booster bio

What statement is true about antibiotic resistance of bacteria? A. It can be passed on to other bacteria through transfection B. Antibiotic resistance genes are mainly associated with R-plasmids C. A bacteria cannot be resistant against a specific antibiotic unless having encountered it before D. Gene transfer by transformation is not a valid way for bacteria to acquire resistance genes E. The only form of antibiotic resistance is decreased membrane permeability

Antibiotic resistance genes are mainly associated with R-plasmids R-plasmids tend to contain genes pertaining to anti-biotic resistance, which can get passed on to bacteria through conjugation or transformation. In fact, they tend to also contain resistance transfer genes which aid in the formation of a sex pilus between bacteria, as means of conjugation, as shown in the image below. Similar to any plasmid, they are double-stranded circular DNA and replicate separately from the bacterial chromosome.

The process of photosynthesis can be summarized as follows: 6CO2 + 6H2O → C6H12O6 + 6O2 Which process is ultimately responsible for the production of oxygen?

splitting of H2O The light-dependent reactions in the chloroplast of plants involve a light-driven electron transport chain. As electrons flow through the photosystems, they must be replenished at the start of the chain. Water is the source of these electrons. As the electron is lost from Chlorophyll P680 in photosystem II due to energy from incident photons, water is split into H+ ions, O2, and electrons which enter the electron transport chain of the light-dependent reactions. In the absence of water, there is no continued source of electrons and the light-dependent reactions cannot proceed.

What is the Hayflick limit associated with?

telomeres shorterning The Hayflick limit pertains to the limited number of times a cell can undergo division until it has to stop and undergo apoptosis. This arises from the concept of telomere shortening, which is the shortening of DNA with each round of replication. This is due to the way that the lagging strand works in which DNA polymerase needs an RNA primer to start replicating, and an RNA primer needs a DNA strand to connect, always leaving an un-replicated region at the end of the strand.

Where does the electron transport chain take place in chloroplast?

thylakoid membrane As far as functionality, understand that the light-dependent reactions and the associated electron transport chain occur on the thylakoid membrane. Protons are actively pumped inwards from the stroma into the thylakoid lumen via proteins on the thylakoid membrane

The pancreas releases enzymes used in digestion. Which of the following pancreatic enzymes is used to cleave peptide chains? A. Trypsin B. Nuclease C. Amylase D. Pepsin E. Maltose

Trypsin A protease is an enzyme that cleaves the peptide bonds within proteins. Out of all of the options provided, only trypsin and pepsin are proteases. However, between both of these enzymes, pepsin is an enzyme that is secreted by the stomach's digestive juices and not the pancreas, and thus it is not the correct answer. In contrast, trypsin is secreted by the pancreas in the form of a zymogen known as trypsinogen. Therefore, the answer is trypsin.

The broad use of antibiotics can result in

Vitamin A deficiency A broad-spectrum antibiotic is an antibiotic that acts on the two major bacterial groups, gram-positive and gram-negative, or any antibiotic that acts against a wide range of disease-causing bacteria. They are used when a bacterial infection is suspected but the group of bacteria is unknown or when infection with multiple groups of bacteria is suspected. This is in contrast to a narrow-spectrum antibiotic, which is effective against only a specific group of bacteria. Although powerful, broad-spectrum antibiotics pose specific risks, particularly the disruption of native, normal bacteria and the development of antimicrobial resistance. The destruction of the body's normal bacterial flora can disrupt the immunity, nutrition, and lead to a relative overgrowth in some bacteria or fungi. Broad-spectrum antibiotics, such as cephalosporins, are also known to reduce the absorption of vitamin K in the body. This can lead to the risk of bleeding if you take antibiotics for a long time. The image below shows how antibiotic resistance happens.

Which of the following structure of a bird embryo is used to store uric acid and is later used for gas exchange? A. Chorion B. Yolk Sac C. Amnion D. Placenta E. Allantois

Allantois The allantois is a component of the developing embryo's structure. It is a sac derived from the archenteron, the embryonic alimentary canal, as shown in the image below. The allantois serves as material storage or transport role. In the egg-laying birds and reptiles, the allantois stores uric acid waste but eventually fuses with the chorion for gas exchange roles. Therefore, Option E. Allantois, is the correct answer. In the placental mammals, the allantois forms the umbilical cord for material transport between embryo and mother. Note: Not all mammals are placental. The egg-laying mammals as also known as monotremes and include the platypus. The monotremes have extraembryonic membranes much like birds and reptiles. The marsupials have embryos that develop in an external pouch they do have a placenta but it is different in their formation than the other placental mammals.

A point mutation in the shell of a turtle results from a nucleotide change due to radiation. Which of the following best describes the likelihood of the turtle's progeny inheriting the mutation?

