchange.

Marsupials

Pouched mammals. The young develop internally, but are born while in an embryonic state and remain in a pouch on the mother's abdomen until development is complete; this group includes kangaroos, koalas, and opossums. One of the three reproductive "strategies" of living mammals g-laying and placental being the other two), marsupials finish development in a pouch or under hairy coverings attached to the mother.

Turgor Pressure

Pressure caused by the cytoplasm pressing against the cell wall.

Osmotic Pressure

Pressure generated by water moving by osmosis into or out of a cell.

Hominoid

Primate group that includes common ancestors of humans and apes.

Hominid

Primate group that includes humans and all fossil forms leading to man only.

Replication

Process by which DNA is duplicated prior to cell division.

Semiconservative Replication

Process of DNA replication in which the DNA helix is unwound and each strand serves as a template for the synthesis of a new complementary strand, which is linked to the old strand. Thus, one old strand is retained in each new molecule.

Reverse Transcription

Process of transcribing a single-stranded DNA from a single-stranded RNA (the reverse of transcription); used by retroviruses as well as in biotechnology.

Pilus

Projection from surface of a bacterial cell (F+) that can donate genetic material to another (F-).

Monera

Prokaryotic kingdom that includes (in the most widely accepted classification system) archaebacteria, eubacteria, and cyanobacteria. Members of this kingdom were among the first forms of life over 3.5 billion years ago.

Dystrophin

Protein making up only 0.002% of all protein in skeletal muscle but which appears vital for proper functioning of the muscle. Sufferers of muscular dystrophy appear to lack dystrophin.

Enzymes

Protein molecules that act as catalysts in biochemical reactions.

Receptor

Protein on or protruding from the cell surface to which select chemicals can bind. The opiate receptor in brain cells allows both the natural chemical as well as foreign (opiate) chemicals to bind.

Histone Proteins

Proteins associated with DNA in eukaryotic chromosomes.

Antibodies

Proteins produced by immune system cells that bind to foreign molecules and microorganisms and inactivate them.

Interferons

Proteins released by cells in response to viral infection; activate the synthesis and secretion of antiviral proteins.

Chrysophytes

Protist division that is referred to as the golden brown algae; includes the diatoms.

Slime Molds

Protists that may represent a transition between protists and fungi.

Genetic Drift

Random changes in the frequency of alleles from generation to generation; especially in small populations, can lead to the elimination of a particular allele by chance alone.

Catabolic Reactions

Reactions in cells in which existing chemical bonds are broken and molecules are broken down; generally produce energy, involve oxidation, and lead to a decrease in atomic order.

Anabolic Reactions

Reactions in cells in which new chemical bonds are formed and new molecules are made; generally require energy, involve reduction, and lead to an increase in atomic order.

Erythrocytes

Red blood cells; doubly concave, enucleated cells that transport oxygen in the blood.

Dominant

Refers to an allele of a gene that is always expressed in heterozygotes.

Recessive

Refers to an allele of a gene that is expressed when the dominant allele is not present. An allele expressed only in homozygous form, when the dominant allele is absent.

Anaerobic

Refers to organisms that are not dependent on oxygen for respiration.

Bioluminescent

Refers to organisms that emit light under certain conditions.

Autotrophic

Refers to organisms that synthesize their nutrients and obtain their energy from inorganic raw materials.

Heterotrophic

Refers to organisms, such as animals, that depend on preformed organic molecules from the environment (or another organism) as a source of nutrients/energy.

Root-Leaf-Vascular System Axis

Refers to the arrangement in vascular plants in which the roots anchor the plant and absorb water and nutrients, the leaves carry out photosynthesis, and the vascular system connects the roots and leaves, carrying water and nutrients to the leaves and carrying sugars and other products of photosynthesis from the leaves to other regions of the plant.

Somatic

Relating to the non-gonadal tissues and organs of an organism's body.

Segments

Repeating units in the body parts of some animals.

Secondary Immunity

Resistance to an antigen the second time it appears. Because of the presence of B and T memory cells produced during the first exposure to the antigen, the second response is faster and more massive and lasts longer than the primary immune response.

Orgasm

Rhythmic muscular contractions of the genitals (sex organs) combined with waves of intense pleasurable sensations; in males, results in the ejaculation of semen.

Microfilaments

Rods composed of actin that are found in the cytoskeleton and are involved in cell division and movement.

Adventitious Roots

Roots that develop from the stem following the death of the primary root. Branches from the adventitious roots form a fibrous root system in which all roots are about the same size; occur in monocots.

Lungs

Sac-like structures of varying complexity where blood and air exchange oxygen and carbon dioxide; connected to the outside by a series of tubes and a small opening. In humans, the lungs are situated in the thoracic cavity and consist of the internal airways, the alveoli, the pulmonary circulatory vessels, and elastic connective tissues.

Tectonic Plates

Segments of the lithosphere that comprise the surface of the Earth much the way a turtle shell is composed of its plates.

Vectors

Self-replicating DNA molecules that can be joined with DNA fragments to form recombinant DNA molecules.

Mitochondria

Self-replicating membrane-bound cytoplasmic organelles in most eukaryotic cells that complete the breakdown of glucose, producing NADH and ATP (singular term: mitochondrion). The powerhouse of the cell. Organelles within eukaryotes that generate (by chemiosmosis) most of the ATP the cell needs to function and stay alive.

Plasmids

Self-replicating, circular DNA molecules found in bacterial cells; often used as vectors in recombinant DNA technology. Small circles of double-stranded DNA found in some bacteria. Plasmids can carry from four to 20 genes. Plasmids are a commonly used vector in recombinant DNA studies.

Feces

Semisolid material containing undigested foods, bacteria, bilirubin, and water that is produced in the large intestine and eliminated from the body.

Meissner's Corpuscles

Sensory receptors concentrated in the epidermis of the fingers and lips that make these areas very sensitive to touch.

Pacinian Corpuscles

Sensory receptors located deep in the epidermis that detect pressure and vibration.

Geographic Isolation

Separation of populations of a species by geographic means (distance, mountains, rivers, oceans, etc.) that lead to reproductive isolation of those populations.

Segregation

Separation of replicated chromosomes to opposite sides of the cell. Distribution of alleles on chromosomes into gametes during meiosis.

Calvin Cycle (aka Calvin-Benson Cycle or Carbon Fixation)

Series of biochemical, enzyme-mediated reactions during which atmospheric carbon dioxide is reduced and incorporated into organic molecules, eventually some of this forms sugars. In eukaryotes, this occurs in the stroma of the chloroplast.

Peptides

Short chains of amino acids.

Aster

Short fibers produced by cells during mitosis and meiosis. These radiate from the centriole (if it is present).

Dendrites

Short, highly branched fibers that carry signals toward the cell body of a neuron.

Vessel Elements

Short, wide cells arranged end to end, forming a system of tubes in the xylem that moves water and solutes from the roots to the rest of the plant. Large diameter cells of the xylem that are extremely specialized and efficient at conduction. An evolutionary advance over tracheids. Most angiosperms have vessels.

Monosaccharides

Simple carbohydrates, usually with a five- or six-carbon skeleton; e.g., glucose and fructose. A carbohydrate composed of a single sugar unit, such as glucose, ribose, deoxyribose, etc.

Protists

Single-celled organisms; a type of eukaryote. Protista

Protozoa

Single-celled protists grouped by their method of locomotion. This group includes Paramecium, Amoeba, and many other commonly observed protists.

Foraminifera

Single-celled protists that secrete a shell or test. Accumulations of the shells of dead foraminifera and other microscopic sea creatures form chalk deposits.

Dinoflagellates

Single-celled to colonial protists characterized by two flagella, one girdling the cell and the other trailing the cell. Some dinoflagellates exist in coral, in a symbiotic relationship. These dinoflagellates are termed the zooxanthellae. Other dinoflagellates occur in such high numbers that the water is colored red, a phenomenon known as a red tide.

