CIE A-LEVEL BIOLOGY DEFINITIONS

Gene

a length of DNA that codes for a particular polypeptide

Polymer

a molecule made up of many repeating subunits that are similar or identical to each other

Polysaccharide

a polymer whose subunits are monosaccharides joined together by a glycosidic bond (they are not sugars)

Macromolecule

a large biological molecule (in living organisms there are polysaccharides, polypeptides and polynucleotides)

Haploid cell

A cell containing only one set of chromosomes (n).

Diploid cell

A cell containing two sets of chromosomes (2n), one set inherited from each parent.

Dominant allele

An allele whose characteristic always shows up in the organism when the allele is present.

Allele

An alternative form of a gene found at the same locus

Codominant alleles

Both have an effect on the phenotype of a heterozygous organism

Endocytosis

Bulk movement of liquids or solids into a cell by the infolding of the cell surface membrane to form vesicles containing the substance; endocytosis is an active process requiring ATP

Recombinant DNA

DNA made by joining pieces of DNA from two or more different sources

homozygous

Having two identical alleles for a particular gene.

Recessive allele

One that is only expressed when no dominant allele is present

Genotype

The alleles possessed by an organism

phenotype

The characteristics of an organism; often resulting from an interaction between its genotype and environment

Gene mutation

a change in the base sequence in part of the DNA molecule. It may result in an altered polypeptide.

Organic molecule

a compound containing carbon and hydrogen

Infectious disease

a disease caused by pathogens

Non-infectious disease

a disease not caused by pathogens; includes genetic diseases, deficiency diseases and mental diseases

Antibody

a glycoprotein made by plasma cells derived from B-lymphocytes, secreted in response to an antigen; the variable region of the antibody is complementary in shape to its specific antigen

species

a group of organisms with similar morphology and physiology which can breed together to produce fertile offspring and are reproductively isolated from other species

Negative feedback

a process in which a change in some parameter brings about processes which move its level back towards normal again

ecosystem

a relatively self-contained, interacting community of organisms, and the environment in which they live and with which they interact

Monomer

a relatively simple molecule used as a basic building block for the synthesis of a polymer

Antigen

a substance that is foreign to the body and stimulates an immune response

Disaccharide

a sugar molecule formed by two monosaccharides joining together by a glycosidic bond

Disease

an illness or disorder of the body or mind that leads to poor health; each disease is associated with a set of signs and symptoms

structural genes

code for the proteins required by a cell for its structure or metabolism

regulatory genes

control the expression of other genes

Vaccination

giving a vaccine containing antigens for a disease, either by injection or by mouth; vaccination confers artificial active immunity

heterozygous

having two different alleles for a particular gene

Limiting factor

if a process is affected by more than one factor, the rate will be limited by the factor which is nearest its lowest value

Artificial immunity

immunity gained either by vaccination (active) or by injecting antibodies (passive)

Homeostasis

maintaining a relatively constant internal environment for the cells within the body, despite changes in the external environment

Osmosis

net movement of water molecules from a region of higher water potential to a region of lower water potential, through a partially permeable membrane (as a result of their random motion)

Homologous chromosomes

pair of chromosomes in a diploid cell that have the same structure as each other, with the same genes at the same loci, and that pair together to form a bivalent during the first division of meiosis

respiratory quotient

ratio of the volume of carbon dioxide given out in respiration to that of oxygen used

Non-self

refers to a substance or cell that is recognised by the system as being foreign and will stimulate an immune response

Self

refers to substances produced by the body that the immune system does not recognise as foreign, so they do not stimulate an immune response

Monosaccharide

single-sugar molecules with general formula (CH2O)n

Quaternary structure

the 3D arrangement of two or more polypeptides, or of a polypeptide and non-protein component

Resolution

the ability to distinguish between two points which are very close together (the higher the image resolution, the greater the detail which can be seen)

Exocytosis

the bulk movement of liquids or solids out of a cell, by the fusion of vesicles containing the substance with the cell surface membrane; exocytosis is an active process requiring ATP

Bioinformatics

the collection, processing and analysis of biological information and data using computer software

Tertiary structure

the compact structure of a polypeptide resulting from the 3D coiling of the already-folded chain of amino acids

Immune Response

the complex series of responses of the body to the entry of a foreign antigen; it involves the activity of lymphocytes and phagocytes

Facilitated diffusion

the diffusion of a substance through transport proteins in a cell membrane; the proteins provide hydrophilic areas that allow the molecules or ions to pass through the membrane which would otherwise be less permeable to them

Natural immunity

the immunity gained by being infected (active) or by receiving antibodies from the mother across the placenta or in colostrum (natural)

Active immunity

the immunity gained when an antigen enters the body, an immune response occurs and antibodies are produced by plasma cells

Passive immuntiy

the immunity gained without an immune response; antibodies are injected (artificial) or by receiving antibodies from the mother across the placenta or in colostrum (passive)

Transpiration

the loss of water vapour from a plant to its environment, by diffusion down a water potential gradient (most transpiration takes place through the stomata in the leaves)

Active transport

the movement of molecules or ions through transport proteins across a cell membrane against their concentration gradient using energy from ATP

Diffusion

the net movement of molecules or ions from a region of higher concentration to a region of lower concentration down a gradient (as a result of random movement of particles)

Magnification

the number of times greater that the image is than the actual object

F1 generation

the offspring resulting from a cross between an organism with a homozygous dominant genotype and one with a homozygous recessive genotype

F2 generation

the offspring resulting from a cross between two F1 organisms.

Locus

the position at which a particular gene is found on a particular chromosome; (the same gene is always found at the same locus)

Niche

the role of an organism in an ecosystem

Primary structure

the sequence of amino acids in a polypeptide (amino acids are held together by peptide bonds)

Secondary structure

the structure of a polypeptide resulting from the regular coiling or folding of the chain of amino acids eg. a-helix and B-pleated sheet

RQ = (formula)

volume of CO2 given out in unit time/ volume of O2 taken in in unit time (moles of CO2 given out/ moles of O2 taken in)