0% Sexual reproduction is the main form of reproduction in multicellular eukaryotes including animals, plants, and fungi. This form of reproduction involves the fusion of male and female gametes that combine into a diploid cell. Gametogenesis can only occur in the germ cells (also referred to as gametocytes) found in the gonads or reproductive organs. In a multicellular organism, every cell other than germ cells are known as somatic cells. Outside of the germ cells in the testes and ovaries, every other cell in the mammal is a somatic cell including the cells in a turtle's shell. Therefore, Option A. 0% is the correct answer as it would not be inherited.

In which order did the following appear during the origins of life? 1. Heterotrophic prokaryotes 2. Autotrophic prokaryotes 3. Eukaryotes 4. Ozone layer

1, 2,4,3 Early life began with the production of various gases, a few including CH4, NH3, CO2, H2, and N2. Complex molecules formed with energy from lightning, including amino acids and acetic acid. Following this, polymers began to form, including proteinoids which are abiotically produced polypeptides. Next to form were precursors to cells called protobionts. Primitive heterotrophic prokaryotes then formed which obtain energy by consuming other organic substances. From these formed primitive autotrophic prokaryotes which produce their own food from photosynthesis. O2 is formed during photosynthesis, and this reacted with UV light to form the ozone layer. By blocking UV light, at this point, abiotic synthesis of organic molecules would have terminated. Finally, according to the endosymbiotic theory, eukaryotes evolved from prokaryotes, with organelles such as chloroplasts and mitochondria originating from prokaryotic cells in symbiotic relationships.

Which of the following is true regarding the modern cell theory? A. All cells derive from pre-existing cells created using genetic information stored in the nucleus B. All cells have the same basic chemical composition C. All cells require water for survival D. All living things are composed of only cells E. Multicellular organisms are composed of unicellular organisms

All cells have the same basic chemical composition The Modern Cell Theory states: 1. All living organisms are composed of one or more cells 2. Cells arise from pre-existing living cells 3. Cells are the fundamental structure and function of living organism 4. All cells have the same basic chemical composition 5. Energy flow occurs within cells, via metabolism 6. Cells carry hereditary information

In response to low blood glucose levels, A. Insulin is released from beta cells of the pancreas B. Glucagon is released from beta cells of the pancreas C. Glucocorticoids are released from the adrenal medulla D. ACTH is released by the anterior pituitary E. ACTH is released by the posterior pituitary

ACTH is released by the anterior pituitary There are multiple responses by the body to low blood glucose levels to maintain homeostasis. In response to low blood glucose levels, alpha cells of the pancreas in the islets of Langerhans secrete glucagon into the bloodstream. This increases blood glucose concentration by stimulating the breakdown of liver glycogen stores (glycogenolysis) and forming glucose from lactic acid and certain amino acids (gluconeogenesis). In addition, the hypothalamus secretes CRH (corticotropin-releasing hormone) into the anterior pituitary, causing it to produce and secrete ACTH (adrenocorticotropic hormone) into the bloodstream. ACTH acts to increase the production of glucocorticoids such as cortisol by the adrenal cortex, stimulating gluconeogenesis. Furthermore, the hypothalamus also secretes GHRH (growth hormone-releasing hormone) into the anterior pituitary, which causes it to secrete hGH (human growth hormone) into the bloodstream. hGH increases the production of IGFs (insulin-like growth factors) and stimulates glycogenolysis. These systems are regulated by negative feedback systems, which are inhibited once the individual is no longer hypoglycemic. The image below provides a visualization to further help understand these concepts:

Which of the following prevents acetylcholine from remaining for too long in the synapse? A. Choline acetyltransferase B. Passive diffusion into pre-synaptic cell C. Acetylcholinesterase D. Degradation by post-synaptic cell surface receptors E. Uptake by post-synaptic cell

Acetylcholinesterase Acetylcholine is a neurotransmitter of the neuromuscular junction, between neurons in the sympathetic and parasympathetic nervous system, and the final product released by the last neuron on the target tissue. Acetylcholine receptors are known as cholinergic receptors and include G protein and channel types. Degradation of the acetylcholine signal in the synaptic cleft may occur in various mechanisms: Hydrolysis by acetylcholinesterase Diffusion away from the synaptic left Active reuptake by the pre-synaptic cell

What process immediately follows the penetration of the corona radiata by sperm? A. Inactivation of ZP3 protein B. Acrosomal reaction C. Cortical reaction D. Completion of meiosis II E. Capacitation

Acrosomal reaction After a sperm penetrates an egg's outer corona radiata layer, the sperm binds to the ZP3 protein of the zona pellucida to enable mutual recognition of species-compatible gametes. This binding to the ZP3 protein enables the acrosomal reaction to occur and initiates the start of fertilization. The release of acrosomal digestive enzymes allows the sperm to further penetrate the zona pellucida to fuse with the egg's plasma membrane to deposit its nucleus into the egg. At the same time the sperm binds to ZP3, the fast block of polyspermy occurs to trigger an influx of Na+ that prevents additional sperm from binding to ZP3. Therefore, Option B. Acrosomal reaction, is the correct answer.