Unicellular

Single-celled.

Filaments

Slender, thread-like stalks that make up the stamens of a flower; topped by the anthers.

Planaria

Small free-living flatworms (Phylum Platyhelminthes) with bilateral symmetry and cephalization. The freshwater type is often used as an experimental organism.

Vesicles

Small membrane-bound spaces in most plant and animal cells that transport macromolecules into and out of the cell and carry materials between organelles in the cell.

Ribosomes

Small organelles made of rRNA and protein in the cytoplasm of prokaryotic and eukaryotic cells; aid in the production of proteins on the rough endoplasmic reticulum and ribosome complexes. The site of protein synthesis. The ribosome is composed of two subunits that attach to the mRNA at the beginning of protein synthesis and detach when the polypeptide has been translated.

Bursae

Small sacs lined with synovial membrane and filled with synovial fluid; act as cushions to reduce friction between tendons and bones.

Bronchioles

Small tubes in the lungs that are formed by the branching of the bronchi; terminate in the alveoli.

Transfer RNAs (tRNAs)

Small, single-stranded RNA molecules that bind to amino acids and deliver them to the proper codon on messenger RNA. The trucks of protein synthesis that carry the specified amino acid to the ribosome. Abbreviated tRNA.

Capillaries

Small, thin-walled blood vessels that allow oxygen to diffuse from the blood into the cells and carbon dioxide to diffuse from the cells into the blood.

Companion Cells

Specialized cells in the phloem that load sugars into the sieve elements and help maintain a functional plasma membrane in the sieve elements.

Basidia

Specialized club-shaped structures on the underside of club fungi (Basidiomycetes) within which spores form (sing.: basidium).

Guard Cells

Specialized epidermal cells that flank stomates and whose opening and closing regulates gas exchange and water loss.

Schwann Cells

Specialized glial cells that form the myelin sheath that coats many axons. Cells surrounding the axons of some neurons, thus forming the myelin sheath.

Vascular System

Specialized tissues for transporting fluids and nutrients in plants; also plays a role in supporting the plant; one of the four main tissue systems in plants.

Biochemical Reactions

Specific chemical processes that occur in living things.

Genes

Specific segments of DNA that control cell structure and function; the functional units of inheritance. Sequences of DNA bases usually code for a polypeptide sequence of amino acids.

Nucleosomes

Spherical bodies formed by coils of chromatin. The nucleosomes in turn are coiled to form the fibers that make up the chromosomes.

Follicles (Thyroid)

Spherical structures that make up the thyroid gland; contain a gel-like colloid surrounded by a single layer of cells, which secrete thyroglobulin into the colloid.

Separation

Splitting of the cytoplasm by cytokinesis (= cytokinesis).

Microgametophyte

Stage of the plant life cycle that develops from or within a microspore. The microgametophyte produces sperm in specialized structures known as antheridia.

Stolons

Stems that grow along the surface of the ground; a method of plant vegetaive propagation.

Sensory Input

Stimuli that the nervous system receives from the external or internal environment; includes pressure, taste, sound, light, and blood pH.

Myofibrils

Striated contractile microfilaments in skeletal muscle cells.

Cell Wall

Structure produced by some cells outside their cell membrane; variously composed of chitin, peptidoglycan, or cellulose.

Seed

Structure produced by some plants in which the next generation sporophyte is surrounded by gametophyte nutritive tissues. An immature sporophyte in an arrested state of development, surrounded by a protective seed coat.

Pollen Tube

Structure produced by the tube nucleus in the pollen grain through which the sperm nucleus (or nuclei in angiosperms) proceed to travel through to reach the egg.

Root Cap

Structure that covers and protects the apical meristem in plant roots. Cells forming a protective series of layers over the root meristem.

Kinetochores

Structures at the centromeres of the chromosomes to which the fibers of the mitotic spindle connect.

Cristae

Structures formed by the folding of the inner membrane of a mitochondrion (sing.: crista).

Micelles

Structures formed when bile salts surround digested fats in order to enable the water-insoluble fats to be absorbed by the epithelial cells lining the small intestine.

Chromosomes

Structures in the nucleus of a eukaryotic cell that consist of DNA molecules that contain the genes.

Follicles (Ovary)

Structures in the ovary consisting of a developing egg surrounded by a layer of follicle cells.

Microsporangia

Structures of the sporophyte in which microspores are produced by meiosis. In flowering plants the microsporangia are known as anther sacs.

Antibiotics

Substances produced by some microorganisms, plants, and vertebrates that kill or inhibit the growth of bacteria.

Eccrine Glands

Sweat glands that are linked to the sympathetic nervous system and are widely distributed over the body surface.

Apocrine Glands

Sweat glands that are located primarily in the armpits and groin area; larger than the more widely distributed eccrine glands.

Tubers

Swollen underground stems in plants that store food, such as the irish potato.

Cytotoxic T cells

T cells that destroy body cells infected by viruses or bacteria; also attack bacteria, fungi, parasites, and cancer cells and will kill cells of transplanted organs if they are recognized as foreign; also known as killer T cells.

Birds

Taxonomic class of terrestrial vertebrates that are characterized by endothermy and feathers; descended from some group of reptiles (or possibly dinosaurs).

Reptiles

Taxonomic class of vertebrates characterized by scales and amniotic eggs; the first truly terrestrial vertebrate group.

Ray-Finned

Taxonomic group of fish, such as trout, tuna, salmon, and bass, that have thin, bony supports holding the fins away from the body and an internal swim bladder that changes the buoyancy of the body; one of the two main types of bony fishes.

Orders

Taxonomic subcategories of classes.

Classes

Taxonomic subcategories of phyla.

Genera

Taxonomic subcategories within families (sing.: genus), composed of one or more species.

X-Ray Diffraction

Technique utilized to study atomic structure of crystalline substances by noting the patterns produced by x-rays shot through the crystal.

Pseudopodia

Temporary cytoplasmic extensions from a cell that enables it to move (sing.: pseudopodium).

Adaptation

Tendency of an organism to suit its environment; one of the major points of Charles Darwin's theory of evolution by natural selection: organisms adapt to their environment. Those organisms best adapted will have a greater chance of surviving and passing their genes onto the next generation.

Antibiotic Resistance

Tendency of certain bacteria to develop a resistance to commonly overused antibiotics.

Taxon

Term applied group of organisms comprising a given taxonomic category

Blending

Term applied to 19th century belief that parental traits "blended" in their offspring; disproved by Mendel's work.

Sticky Ends

Term applied to DNA sequences cut with restriction enzymes where the cuts will bond with each other or with another sequence cut with the same enzyme.

RNA Transcript

Term applied to RNA transcribed in the nucleus.

Euglenoids

Term applied to a division of protozoans that have one long flagellum, no cell wall, and which may have chloroplasts.

Carnivores

Term applied to a heterotroph, usually an animal, that eats other animals. Carnivores function as secondary, tertiary, or top consumers in food chains and food webs.

Herbaceous

Term applied to a non-woody stem/plant with minimal secondary growth.

Radioisotope

Term applied to a radioactive isotope, such as carbon-14 or uranium 238. Radioisotope nuclei are unstable and spontaneously breakdown and emit one of a number of types of radiation.

Uninucleate

Term applied to cells having only a single nucleus.

Hardwoods

Term applied to dicot trees, as opposed to softwoods, a term applied to gymnosperms.

Dioecious

Term applied to plants having separate male and female plants.

Toxins

Term applied to poisons in living systems.

Ventral

Term applied to the lower side of a fish, or to the chest of a land vertebrate.

Selectively Permeable

Term describing a barrier that allows some chemicals to pass but not others. The cell membrane is such a barrier.

Herbivores

Term pertaining to a heterotroph, usually an animal, that eats plants or algae. Herbivores function in food chains and food webs as primary consumers.