Which of the following best describes the actions of ADH? A. Acts on collecting duct by increasing permeability to water B. Acts on distal convoluted tubule by increasing excretion of sodium C. Acts on collecting duct by decreasing permeability to water D. Acts on Loop of Henle to increase water reabsorption E. Acts on proximal convoluted tubule by decreasing permeability to water

Acts on collecting duct by increasing permeability to water ADH, or antidiuretic hormone, is a hormone that controls the amount of water in the body. It is produced by the hypothalamus of the brain and is then stored and secreted from the posterior pituitary. It is released in response to dehydration (high blood osmotic pressure). The kidney is made up of many nephrons, as seen in the image below, which filters blood and produces a filtrate that goes through collecting ducts to be excreted as urine. ADH acts here to increase the number of aquaporin channels which allow more water to be reabsorbed by the cells of the collecting duct and makes the urine more concentrated.

In which of the following groups of organisms can simultaneous transcription and translation be observed? A. Fungi B. Eukaryota C. Protista D. Protozoa E. Archaebacteria

Archaebacteria The key to understanding this question is identifying that only Option E is prokaryotic. In fact, prokaryotes lack any membrane-bound organelles. They do, however, have an area of densely packed genetic material known as the nucleoid or "nucleus-like" structure. The key to answering this question is that prokaryotes include eubacteria and archaea. Since prokaryotes lack a nuclear membrane that would separate the genetic material from the rest of the cytoplasm, simultaneous transcription and translation may occur as shown in the image below. As soon as RNA polymerase produces an mRNA from the DNA during transcription, ribosomes can immediately access this mRNA for translation into proteins. Therefore, Option E. Archaebacteria, which includes the only prokaryote kingdom, is the correct answer.

Microaerophiles

Are microorganisms that requires oxygen to survive, but requires environments containing lower levels of oxygen than that are present in the atmosphere

A marine biologist discovers an organism in the ocean with the following characteristics: bilateral symmetry, body segmentation, and multiple pairs of jointed appendages. Which of the following animal phyla would this organism best be categorized as? A. Chordata B. Annelida C. Echinodermata D. Platyhelminthes E. Arthropoda

Arthropoda Arthropoda is an animal phylum that includes spiders, insects, and crustaceans. A key characteristic that differentiates Arthropoda from other animal phyla is that they possess multiple pairs of jointed appendages. Other characteristics of Arthropoda are bilateral symmetry, well-developed nervous systems, and specialized body segments, or body segmentation. Considering the marine biologist discovered this organism in the ocean, we can assume it is of the class Crustacea, a subphylum of Arthropoda. Below are images of crustaceans. Note the multiple pairs of appendages that are characteristic of Arthropoda.

A botanist has discovered a new plant and notes that it is predominantly found in its gametophyte form. Which category does this plant most likely belong to? A. Bryophyte B. Angiosperm C. Gymnosperm D. Seedless Tracheophyte E. Endosperm

Bryophyte All land plants undergo reproduction with an alternation of generations scheme (shown below) which alternates between sexual and asexual reproduction stages. However, they differ in their most prominent phase. While the tracheophytes (including seedless tracheophytes, and seeded angiosperms and gymnosperms) are found most prominently in the diploid sporophyte phase, bryophytes are found most prominently in their gametophyte phase. Therefore, Option A. Bryophyte, is the correct answer. This dominance of the gametophyte phase and the lack of true vasculature characterizes the bryophytes.

Which of the following produces a hormone responsible for decreasing blood calcium levels? A. C Cells B. Adrenal cortex C. Adrenal medulla D. Posterior pituitary E. Anterior pituitary

C Cells Question #12 Which of the following produces a hormone responsible for decreasing blood calcium levels? A. C Cells [46%] B. Adrenal cortex [12%] C. Adrenal medulla [11%] D. Posterior pituitary [13%] E. Anterior pituitary [18%] Incorrect The correct answer is: A. 46% Answered Correctly 0 min, 41 secs Time Spent Structure & Function of Systems Question Category Concept Two glands in the endocrine system are responsible for controlling blood calcium levels: the thyroid gland and the parathyroid gland. C-cells (also known as parafollicular cells) of the thyroid gland produces the hormone calcitonin which acts to decrease the calcium levels in the blood. The Parathyroid Hormone (PTH) has the opposite effect as Calcitonin and is produced by the chief cells of the parathyroid gland.