Fauna

Term referring collectively to all animals in an area. The zoological counterpart of flora.

Presymptomatic Screening

Testing to detect genetic disorders that only become apparent later in life. The tests are done before the condition actually appears, such as with Huntington disease.

Prenatal Testing

Testing to detect the presence of a genetic disorder in an embryo or fetus; commonly done by amniocentesis or chorionic villi sampling.

Cerebellum

That part of the brain concerned with fine motor coordination and body movement, posture, and balance; is part of the hindbrain and is attached to the rear portion of the brain stem.

S Phase

That period of interphase when new DNA is synthesized as part of replication of the chromatin.

Exon

The DNA bases that code for an amino acid sequence. Exons are separated by introns that code for no amino acid sequences.

Photoperiodism

The ability of certain plants to sense the relative amounts of light and dark in a 24-hour period; controls the onset of flowering in many plants.

Energy

The ability to bring about changes or to do work.

Homeostasis

The ability to maintain a relatively constant internal environment.

Prehensile Movement

The ability to seize or grasp.

Body Fossil

The actual remains (however permineralized, compressed or otherwise post-mortem altered) of an organism; includes bones, shells, and teeth.

Life History

The age at sexual maturity, age at death, and age at other events in an individual's lifetime that influence reproductive traits.

Synapsis

The alignment of chromosomes during meiosis I so that each chromosome is beside its homologue.

Methionine

The amino acid coded for by the initiation codon; all polypeptides begin with methionine, although post-translational reactions may remove it.

Primary Meristems

The apical meristems on the shoot and root apices in plants that produce plant primary tissues.

Freshwater Biome

The aquatic biome consisting of water containing fewer salts than the waters in the marine biome; divided into two zones: running waters (rivers, streams) and standing waters (lakes, ponds).

Marine Biome

The aquatic biome consisting of waters containing 3.5% salt on average; includes the oceans and covers more than 70% of the Earth's surface; divided into benthic and pelagic zones.

Zone of Physiological Stress

The area in a population's geographic range where members of population are rare due to physical and biological limiting factors.

region of elongation

The area in the tip of a plant root where cells grow by elongating, thereby increasing the length of the root.

Region of Division

The area of cell division in the tip of a plant root.

Fovea

The area of the eye in which the cones are concentrated.

Nucleoid

The area of the prokaryotic cytoplasm where the chromatin is localized.

Zone of Intolerance

The area outside the geographic range where a population is absent; grades into the zone of physiological stress.

Region of Maturation (Differentiation)

The area where primary tissues and root hairs develop in the tip of a plant root.

Aorta

The artery that carries blood from the left ventricle for distribution throughout the tissues of the body. The largest diameter and thickest walled artery in the body.

Pulmonary Artery

The artery that carries blood from the right ventricle of the vertebrate heart to the lungs. Artery carrying oxygen-poor blood from the heart to the lungs.

Electrostatic Attraction

The attraction between atoms of opposite charge that holds the atoms together in ionic bonds.

Mutation Rate

The average occurrence of mutations in a species per a given unit of time.

Hair Bulb

The base of a hair; contains cells that divide mitotically to produce columns of hair cells.

Receptacle

The base that attaches a flower to the stem.

Keratinocytes

The basic cell type of the epidermis; produced by basal cells in the inner layer of the epidermis.

Taxis

The behavior when an animal turns and moves toward or away from an external stimulus (pl.: taxes).

Biliary System

The bile-producing system consisting of the liver, gallbladder, and associated ducts.

Niche

The biological role played by a species.

Inflammatory Response

The body's reaction to invading infectious microorganisms; includes an increase in blood flow to the affected area, the release of chemicals that draw white blood cells, an increased flow of plasma, and the arrival of monocytes to clean up the debris.

Complementary Nucleotides

The bonding preferences of nucleotides, Adenine with Thymine, and Cytosine with Guanine. Also referred to as complementary base pairing.

Appendicular Skeleton

The bones of the appendages (wings, legs, and arms or fins) and of the pelvic and pectoral girdles that join the appendages to the rest of the skeleton; one of the two components of the skeleton of vertebrates.

Tarsals

The bones that make up the ankle joint.

Carpals

The bones that make up the wrist joint.

Convergent Plate Boundary

The boundary between two plates that are moving toward one another.

Divergent Plate Boundary

The boundary between two tectonic plates that are moving apart.

Thalamus

The brain region that serves as a switching center for sensory signals passing from the brain stem to other brain regions; part of the diencephalon.

Cranium

The braincase; composed of several bones fitted together at immovable joints.

Cytology

The branch of biology dealing with cell structure.

Sternum

The breastbone.

Phylum

The broadest taxonomic category within kingdoms (pl.: phyla).

Opposable

The capability of being placed against the remaining digits of a hand or foot; e.g., the ability of the thumb to touch the tips of the fingers on that hand.

Primary Cell Wall

The cell wall outside the plasma membrane that surrounds plant cells; composed of the polysaccharide cellulose.

Melanocytes

The cells in the inner layer of the epidermis that produce melanin.

Phosphorylation

The chemical attachment of phosphorus to a molecule, usually associated with the storage of energy in the covalent bond that is also formed. Example: attachment of the third phosphate group to ADP in the formation of the higher energy form, ATP. Photophosphorylation is a type of phosphorylation associated with the formation of ATP in the photosynthesis process.

Thoracic Cavity

The chest cavity in which the heart and lungs are located.

Karyotype

The chromosomal characteristics of a cell; also, a representation of the chromosomes aligned in pairs.

Autosomes

The chromosomes other than the sex chromosomes. Each member of an autosome pair (in diploid organisms) is of similar length and in the genes it carries.

Sex Chromosomes

The chromosomes that determine the sex of an organism. In humans, females have two X chromosomes, and males have one X chromosome and one Y chromosome. Chromosome that determines the gender (sex) of the individual. Human males have a large X and a smaller Y sex chromosomes, while human females have two X sex chromosomes.

Systematics

The classification of organisms based on information from observations and experiments; includes the reconstruction of evolutionary relatedness among living organisms. Currently, a system that divides organisms into five kingdoms (Monera, Protista, Plantae, Fungi, Animalia) is widely used.

Basidiomycetes

The club fungi, a major group of fungi that all produce a structure (basidium) on which basidiospores are produced. Includes mushrooms and toadstools.

Start Codon

The codon (AUG) on a messenger RNA molecule where protein synthesis begins.

Macroevolution

The combination of events associated with the origin, diversification, extinction, and interactions of organisms which produced the species that currently inhabit the Earth. Large scale evolutionary change such as the evolution of new species (or even higher taxa) and extinction of species.

Ecosystem

The community living in an area and its physical environment.

Cephalization

The concentration of sensory tissues in the anterior part of the body (head).

Sex Linkage

The condition in which the inheritance of a sex chromosome is coupled with that of a given gene; e.g., red-green color blindness and hemophilia in humans. Traits located on the X-chromosome.

Linkage

The condition in which the inheritance of a specific chromosome is coupled with that of a given gene. The genes stay together during meiosis and end up in the same gamete.

Aridity

The condition of receiving sparse rainfall; associated with cooler climates because cool air can hold less water vapor than warm air. Many deserts occur in relatively warm climates, however, because of local or global influences that block rainfall.

Chemical Equilibrium

The condition when the forward and reverse reaction rates are equal and the concentrations of the products remain constant.

Pollen Grains

The containers for male gametophytes of seed plants produced in a microsporangium by meiosis. Microspores produced by seed plants that contain the male gametophyte.

Systole

The contraction of the ventricles that opens the semilunar valve and forces blood into the arteries.

Secondary Extinction

The death of one population due to the extinction of another, often a food species.

Latitudinal Diversity Gradient

The decrease in species richness that occurs as one moves away from the equator.

Entropy

The degree of disorder in a system. As energy is transferred from one form to another, some is lost as heat; as the energy decreases, the disorder in the system and thus the entropy increases.

Adaptive Radiation

The development of a variety of species from a single ancestral form; occurs when a new habitat becomes available to a population. Evolutionary pattern of divergence of a great many taxa from a common ancestral species as a result of novel adaptations or a recent mass extinction.

Parallel Evolution

The development of similar characteristics in organisms that are not closely related (not part of a monophyletic group) due to adaptation to similar environments and/or strategies of life.

Convergent Evolution

The development of similar structures in distantly related organisms as a result of adapting to similar environments and/or strategies of life. Example: wings of birds and insects, the body shape of dolphins, sharks, and the extinct marine reptiles known as ichthyosaurs.

Spermatogenesis

The development of sperm cells from spermatocytes to mature sperm, including meiosis.

Blastocyst

The developmental stage of the fertilized ovum by the time it is ready to implant; formed from the morula and consists of an inner cell mass, an internal cavity, and an outer layer of cells (the trophoblast).

Resting Potential

The difference in electrical charge across the plasma membrane of a neuron.

Founder Effect

The difference in gene pools between an original population and a new population founded by one or a few individuals randomly separated from the original population, as when an island population is founded by one or a few individuals; often accentuates genetic drift.

Diversity

The different types of organisms that occur in a community.

Sporophyte

The diploid stage of a plant exhibiting alternation of generations. The diploid, spore producing phase of the plant life cycle.

Divergent Evolution

The divergence of a single interbreeding population or species into two or more descendant species.

Resource Partitioning

The division of resources such that a few dominant species exploit most of the available resources while other species divide the remainder; helps explain why a few species are abundant in a community while others are represented by only a few individuals.

Mitosis

The division of the cell's nucleus and nuclear material of a cell; consists of four stages: prophase, metaphase, anaphase, and telophase. Cell xeroxing. Mitosis occurs only in eukaryotes. The DNA of the cell is replicated during interphase of the cell cycle and then segregated during the four phases of mitosis.

Cytokinesis

The division of the cytoplasm during cell division.

Peripheral Nervous System

The division of the nervous system that connects the central nervous system to other parts of the body. Components of the nervous system that transmit messages to the central nervous system.

Central Nervous System (CNS)

The division of the nervous system that includes the brain and spinal cord.

Stratification

The division of water in lakes and ponds into layers with different temperatures and oxygen content. Oxygen content declines with depth, while the uppermost layer is warmest in summer and coolest in winter.

Vas Deferens

The duct that carries sperm from the epididymis to the ejaculatory duct and urethra. The tube connecting the testes with the urethra.

Termination

The end of translation; occurs when the ribosome reaches the stop codon on the messenger RNA molecule and the polypeptide, the messenger RNA, and the transfer RNA molecule are released from the ribosome.

Second Law of Thermodynamics (Entropy)

The energy available after a chemical reaction is less than that at the beginning of a reaction; energy conversions are not 100% efficient.

Kilocalorie

The energy needed to heat 1000 grams of water from 14.5 to 15.5 degrees C.

Atmosphere

The envelope of gases that surrounds the Earth; consists largely of nitrogen (78%) and oxygen (21%).

Morphological Convergence

The evolution of basically dissimilar structures to serve a common function. For example: the wings of birds and insects.

Malpighian Tubules

The excretory organs of insects; a set of long tubules that open into the gut.

Niche Overlap

The extent to which two species require similar resources; specifies the strength of the competition between the two species.

Nondisjunction

The failure of chromosomes to separate properly during cell division. The unequal segregation of chromosomes during meiosis. This forms cells with either too many (possibly one or more single or sets of chromosomes too many) or too few chromosomes. Thought to be a common cause for Down Syndrome, where sufferers often have an extra copy of chromosome 21.

Ovum

The female gamete, egg.

Carpels

The female reproductive structures of a flower; consisting of the ovary, style, and stigma.

Diastole

The filling of the ventricle of the heart with blood.

Telophase

The final stage of mitosis in which the chromosomes migrate to opposite poles, a new nuclear envelope forms, and the chromosomes uncoil. The last phase of nuclear division in eukaryotes when the segregated chromosomes uncoil and begin to reform nuclei. This is immediately followed (in most cases) by cytokinesis.

Reductional Division

The first division in meiosis; results in each daughter cell receiving one member of each pair of chromosomes.

Pleistocene

The first geologic epoch of the Quaternary Period of the Cenozoic Era that ended 10,000 years ago with the retreat of the last glaciers.

Producers

The first level in a food pyramid; consist of organisms that generate the food used by all other organisms in the ecosystem; usually consist of plants making food by photosynthesis.

Penicillin

The first of the so-called wonder drugs; discovered by Sir Alexander Fleming.

Triassic Period

The first period of the Mesozoic Era between 225 and 185 million years ago. Pangaea began to break up during this time. The ancestors of dinosaurs were present, as were early mammals and mammal-like reptiles.

Primary Root

The first root formed by a plant.

Initiation

The first step in translation; occurs when a messenger RNA molecule, a ribosomal subunit, and a transfer RNA molecule carrying the first amino acid bind together to form a complex; begins at the start codon on mRNA.

Immunoglobulins

The five classes of protein to which antibodies belong (IgD, IgM, IgG, IgA, IgE).

Biochemical Cycle

The flow of an element through the living tissue and physical environment of an ecosystem; e.g., the carbon, hydrogen, oxygen, nitrogen, sulfur, and phosphorus cycles.

Matter Cycling

The flow of matter through various organisms and the physical environment of an ecosystem.

Blastocoel

The fluid-filled cavity at the center of a blastula.

Tertiary Structure

The folding of a protein's secondary structure into a functional three-dimensional configuration. Shape assumed by protein due to interactions between amino acids far apart on the chain.

DNA Hybridization

The formation of hybrid DNA molecules that contain a strand of DNA from two different species. The number of complementary sequences in common in the two strands is an indication of the degree of relatedness of the species.

Tetrad

The four chromatids in each cluster during synapsis; formed by the two sister chromatids in each of the two homologous chromosomes.

Period

The fundamental unit in the hierarchy of time units; a part of geologic time during which a particular sequence of rocks designated as a system was deposited. Units of geological time that are the major subdivisions of Eras.

Fertilization

The fusion of two gametes (sperm and ovum) to produce a zygote that develops into a new individual with a genetic heritage derived from both parents. Strictly speaking, fertilization can be divided into the fusion of the cells (plasmogamy) and the fusion of nuclei (karyogamy).

Reduction

The gain of an electron or a hydrogen atom. The gain of electrons or hydrogens in a chemical reaction.

Petiole

The generally non-leafy part of the leaf that attaches the leaf blade to the stem; celery and rhubarb are examples of a leaf petiole that we use as food. The stalk connecting the leaf blade to the stem.

Thermogenesis

The generation of heat by raising the body's metabolic rate; controlled by the hypothalamus.

Genotype

The genetic (allelic) makeup of an organism with regard to an observed trait.

Nucleotide Sequences

The genetic code encrypted in the sequence of bases along a nucleic acid.

Cretaceous Period

The geologic period between the Jurassic Period (140 million years ago) and the Tertiary Period (beginning 65 million years ago). The Cretaceous was marked by a mass extinction that closed the period along with the reign of the non avian dinosaurs.

Silurian Period

The geological time period of the Paleozoic Era following the Ordovician, between 435 and 395 million years ago, when plants colonized the land.

Chlorophyll A

The green photosynthetic pigment common to all photosynthetic organisms.

Monoculture

The growth of only one species in a given area; such as a cornfield or other agricultural field.

Gametophyte

The haploid stage of a plant exhibiting alternation of generations, generates gametes by the process of mitosis.