What is true of B lymphocytes and their role in immunity? A. A component of the innate immune system B. A component of cell-mediated immunity C. Consists of cytotoxic B cells and Helper B cells D. Surrounds pathogens to tag for phagocytosis E. Can retain the memory of previously encountered antigens

Can retain the memory of previously encountered antigens The immune system consists of an innate and adaptive component. The adaptive immune system develops a specific response to a specific antigen. Though it does not play a major role in protecting the body during a primary immune response, it does protect the body to future infections in a secondary immune response. The B lymphocytes are a part of the adaptive immune system and control antibody-mediated or humoral immunity, as shown in the image below. They consist of plasma and memory B cells. The plasma cells play a role in producing antibodies. These antibodies may tag a pathogen for digestion via opsonization, neutralize said antigen, or lead to the activation of the complement system. The memory B cells retain information for receptors of antigens. This is essential in providing a significantly faster antibody response to subsequent infections by the same detected antigen in a secondary immune response. Under the clonal selection theory, a wide variety of antigens are present on pre-existing B cells even before the body has needed to respond to some pathogen. This wide variety of B cell receptors allows the body to potentially recognize a pathogenic antigen. When this occurs, this particular B cell will then undergo clonal expansion to multiply and produce memory B cells and plasma cells in preparation for a future infection by that same pathogen.

Polymerization of a macromolecule is correctly described by the formation of which of the following? A. Phospholipid bilayer from monosaccharides B. Cellular enzyme from amino acids C. Glycogen from nucleic acids D. Peptide from fatty acids E. RNA from cholesterols

Cellular enzyme from amino acids Polymers are macromolecules that are composed of many repeating subunits known as monomers. These polymers are made by dehydration synthesis. Note, however, that while all polymers are made of monomers, not all molecules with monomers are polymers. Phospholipids are one such example. Phospholipids consist of monomers including two fatty acids, glycerol, and a phosphate group. However, these are not repeating units so phospholipid is not a polymer. Sucrose is another example because it consists of only two monosaccharides rather than an extensive repeating chain like cellulose or glycogen.

Which of the following has the least direct effect on the SA node of the heart? A. Autonomic nervous system B. Peripheral nervous system C. Sympathetic nervous system D. Parasympathetic nervous system E. Central nervous system

Central nervous system 1. Central nervous system (i.e. brain and spinal cord) which has all of the information in the body and its surroundings. It relays this information to the peripheral nervous system. 2. Peripheral nervous system which contains the sensory and motor nerves. Within the motor nerves, we have the somatic and autonomic branches, where the somatic controls the voluntary contractions while autonomic controls the involuntary contractions. Involuntary contractions are found in the heart's pacemaker that is known as the SA node, where it is known to be innervated by two branches of the autonomic nervous system: a) Sympathetic branch → increases heart rate b) Parasympathetic branch → decreases heart rate

A patient with colon cancer undergoes a surgical procedure to have a lymph node examined. The purpose of this examination is to: A. Check the immune response B. Test for lymphomas C. Directly sample interstitial fluid D. Check where cancer cells have travelled E. Sample cancerous DNA

Check where cancer cells have travelled A biopsy is the removal of a sample of tissues for diagnostic purposes. In removing a tumor, it is also common to biopsy a lymph node to test for metastasis, the spread of cancerous tissue from one area to another. To get a better understanding of this, the image below illustrates how cancer cells can originate from a tumor but can colonize and spread to other areas. In this question, since a biopsy is used at the lymph nodes to identify non-lymphatic cancer, we know we are checking for metastasis.

Question #31 All of the following are components of the ear EXCEPT one. Which one of these is the EXCEPTION? A. Pinna B. Malleus C. Cochlea D. Tympanic membrane E. Ciliary body

Ciliary body The ciliary body is a structure located in the eye which has a role with producing the aqueous humor of the eye as well as controlling the eye's lens. Therefore, it is not a component of the

Which of the following describes the relationship between a hummingbird and a flower? A. An opportunistic relationship B. Parallel evolution C. Coevolution D. A commensalism relationship E. A parasitic relationship

Coevolution Coevolution is the evolution of two or more species that reciprocally affect each other. In such a relationship, each organism exerts selective pressures on the other, thereby affecting each other's evolution. In the relationship between a hummingbird and a flower, the hummingbird ensures pollination and in return receives nectar and pollen from the flower. Commensalism - is a relationship between living organisms of two species in which one species obtains food or other benefits like locomotion, shelter, or support from the host species without either harming or benefiting it. This option is incorrect because both organisms benefit in the relationship. Hummingbirds benefit from flowers by collecting pollen and nectar as food for the entire colony. Whereas, flowers use hummingbirds to spread their pollen to help them reproduce.