Greenhouse Effect

The heating that occurs when gases such as carbon dioxide trap heat escaping from the Earth and radiate it back to the surface; so-called because the gases are transparent to sunlight but not to heat and thus act like the glass in a greenhouse.

Consumers

The higher levels in a food pyramid; consist of primary consumers, which feed on the producers, and secondary consumers, which feed on the primary consumers.

Cardiovascular System

The human circulatory system consisting of the heart and the vessels that transport blood to and from the heart.

Uniformitarianism

The idea that geological processes have remained uniform over time and that slight changes over long periods can have large-scale consequences; proposed by James Hutton in 1795 and refined by Charles Lyell during the 1800s. The principle on which modern geology was founded: processes operating today on the earth operated in much the same way in the geologic past. Sometimes expressed as "the present is the key to the past".

Endocytosis

The incorporation of materials from outside the cell by the formation of vesicles in the plasma membrane. The vesicles surround the material so the cell can engulf it.

Depth Diversity Gradient

The increase in species richness with increasing water depth until about 2000 meters below the surface, where species richness begins to decline.

Pioneer Community

The initial community of colonizing species.

Spongy Bone

The inner layer of bone; found at the ends of long bones and is less dense than compact bone. Some spongy bone contains red marrow.

Endoderm

The inner layer of cells in embryonic development that gives rise to organs and tissues associated with digestion and respiration.

Wood

The inner layer of the stems of woody plants; composed of xylem.

Endometrium

The inner lining of the uterus.

Retina

The inner, light-sensitive layer of the eye; includes the rods and cones.

Gene Therapy

The insertion of normal or genetically altered genes into cells through the use of recombinant DNA technology; usually done to replace defective genes as part of the treatment of genetic disorders.

Endothermy

The internal control of body temperature; the ability to generate and maintain internal body heat.

Synapse

The junction between an axon and an adjacent neuron.

Nucleus (Cell)

The largest, most prominent organelle in eukaryotic cells; a round or oval body that is surrounded by the nuclear envelope and contains the genetic information necessary for control of cell structure and function.

Permian Period

The last geologic time period of the Paleozoic Era, noted for the greatest mass extinction in earth history, when nearly 96% of species died out.

Photic Zone

The layer of the ocean that is penetrated by sunlight; extends to a depth of about 200 meters.

Hydrophytic Leaves

The leaves of plants that grow in water or under conditions of abundant moisture.

Xerophytic Leaves

The leaves of plants that grow under arid conditions with low levels of soil and water. Usually characterized by water-conserving features such as thick cuticle and sunken stomatal pits.

Mesophytic Leaves

The leaves of plants that grow under moderately humid conditions with abundant soil and water.

Genetic Code

The linear series of nucleotides, read as triplets, that specifies the sequence of amino acids in proteins. Each triplet specifies an amino acid, and the same codons are used for the same amino acids in almost all life-forms, an indication of the universal nature of the code.

Plasma

The liquid portion of the blood. Along with the extracellular fluid, it makes up the internal environment of multicellular organisms.

occipital lobe

The lobe of the cerebral cortex located at the rear of the head; is responsible for receiving and processing visual information.

Frontal Lobe

The lobe of the cerebral cortex that is responsible for motor activity, speech, and thought processes.

Temporal Lobe

The lobe of the cerebral cortex that is responsible for processing auditory signals.

Parietal Lobe

The lobe of the cerebral cortex that lies at the top of the brain; processes information about touch, taste, pressure, pain, and heat and cold.

Systemic Circuit

The loop of the circulatory system that carries blood through the body and back to the heart.

Pulmonary Circuit

The loop of the circulatory system that carries blood to and from the lungs.

Deletion

The loss of a chromosome segment without altering the number of chromosomes.

Oxidation

The loss of electrons from the outer shell of an atom; often accompanied by the transfer of a proton and thus involves the loss of a hydrogen ion. The loss of electrons or hydrogens in a chemical reaction.

Transpiration

The loss of water molecules from the leaves of a plant; creates an osmotic gradient; producing tension that pulls water upward from the roots.

Gonads

The male and female sex organs.

Sperm

The male gamete.

Testes

The male gonad; produce spermatozoa and male sex hormones. Male gonads in mammals. Singular, testis. Paired organs that contain seminiferous tubules in which sperm are produced.

Stamens

The male reproductive structures of a flower; usually consist of slender, thread-like filaments topped by anthers. The male reproductive structures in the flower, composed of a filament and anther.

Epistasis

The masking of the effects of one gene by the action of another, example: widow's peak masked by the baldness gene.

Mycelium

The mass of interwoven filaments of hyphae in a fungus.

Stroma

The matrix surrounding the grana in the inner membrane of chloroplasts. The area between membranes (thylakoids, grana) inside the chloroplast.

Maximum Sustainable Yield (MSY)

The maximum number of a food or game population that can be harvested without harming the population's ability to grow back.

Carrying Capacity

The maximum population size that can be regularly sustained by an environment; the point where the population size levels off in the logistic growth model.

Ventilation

The mechanics of breathing in and out through the use of the diaphragm and muscles in the wall of the thoracic cavity.

Sodium-Potassium Pump

The mechanism that uses ATP energy to reset the sodium and potassium ions after transmission of a nerve impulse.

Binary Fission

The method by which bacteria reproduce. The circular DNA molecule is replicated; then the cell splits into two identical cells, each containing an exact copy of the original cell's DNA.

Mesoderm

The middle layer of cells in embryonic development; gives rise to muscles, bones, and structures associated with reproduction. The middle embryonic tissue layer. Cells and structures arising from the mesoderm include the bone, blood, muscle, skin, and reproductive organs.

Energy of Activation

The minimum amount of energy required for a given reaction to occur; varies from reaction to reaction.

Brain

The most anterior, most highly developed portion of the central nervous system.

Tropical Rainforest Biome

The most complex and diverse biome; found near the equator in South America and Africa; characterized by thin soils, heavy rainfall, and little fluctuation in temperature.

Societies

The most highly organized type of social organization; consist of individuals that show varying degrees of cooperation and communication with one another; often have a rigid division of labor.

Synovial Joint

The most movable type of joint. The bones are covered by connective tissue, the interior of which is filled with synovial fluid, and the ends of the bones are covered with cartilage.

Quaternary Period

The most recent geologic period of the Cenozoic Era, the Quaternary began 2 million years ago with the growth of northern hemisphere continental glaciers and the ice age.

Medusa

The motile bell-shaped form of body plan in cnidarians; e.g., jellyfish.

Energy Flow

The movement of energy through a community via feeding relationships.

Plate Tectonics

The movement of the plates that make up the surface of the Earth. The revolutionary paradigm in geology that the earth's crust is composed of rigid segments (plates) in constant (although considered slow in a human-scale time frame) motion (tectonics) relative to each other.

Hyphae

The multinucleate or multicellular filaments that make up the mycelium (body) of a fungus (sing.: hypha).

Stomach

The muscular organ between the esophagus and small intestine that stores, mixes, and digests food and controls the passage of food into the small intestine

Esophagus

The muscular tube extending between and connecting the pharynx to the stomach.

Pangaea

The name proposed by German meteorologist Alfred Wegener for a supercontinent that existed at the end of the Paleozoic Era and consisted of all the Earth's landmasses.

pH

The negative logarithm of the H+ ion concentration. The pH is a measure of the acidity or basic character of a solution. Since it measures a fraction, the larger the pH number, the less H ions are present in a solution.

Bryophytes

The nonvascular plants, characterized by life cycles dominated by the gametophyte phase. This group includes the mosses, liverworts, and hornworts, which lack lignified conducting tissues.

Laurasia

The northern part of the supercontinent of Pangaea, composed of the present-day North America, Europe, and Asia.

Species Diversity

The number of living species on Earth.

Atomic Number

The number of protons in the nucleus of an atom.