Which of the following hormones has a function that directly raises metabolism? A. Oxytocin B. Aldosterone C. Thyroid-releasing hormone D. Thyroid-stimulating hormone E. Thyroxine

Thyroxine Thyroid-releasing hormone (TRH) is produced and secreted by the hypothalamus, which induces the anterior pituitary gland to secrete thyroid-stimulating hormone (TSH), which induces the production of Thyroxine (T4) and triiodothyronine (T3), which influence metabolism. Thus, although TRH and TSH are involved in metabolism, their actions are indirect.

Which one of the following features are found in all members of Class Mammalia? A. Fur B. Feathers C. Sweat glands D. Diaphragm E. Quadrate bone

Diaphragm Mammals have very well-developed lungs due to being land-dwelling or having land-dwelling ancestors (the case for the marine mammals including whales). To change the pressure of these lungs to draw air in and push air out, mammals or their mammalian ancestors required a discrete muscle for this role, the diaphragm. In fact, the diaphragm is found in all mammals and is a feature exclusive to only mammals. Note: Other species such as reptiles and amphibians have diaphragm-like structures that vary in importance. The anatomy of those structures also exhibits great variability. Quadrate bone - Mammals have a single lower jaw bone, called the dentary, which is directly attached to the skull. The quadrate bone is found in all non-mammals, for the purpose of forming the lower jaw articulation.

Which of the following is true regarding enzymes? A. Do not change the rate at which equilibrium is achieved B. Increase the activation energy C. Affect the overall energy change of the reaction (ΔG) D. Ensure that the final state of the reaction is the same as the initial state E. Do not change the equilibrium point of a reaction

Do not change the equilibrium point of a reaction Enzymes are macromolecular biological catalysts that accelerate chemical reactions. They allow the reaction to occur faster by taking an alternative reaction pathway that has a lower activation energy. As a result, an enzyme only allows equilibrium to be achieved at a faster rate, and it does not affect the products and reactant concentrations when compared to when no enzyme is present. Just remember, an enzyme does NOT change the free energy (ΔG) of a reaction! And although it does NOT change the equilibrium state or the enthalpy of formation (ΔH), it does INCREASE the rate constant of the forward and reverse reactions! Since Keq = K2/K1, where K1 and K2 are the rate constants of the forward and reverse direction, Keq stays constant even if the individual rates increase due to enzymatic activity

Organisms that belong to the Phylum Chordata possess all of the following structures at some point in their life EXCEPT one. Which one is the EXCEPTION? A. Notochord B. Pharyngeal gill slits C. Dorsal solid nerve cord D. Muscular postanal tail

Dorsal solid nerve cord The Phylum Chordata is extremely diverse and contains all animals that possess at some point in their lives, a hollow nerve cord and a notochord.

Which of the following traits is true of a deuterostome? A. Enterocoelous B. Schizocoelous C. Spiral cleavage D. No archenteron E. Blastopore forms the mouth

Enterocoelous Triploblastic coelomates with bilateral symmetry can be further divided based on the origin of the mouth into protostomes and deuterostomes. In protostomes, the mouth develops at the blastopore and in deuterostomes, the mouth develops at the opposite end of the gut as the anus develops at the blastopore. Another difference between protostomes and deuterostomes is their method of coelom formation. The coelom of protostomes is formed though schizocoely, making protostomes schizocoelous, while the coelom of deuterostomes is formed through enterocoely, making deuterostomes enterocoelous. Enterocoely is a process in which pouches are pinched off the endoderm tissue to develop the mesoderm, expanding the gut and giving rise to the coelom.

Which of the following phylum has radial symmetry? A. Echinodermata B. Arthropoda C. Mollusca D. Porifera

Echinodermata Organisms from the Phylum Echinodermata and Coelenterates display radial symmetry, that is, the body can be divided into five more or less similar portions around a central axis. Some examples of Phylum Echinodermata include starfish and sea urchins. These are examples of animals that are circular and symmetrical in their general shape and could be divided in half along many different lines that pass through their central point, like dividing a pizza in half. Here is an illustration to depict this concept:

What phyla are deuterostomes?

Echinodermata and Chordata

An organism grows more efficiently in oxygen but can also survive in the absence oxygen. What is this organism an example of? A. Obligate aerobes B. Obligate anaerobes C. Facultative anaerobe D. Aerotolerant anaerobes E. Microaerophiles

Facultative anaerobe Facultative anaerobes are organisms that make ATP by aerobic respiration if oxygen is present but are also capable of switching to anaerobic respiration or fermentation if oxygen is absent. For example, bacteria such as E. coli, Staphylococcus spp., and certain fungi are facultative anaerobes. The image below illustrates the different type of organisms that exists in nature:

Where does fertilization occur in humans? A. Uterus B. Ovary C. Cervix D. Fallopian tube E. Seminiferous tubules

Fallopian tube In humans, fertilization takes place in the end of the fallopian tube, specifically in the portion called the ampulla. The fallopian tube links the ovary to the uterus, as shown in the image below. If the fertilized egg travels down the fallopian tube and implants in the uterus, an embryo begins to grow.