Species Richness

The number of species present in a community.

Phenotype

The observed properties or outward appearance of a trait. The physical expression of the alleles possessed by an organism.

Mouth

The oral cavity; the entrance to the digestive system where food is broken into pieces by the teeth and saliva begins the digestion process.

Uterus

The organ that houses and nourishes the developing embryo and fetus. The womb. Female reproductive organ in which the fertilized egg implants.

Compact Bone

The outer dense layer that forms the shaft of the long bones; made up of concentric layers of mineral deposits surrounding a central opening.

Labia Majora

The outer folds of skin that cover and protect the genital region in women.

Trophoblast

The outer layer of cells of a blastocyst that adhere to the endometrium during implantation.

Cerebral Cortex

The outer layer of gray matter in the cerebrum; consists mainly of neuronal cell bodies and dendrites in humans; associated with higher functions, including language and abstract thought.

Bark

The outer layer of the stems of woody plants; composed of an outer layer of dead cells (cork) and an inner layer of phloem.

Ectoderm

The outermost of the three germ layers, or masses of cells, which appears early in the development of an animal embryo.

Cerebrum

The part of the forebrain that includes the cerebral cortex; the largest part of the human brain.

Evaporation

The part of the hydrologic cycle in which liquid water is converted to vapor and enters the atmosphere.

Precipitation

The part of the hydrologic cycle in which the water vapor in the atmosphere falls to Earth as rain or snow.

Hydrosphere

The part of the physical environment that consists of all the liquid and solid water at or near the Earth's surface.

Pharynx

The passageway between the mouth and the esophagus and trachea. Food passes from the pharynx to the esophagus, and air passes from the pharynx to the trachea.

Systolic Pressure

The peak blood pressure when ventricles contract.

Interphase

The period between cell divisions when growth and replacement occur in preparation for the next division; consists of gap 1 (G1), synthesis (S), and gap 2 (G2).

Mesozoic Era

The period of geologic time beginning 245 million years ago and ending 65 million years ago; the age of the dinosaurs and cycads, the Mesozoic falls between the Paleozoic and Cenozoic Eras and includes the Triassic, Jurassic, and Cretaceous Periods.

Cenozoic Era

The period of geologic time beginning after the end of the Mesozoic Era 65 million years ago and encompassing the present. Commonly referred to as the age of mammals.

Archean/Proterozoic Era

The period of time beginning 4.6 billion years ago with the formation of the Earth and ending 570 million years ago.

Paleozoic Era

The period of time beginning 570 million years ago ending 245 million years ago; falls between the Proterozoic and Mesozoic Eras and is divided into the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian Periods.

Species Packing

The phenomenon in which present-day communities generally contain more species than earlier communities because organisms have evolved more adaptations over time.

Light Reactions

The photosynthetic process in which solar energy is harvested and transferred into the chemical bonds of ATP; can occur only in light.

Chlorophyll

The pigment in green plants that absorbs solar energy.

Shoot

The plant stem; provides support for the leaves and flowers; one of the three major plant organs; also referred to as the shoot system.

Neuromuscular Junction

The point where a motor neuron attaches to a muscle cell.

Hair Shaft

The portion of a hair that extends above the skin's surface.

Hair Root

The portion of a hair that extends from the skin's surface to the hair bulb.

Brain Stem

The portion of the brain that is continuous with the spinal cord and consists of the medulla oblongata and pons of the hindbrain and the midbrain.

Renal Tubule

The portion of the nephron where urine is produced.

Somatic Nervous System

The portion of the peripheral nervous system consisting of the motor neuron pathways that innervate skeletal muscles.

Sensory (Afferent) Pathways

The portion of the peripheral nervous system that carries information from the organs and tissues of the body to the central nervous system.

Motor (Efferent) Pathways

The portion of the peripheral nervous system that carries signals from the central nervous system to the muscles and glands.

Autonomic System

The portion of the peripheral nervous system that stimulates smooth muscle, cardiac muscle, and glands; consists of the parasympathetic and sympathetic systems.

Anus

The posterior opening of the digestive tract.

Acid Rain

The precipitation of sulfuric acid and other acids as rain. The acids form when sulfur dioxide and nitrogen oxides released during the combustion of fossil fuels combine with water and oxygen in the atmosphere.

Cortisol

The primary glucocorticoid hormone; released by the adrenal cortex.

Chemiosmosis

The process by which ATP is produced in the inner membrane of a mitochondrion. The electron transport system transfers protons from the inner compartment to the outer; as the protons flow back to the inner compartment, the energy of their movement is used to add phosphate to ADP, forming ATP.

Ossification

The process by which embryonic cartilage is replaced with bone.

Endochondral Ossification

The process by which human bones form from cartilage.

Photosynthesis

The process by which plant cells use solar energy to produce ATP. The conversion of unusable sunlight energy into usable chemical energy, associated with the actions of chlorophyll.

Absorption

The process by which the products of digestion are transferred into the body's internal environment, enabling them to reach the cells.

Artificial Selection

The process in which breeders choose the variants to be used to produce succeeding generations.

Metastasis

The process in which cancer cells break away from the original tumor mass and establish new tumor sites elsewhere in the body.

Tubular Secretion

The process in which ions and other waste products are transported into the distal tubules of the nephron.

Implantation

The process in which the blastocyst embeds in the endometrium.

Menstruation

The process in which the uterine endometrium breaks down and sheds cells, resulting in bleeding; occurs approximately once a month. The first day marks the beginning of the menstrual and ovarian cycles.

Digestion

The process of breaking down food into its molecular and chemical components so that these nutrient molecules can cross plasma membranes.

Metamorphosis

The process of changing from one form to another; e.g., in insects, from the larval stage to the pupal stage to the reproductive adult stage.

Integration

The process of combining incoming information; one of the functions of the nervous system.

Dendrochronology

The process of determining the age of a tree or wood used in structures by counting the number of annual growth rings.

Natural Selection

The process of differential survival and reproduction of fitter genotypes; can be stabilizing, directional, or disruptive. Better adapted individuals are more likely to survive to reproductive age and thus leave more offspring and make a larger contribution to the gene pool than do less fit individuals. The differential survival and reproductive successes of individuals in a variable population that powers the evolutionary process. When all individuals survive and reproduce (except for chance occurrences) natural selection works at a lower rate, if at all.

Vaccination

The process of protecting against infectious disease by introducing into the body a vaccine that stimulates a primary immune response and the production of memory cells against the disease-causing agent.

Excretion

The process of removing the waste products of cellular metabolism from the body.

Oogenesis

The production of ova. The development of a diploid cell into a haploid ovum or egg cell.

Dominance

The property of one of a pair of alleles that suppresses the expression of the other member of the pair in heterozygotes.

Capsid

The protein "shell" of a free virus particle.

Actin

The protein from which microfilaments are composed; forms the contractile filaments of sarcomeres in muscle cells.

Tubulins

The protein subunits from which microtubules are assembled.

Uracil

The pyrimidine that replaces thymine in RNA molecules and nucleotides.

Net Secondary Productivity (NSP)

The rate at which consumer and decomposer biomass is produced in a community.

Net Primary Productivity (NPP)

The rate at which producer (usually plants) biomass is created in a community.

Birth Rate

The ratio between births and individuals in a specified population at a particular time.

Death Rate

The ratio between deaths and individuals in a specified population at a particular time.

Phototropism

The reaction of plants to light in which the plants bend toward the light. Plant response to light by unequal growth caused by concentration of the plant hormone Indole Acetic Acid (IAA, an auxin) on the darker side of the plant shoot.

Menstrual Cycle

The recurring secretion of hormones and associated uterine tissue changes; typically 28 days in length.

Community Simplification

The reduction of overall species diversity in a community; generally caused by human activity.

Taiga Biome

The region of coniferous forest extending across much of northern Europe, Asia, and North America; characterized by long, cold winters and short, cool summers and by acidic, thin soils.

Medulla Oblongata

The region of the brain that, with the pons, makes up the hindbrain; controls heart rate, constriction and dilation of blood vessels, respiration, and digestion.

Pons

The region that, with the medulla oblongata, makes up the hindbrain, which controls heart rate, constriction and dilation of blood vessels, respiration, and digestion.

Thermoregulation

The regulation of body temperature.

Age Structure

The relative proportion of individuals in each age group in a population.

Secretion

The release of a substance in response to the presence of food or specific neural or hormonal stimulation.

Ovulation

The release of the oocyte onto the surface of the ovary; occurs at the midpoint of the ovarian cycle. The release of the ovum (egg) from the ovary after the peaking of luteinizing hormone concentration in the blood during the menstrual cycle.

Filtration

The removal of water and solutes from the blood; occurs in the glomerulus of the nephron.

Flowers

The reproductive structures in angiosperm sporophytes where gametophytes are generated.

Conditioned Response

The response to a stimulus that occurs when an animal has learned to associate the stimulus with a certain positive or negative effect.

Human Immunodeficiency Virus (HIV)

The retrovirus that attacks T-cells in the human immune system, destroying the body's defenses and allowing the development of AIDS. Huntington Disease: A progressive and fatal disorder of the nervous system that develops between the ages of 30 and 50 years; caused by an expansion of a trinucleotide repeat and inherited as a dominant trait.

Reabsorption

The return to the blood of most of the water, sodium, amino acids, and sugar that were removed during filtration; occurs mainly in the proximal tubule of the nephron.

Pyloric Sphincter

The ring of muscle at the junction of the stomach and small intestine that regulates the movement of food into the small intestine.

Ecological Niche

The role an organism occupies and the function it performs in an ecosystem; closely associated with feeding.

Jejunum

The second portion of the small intestine.

Distal Tubule

The section of the renal tubule where tubular secretion occurs.

Vertebrae

The segments of the spinal column; separated by disks made of connective tissue.

Selective Breeding

The selection of individuals with desirable traits for use in breeding. Over many generations, the practice leads to the development of strains with the desired characteristics.

Genetic Divergence

The separation of a population's gene pool from the gene pools of other populations due to mutation, genetic drift, and selection. Continued divergence can lead to speciation.

Primary Structure

The sequence of amino acids in a protein.

Cell Cycle

The sequence of events from one division of a cell to the next; consists of mitosis (or division) and interphase.

Community Succession

The sequential replacement of species in a community by immigration of new species and by local extinction of old ones.

Polyp

The sessile form of life history in cnidarians; e.g., the freshwater hydra.

Heterogametic Sex

The sex with two different chromosomes, such as males in humans and Drosophila.

Overkill

The shooting, trapping, or poisoning of certain populations, usually for sport or economic reasons.

Food Chain

The simplest representation of energy flow in a community. At the base is energy stored in plants, which are eaten by small organisms, which in turn are eaten by progressively larger organisms; the food chain is an oversimplification in that most animals do not eat only one type of organism.

Leaves

The site of photosynthesis; one of the three major organs in plants.

Antigenic Determinant

The site on an antigen to which an antibody binds, forming an antigen-antibody complex.

Chiasma

The site where the exchange of chromosome segments between homologous chromosomes takes place (crossing-over) (pl.: chiasmata).

Integumentary System

The skin and its derivatives (hair, nails, feathers, horns, antlers, and glands), which in multicellular animals protect against invading foreign microorganisms and prevent the loss or exchange of internal fluids.

Axial Skeleton

The skull, vertebral column, and rib cage; one of the two components of the skeleton in vertebrates.

Arterioles

The smallest arteries; usually branch into a capillary bed.

Atom

The smallest indivisible particle of matter that can have an independent existence.

Minimum Viable Population (MVP)

The smallest population size that can avoid extinction due to breeding problems or random environmental fluctuations.

Cells

The smallest structural units of living matter capable of functioning independently.

Venules

The smallest veins. Blood flows into them from the capillary beds. Small veins that connect a vein with capillaries.

Lithosphere

The solid outer layer of the Earth. Includes both the land area and the land beneath the oceans and other water bodies.

Morula

The solid-ball stage of the preimplantation embryo.

Synaptic Cleft

The space between the end of a neuron and an adjacent cell.

Pleural Cavity

The space between the sheets of pleura (one covering the inside of the thoracic cavity, the other covering the outside of the lungs).

Geological Time

The span of time that has passed since the formation of the Earth and its physical structures; also, a timescale that focuses on events on the order of thousands of years or more.

Thylakoids

The specialized membrane structures in which photosynthesis takes place. Internal membranes in the chloroplast where the light reaction chemicals are embedded. Collections of thylakoids form the grana.

Promoter

The specific nucleotide sequence in DNA that marks the beginning of a gene.

Radioactive Decay

The spontaneous decay of an atom to an atom of a different element by emission of a particle from its nucleus (alpha and beta decay) or by electron capture.

Diffusion

The spontaneous movement of particles from an area of higher concentration to an area of lower concentration.

Basidiospores

The spores formed on the basidia of club fungi (Basidiomycetes).

Climax Community

The stage in community succession where the community has become relatively stable through successful adjustment to its environment.

Metaphase

The stage of eukaryotic cell division (mitosis or meiosis) in which the chromosomes line up at the equator of the cell.

Node

The stem region of a plant where one or more leaves attach. Where leaves are attached to stems.

Internodes

The stem regions between nodes in plants.

Stomatal Apparatus

The stomata and guard cells that control the size of the stoma.

Negative Feedback

The stopping of the synthesis of an enzyme by the accumulation of the products of the enzyme-mediated reaction.

Template Strand

The strand of DNA that is transcribed to make RNA.

Secondary Structure

The structure of a protein created by the formation of hydrogen bonds between different amino acids; can be a pleated sheet, alpha helix, or random coil. Shape of a protein caused by attraction between R-groups of amino acids.

Umbilical Cord

The structure that connects the placenta and the embryo; contains the umbilical arteries and the umbilical vein.

Sporangia

The structures in which spores are produced (sing.: sporangium).

Paleontology

The study of ancient life by collection and analysis of fossils.

Ecology

The study of how organisms interact with each other and their physical environment.

Palynology

The study of palynomorphs and other acid-resistant microfossils usually produced by plants, protists, and fungi.

Biogeography

The study of the distribution of plants and animals across the Earth.

Sympathetic System

The subdivision of the autonomic nervous system that dominates in stressful or emergency situations and prepares the body for strenuous physical activity, e.g., causing the heart to beat faster.

Parasympathetic System

The subdivision of the autonomic nervous system that reverses the effects of the sympathetic nervous system. Part of the autonomic nervous system that controls heartbeat, respiration and other vital functions.

Eubacteria

The subunit of the Monera that includes the true bacteria such as E. coli. One of the three major groups of prokaryotes in the Kingdom Monera. The eubacteria have cell walls containing peptidoglycan.

Amino Acids

The subunits (monomers) from which proteins (polymers) are assembled. Each amino acid consists of an amino functional group, and a carboxylic acid group, and differs from other amino acids by the composition of an R group.

Nucleotides

The subunits of nucleic acids; composed of a phosphate, a sugar, and a nitrogen-containing base. The fundamental structural unit of the nucleic acid group of organic macromolecules. Some nucleotides are involved in information storage (as nucleotides in DNA), protein synthesis (as nucleotides in RNA), and energy transfers (as single nucleotide ATP, GTP, and double nucleotide NADH and NADPH).

Metabolism

The sum of all chemical reactions (energy exchanges) in cells.

Gene Pool

The sum of all the genetic information carried by members of a population. Note: there is no diving in the deep end of the gene pool!