Which of the following statements is true about energy use by the body? A. Protein is preferentially utilized as an energy source over fat B. Fats have the greatest yield of ATP C. Most glycogen stores are in muscle D. Fat is preferentially utilized as an energy source over carbohydrates E. Amino acids are converted into glucose for use as an energy source

Fats have the greatest yield of ATP Energy use in the body is highly regulated with various processes being coordinated to optimize energy production as needed. Carbohydrates are utilized preferentially, followed by fats and then proteins. Glucose undergoes glycolysis to form pyruvate, which is converted to acetyl-CoA. Following this is the Kreb's cycle and then oxidative phosphorylation to produce ATP. Based on the body's needs, affected by factors such as exercise and diet, the body may switch to using more fat or protein for energy. The glycerol from a triglycerol can be converted to glucose while fatty acid forms acetyl-CoA which enters the Kreb's cycle. This is known as beta-oxidation. During beta-oxidation of saturated fatty acids, each cut producing two carbon molecules produces one NADH and one FADH2 with one less FADH2 molecule for any double bond if unsaturated. This results in a very high yield of ATP by fats compared to carbohydrates.

In organisms such as birds and reptiles, the yolk sac contains nourishing yolk. However, in humans the yolk sac serves a different purpose. Which of the following is its purpose in humans? A. Food storage site for embryo B. First site of red blood cell synthesis C. Site to excrete wastes D. Site for white blood cell synthesis E. Oxygen transport

First site of red blood cell synthesis The yolk sac is a membranous sac attached to an embryo formed by cells of the hypoblast next to the embryonic disk. It acts as the preliminary circulatory system. In the early fetus, red blood cell synthesis takes place in the mesodermal cells of the yolk sac. It is the first site of blood formation. Subsequently, this process moves to the liver and then the bone marrow. The image below illustrates the yolk-sac of a human embryo.

The cortical reaction directly functions by A. Formation of a fertilization membrane B. Generation of a nerve-like impulse by the egg cell [ C. Production of a fast block to polyspermy D. Fusion of egg and sperm nuclei E. Release of hydrolytic enzymes from the sperm cell

Formation of a fertilization membrane A cell resulting from polyspermy contains three or more copies of each chromosome, one from the egg and one each from multiple sperm. This usually results in an inviable zygote. However, mechanisms known as fast and slow block occur to prevent polyspermy. 1. A cortical reaction is part of the "slow-block" component of polyspermy, which creates a non-penetrable fertilization membrane by secreting cortical granules that prevents multiple sperms from fertilizing the same egg. The cortical reaction occurs due to calcium oscillations inside the oocyte, as shown in the image below. 2. The fast block of polyspermy, on the other hand, immediately but temporarily blocks additional sperm from fertilizing the egg. In the egg, Na+ channels open in the plasma membrane. Normally, Na+ concentration is higher outside the cell than inside, so Na+ ions flow down their gradient into the egg and the plasma membrane depolarizes. This depolarization causes the fast block to polyspermy.

A random group of 200 black bears dissociate from a bigger population and settle in a region 100 km away. It is observed that the smaller group, along with their future generations, have a different fur type than the original population. What best describes this phenomenon? A. Gene flow B. Heterosis C. Bottleneck Effect D. Outbreeding E. Founder's effect

Founder's effect The question stem poses a scenario in which a subpopulation with different genetic material is separated from the main population. This points to either gene flow or genetic drift as these are causes of change in allele frequency within a population. The key term that differentiates the gene flow and genetic drift is the word "random". Genetic drift is due to random flow of alleles (in this case, fur type), as outlined in this question. Founder's effect and bottleneck effect are both types of genetic drift. However, bottleneck effect describes allele frequency change due to catastrophic events, which is not mentioned in the question stem. This makes Option E. Founder's effect, a type of genetic drift, the correct answer.

DNA fragments produced by restriction enzymes can be separated from one another using A. Centrifugation B. PCR C. Vortexing D. SDS-PAGE E. Gel electrophoresis

Gel electrophoresis Gel electrophoresis is a biological lab technique used to separate charged molecules, such as DNA fragments, according to size. Since the question states that restriction enzymes are used to produce DNA, we know that these enzymes have cut the DNA molecules at specific places to form DNA fragments of various sizes. Using gel electrophoresis, we can then separate these DNA fragments according to size. DNA samples are loaded into wells at one end of the gel, and then an electric current is applied to move the fragments through the gel. DNA fragments are negatively charged because of the phosphate groups in their sugar-phosphate backbone, so they move towards the positive electrode where smaller fragments move through the gel faster than larger ones.