Atomic Weight

The sum of the weights of an atom's protons and neutrons, the atomic weight differs between isotopes of the same element.

Fermentation

The synthesis of ATP in the absence of oxygen through glycolysis.

Transcription

The synthesis of RNA from a DNA template. The making of RNA from one strand of the DNA molecule.

Translation

The synthesis of protein on a template of messenger RNA; consists of three steps: initiation, elongation, and termination. Making of a polypeptide sequence by translating the genetic code of an mRNA molecule associated with a ribosome.

Protista

The taxonomic Kingdom from which the other three eukaryotic kingdoms (Fungi, Animalia and Plantae) are thought to have evolved. The earliest eukaryotes were single-celled organisms that would today be placed in this admittedly not monophyletic group. The endosymbiosis theory suggests that eukaryotes may have evolved independently several times.

Chlorophyta

The taxonomic division that contains what is commonly called the green algae.

Primates

The taxonomic order of mammals that includes prosimians (lemurs and tarsiers), monkeys, apes, and humans; characteristics include large brain, stereoscopic vision, and grasping hand.

Prey Switching

The tendency of predators to switch to a more readily available prey when one prey species becomes rare; allows the first prey population to rebound and helps prevent its extinction.

Half-Life

The time required for one-half of an original unstable radioactive element to be converted to a more stable daughter element.

Anther

The top of a stamen's filament; divided into pollen sacs in which the pollen grains form.

Geographic Range

The total area occupied by a population.

Biomass

The total weight of living tissue in a community.

Seed Coat

The tough outer layer of the seed, derived from the outer layers of the ovule.

Cellular Respiration

The transfer of energy from various molecules to produce ATP; occurs in the mitochondria of eukaryotes, the cytoplasm of prokaryotes. In the process, oxygen is consumed and carbon dioxide is generated.

Pollination

The transfer of pollen from the anthers to the stigma by a pollinating agent such as wind, insects, birds, bats, or in a few cases the opening of the flower itself.

Ecotones

The transition from one type of habitat or ecosystem to another, such as the transition from a forest to a grassland.

Vagina

The tubular organ that is the site of sperm deposition and also serves as the birth canal.

Chorion

The two-layered structure formed from the trophoblast after implantation; secretes human chorionic gonadotropin.

Complete Dominance

The type of inheritance in which both heterozygotes and dominant homozygotes have the same phenotype.

T Cells

The type of lymphocyte responsible for cell-mediated immunity; also protects against infection by parasites, fungi, and protozoans and can kill cancerous cells; circulate in the blood and become associated with lymph nodes and the spleen.

Cardiac Muscle

The type of muscle that is found in the walls of the heart. Cardiac muscle is striated but branched, unlike the straight-shaped striated skeletal muscle cells.

Euphotic Zone

The upper part of the marine biome where light penetrates and photosynthesis occurs; usually extends to about 200 meters below the water surface.

Duodenum

The upper part of the small intestine.

Atrioventricular (AV) Valve

The valve between each auricle and ventricle of the heart.

Pulmonary Vein

The vein that carries oxygenated blood from the lungs to the left atrium of the heart. Veins carrying oxygenated blood from the lungs to the heart.

Cytoplasm

The viscous semi fluid inside the plasma membrane of a cell; contains various macromolecules and organelles in solution and suspension.

Proximal Tubule

The winding section of the renal tubule where most reabsorption of water, sodium, amino acids, and sugar takes place.

Endosymbiosis

Theory that attempts to explain the origin of the DNA-containing mitochondria and chloroplasts in early eukaryotes by the engulfing of various types of bacteria that were not digested but became permanent additions to the ancestral "eukaryote".

Arteries

Thick-walled vessels that carry blood away from the heart. Singular=artery.

Veins

Thin-walled vessels that carry blood to the heart. Units of the circulatory system that carry blood to the heart.

Primary Body

Those parts of a plant produced by the shoot and root apical meristems.

Initiation Codon (AUG)

Three-base sequence on the messenger RNA that codes for the amino acid methionine; the start command for protein synthesis.

Corpus Callosum

Tightly bundled nerve fibers that connect the right and left hemispheres of the cerebrum.

Alveoli

Tiny, thin-walled, inflatable sacs in the lungs where oxygen and carbon dioxide are exchanged.

Phloem

Tissue in the vascular system of plants that moves dissolved sugars and other products of photosynthesis from the leaves to other regions of the plant. Phloem tissue consists of cells called sieve tubes and companion cells. Cells of the vascular system in plants that transport food from leaves to other areas of the plant.

Xylem

Tissue in the vascular system of plants that moves water and dissolved nutrients from the roots to the leaves; composed of various cell types including tracheids and vessel elements. Plant tissue type that conducts water and nutrients from the roots to the leaves.

Minerals

Trace elements required for normal metabolism, as components of cells and tissues, and in nerve conduction and muscle contraction.

Active Transport

Transport of molecules against a concentration gradient (from regions of low concentration to regions of high concentration) with the aid of proteins in the cell membrane and energy from ATP.

Channels

Transport proteins that act as gates to control the movement of sodium and potassium ions across the plasma membrane of a nerve cell.

Oviducts

Tubes that connect the ovaries and the uterus; transport sperm to the ova, transport the fertilized ova to the uterus, and serve as the site of fertilization; also called the fallopian tubes or uterine tubes.

Sieve Elements

Tubular, thin-walled cells that form a system of tubes extending from the roots to the leaves in the phloem of plants; lose their nuclei and organelles at maturity, but retain a functional plasma membrane.

Ribosomal Subunits

Two units that combine with mRNA to form the ribosomal-mRNA complex at which protein synthesis occurs.

Prokaryote

Type of cell that lacks a membrane-bound nucleus and has no membrane organelles; a bacterium. Prokaryotes are more primitive than eukaryotes. Cells lacking membrane-bound organelles and having a single circular chromosome, and ribosomes surrounded by a cell membrane. Prokaryotes were the first forms of life on earth, evolving over 3.5 billion years ago.

Cast

Type of fossil preservation where the original material of the fossil has decayed and been replaced later by another material, much the way a plaster cast is made in a mold.

Mold

Type of fossil preservation where the original material of the fossil has decayed but has left an impression in the surrounding sediments. Molds are often filled with a different material, producing strikingly beautiful fossils.

Compression

Type of fossilization in which the fossil is flattened (compressed)m by the weight of overlying sediment.

Relative Time

Type of geologic time (absolute time being the other) that places events in a sequence relative to each other.

B Cells

Type of lymphocyte responsible for antibody-mediated immunity; mature in the bone marrow and circulate in the circulatory and lymph systems where they transform into antibody-producing plasma cells when exposed to antigens.

Alpha Decay

Type of radioactive decay in which a radioisotope emits a large but slow-moving particle consisting of two protons and two neutrons.

Beta Decay

Type of radioactive decay in which a radioisotope emits a small, negatively-charged and fast-moving particle from its nucleus. The beta particle is similar in size, charge, and speed to an electron and is formed when a neutron in the radioisotope's nucleus converts to a proton.

Leaf Veins

Vascular tissue in leaves, arranged in a net-like network (reticulate venation) in dicots, and running parallel (parallel venation) to each other in monocots.

Retroviruses

Viruses that contain a single strand of RNA as their genetic material and reproduce by copying the RNA into a complementary DNA strand using the enzyme reverse transcriptase. The single-stranded DNA is then copied, and the resulting double-stranded DNA is inserted into a chromosome of the host cell.

Intracellular Parasites

Viruses that enter a host cell and take over the host's cellular machinery to produce new viral particles.

Leukocytes

White blood cells; primarily engaged in fighting infection.

Fluid-Mosaic

Widely accepted model of the plasma membrane in which proteins (the mosaic) are embedded in lipids (the fluid).

Secondary Xylem

Xylem produced by the vascular cambium in a woody plant stem or root; wood.