Which is TRUE of the hardy-Weinberg principle? A. Gene flow is necessary to maintain equilibrium B. Mating patterns do not affect frequency of alleles in a population C. Genetic equilibrium requires lack of evolution D. Genetic equilibrium can only be assumed for one year of life E. The "2pq" expression accounts for natural selection

Genetic equilibrium requires lack of evolution In order for the genetic equilibrium to remain, the following conditions must be met: • No Natural Selection • No Mutation • No gene flow (the population is isolated from others) • No genetic drift (No founder effect or bottleneck effect!) • Random Mating

All of the following are cell types found in the stomach EXCEPT one. Which one is the EXCEPTION? A. Mucous cells B. Chief cells C. Parietal cells D. G Cells E. Goblet Cells

Goblet Cells Within the folds of the stomach are gastric glands containing various types of cells. Mucous cells secrete mucous which serve to protect the lining of the stomach from the highly acidic juices of the stomach. Parietal cells secrete hydrochloric acid, which denatures proteins and kills bacteria. Chief cells secrete pepsinogen and gastric lipase. G cells secrete the hormone gastrin. It is important to note that gastrin stimulates parietal cells to secrete hydrochloric acid which activates the pepsinogen to pepsin. Pepsin then digests proteins found in food. Furthermore, goblet cells are found within the small intestine where they secrete mucous as a protective layer.

The first living organisms to appear on Earth were: A. Protobionts B. Heterotrophic prokaryotes C. Unicellular eukaryotes D. Photosynthetic prokaryotes E. Autotrophic archaea

Heterotrophic prokaryotes 1. The early atmosphere formed due to the release of various chemicals into the atmosphere due to volcanic activity. This material included CH4, NH3, CO, CO2, H2, N2, H2O, S, HCl, HCN, with little to no oxygen to form, according to Oparin and Haldane, a reducing atmosphere. As proven by the Miller-Urey experiments various simple organic molecules include the monomers of amino acids resulted except for nucleic acids. These monomers randomly combined into inorganically produced polypeptides known as proteinoids. 2. Gradually, organic molecules concentrated in non-reproducing protocells known as protobionts. Like cells, they contained organic material contained within a lipid membrane that would undergo reactions and some semblance of metabolic activity. It is also speculated that the earliest nucleotides formed spontaneously before combining into RNA that conferred both genetic code and enzymatic activity. In contrast to the more stable DNA due to the lack of oxygen on the 2' carbon position, RNA is found only in single strands and can fold into complex three-dimensional shapes much like proteins. 3. From RNA and protobionts, the simplest heterotrophic prokaryotes arose. They were likely heterotrophic it is much simpler for a cell to take in foreign organic material for food than to synthesize its own from inorganic material. 4. Only later did the more complex autotrophic prokaryotes arise with the machinery necessary to convert inorganic material into organic material. The byproduct, oxygen then converted the earth's atmosphere from a reducing one to an oxidizing one. Later, some prokaryotes took residence in other prokaryotes to form eukaryotes. The energy-producing organelles, mitochondria and chloroplasts, resemble prokaryotes due to their having their own circular DNA, prokaryote-like ribosomes, reproduction by binary fission, and double membranes. Based on the origins of life, the living organisms that were the earliest to arise were

Which of the following are ways that cells directly communicate with each other? I. Transcription factors II. Chemical signals III. Neurotransmitters

II. Chemical signals III. Neurotransmitters Cell-cell communication can occur different ways. One method you may be aware of is chemical signals, which can occur via neurotransmitters at cell junctions as seen via acetylcholine or hormones (example glucagon/insulin) in order to travel long distances throughout the blood. However, whenever the chemical signal used to communicate between cells is hormonal, it passes through the cell membrane and causes various reaction cascades. In this process, transcription factors are activated which cause either the inhibition or up-regulation of various proteins. The change in the intracellular environment can change the way a cell can respond to the extracellular stimuli. Thus, transcription factors are used as an INDIRECT method of cellular communication.

A cancer researcher wants to track a p53 protein related to tumor suppressor functions. Which technique could be used to locate this p53 protein within a cell? A. ELISA B. Polymerase Chain Reaction C. Immunofluorescence staining D. Microarrays E. Western blotting

Immunofluorescence staining Immunofluorescence staining is a genetic technology where a protein is tagged with a fluorescent amino acid or molecule in order to visualize target proteins. Different techniques and tags can allow researchers to selectively locate and visualize specific proteins using a fluorescence microscope, as shown in the image below. Therefore, Option C. Immunofluorescence staining, is the correct answer as it can be used to locate the p53 protein. Western blotting - Western blotting is an in vitro technique for studying the presence of proteins, that is, it takes place outside of a cell. Therefore, this option is incorrect. Western blotting aims to detect specific proteins by denaturing them, attaching negative charge, then performing electrophoresis. The desired protein, if present in the sample, will move a known distance due to having a known length. Antibody tags are then used to visualize exactly where the protein has moved to in the gel.

A virus infects the eye of a dog, selectively damaging the rod cells. Which of the following would be expected as a result? A. Inability to see dim light B. Inability to see colours C. Inability to see in bright light D. Inability to see far distances E. Inability to see near distances

Inability to see dim light Rods are a type of photoreceptors within the retina that are necessary for night-vision and vision in dimmer lighting. They mainly occupy the outer edges of the retina. They contain pigments called rhodopsin, which undergo chemical change when exposed to light rays and cause these photoreceptor cells to signal bipolar cells near the retina, in order to send signals to the brain through the optic nerve. Therefore, a defect in rod cells would impair the ability to see in dim lighting.

A parathyroid tumour, leading to hyperparathyroidism, would cause which of the following symptoms? A. Increased bone fractures B. Decreased reabsorption of calcium in the kidneys C. Decreased serum calcium concentration D. Greater osteoblastic activity E. Increased calcium secretion in the kidneys

Increased bone fractures The parathyroid glands are located near the thyroid gland. A parathyroid tumor would cause hypertrophy of the gland and hyper-secretion of the parathyroid hormone (PTH). PTH is responsible for increasing serum calcium levels. One way this is done is by increasing the osteoclastic activity because osteoclasts degrade bone to release calcium as shown in the image below. Therefore, an abnormally high amount of PTH would mean abnormally high osteoclastic activity, which means more bone degradation, and an increased chance of bone fracture. Furthermore, PTH also induces increased reabsorption of calcium in the kidneys and the intestines

Osteoporosis is a disease that causes excessive bone resorption in individuals suffering from it. This excessive bone resorption can lead to A. Decreased calcium levels B. Increased phosphorus levels C. Increased parathyroid hormone levels D. Decreased calcitonin levels

Increased phosphorus levels One crucial role of the skeletal system is to store minerals that are required by the body to properly function. Two prominent minerals that make up the bone matrix are calcium and phosphorus; these minerals can be released back into the bloodstream when bone resorption occurs. Bone resorption is the breakdown of bone by osteoclasts. When blood calcium levels are low, parathyroid hormone (PTH) is released and stimulates osteoclasts to breakdown bone to release calcium and phosphorus. As blood calcium levels return to normal, negative feedback inhibits the release of PTH. When blood calcium or phosphorus levels are high, calcitonin is released to inhibit bone resorption as shown in the image below.

What is an agent that is made and released in response to viruses? A. Pyrogens B. Interleukins C. Interferon D. Endotoxin E. Antigens

Interferon Interferons are released by cells that are infected by a virus to promote the neighboring cells to produce virus-fighting proteins.

hich of the following signalling molecule is used in the immune response to stimulate the development and activation of lymphocytes? A. Immunoglobulin B. Interferon C. Heparin D. Perforin E. Interleukin

Interleukin The cytokines are a class of small proteins that play various roles in cell signalling. Two of the cytokines involved in the immune response are interleukins and interferons. Activated helper T cells will produce interleukins to indicate to other immune cells that there is a pathogen. These interleukins stimulate the proliferation of the T and B lymphocytes, and as well as macrophages. Therefore, Option E. Interleukins, is the correct answer.

Pepsinogen is a zymogen secreted by the stomach. All of the following statements are true about pepsinogen EXCEPT one. Which one is the EXCEPTION? A. It catalyzes the hydrolysis of peptide bonds B. Pepsin is the active form C. It must be activated for digestion D. It is a proenzyme E. It is activated by cleavage

It catalyzes the hydrolysis of peptide bonds A zymogen, also known as a proenzyme, is the inactive form of an enzyme. Many enzymes are synthesized in their inactive form and then are activated when they reach their target tissue. For example, the zymogen pepsinogen is the inactive form of pepsin. Pepsinogen is secreted by chief cells in the mucosal layer of the stomach. Once it is secreted into the stomach lumen, the hydrochloric acid causes it to cleave itself into its active form pepsin. Pepsinogen is produced instead of pepsin because pepsin is a very strong endopeptidase; if chief cells secreted pepsin, the mucosal layer would be damaged as the pepsin moved along the lumen. As such, the correct answer for this question is Option A. It catalyzes the hydrolysis of peptide bonds. Since pepsinogen is a zymogen, it is inactive and cannot catalyze any reactions; in other words, it must be activated before it can perform enzymatic functions.

What characteristics do all organisms in the kingdom monera share? A. Have a cell wall made of chitin ] B. Have cells with membrane-bound organelles C. Lack mitochondria D. Have a cell wall made of cellulose E. Are heterotrophic

Lack mitochondria Monera: This kingdom includes all (and only) prokaryotic organisms. Some characteristics of prokaryotes include being unicellular, having a cell wall made of murein (peptidoglycan), and being either heterotrophic or autotrophic. Examples of organisms in kingdom monera are bacteria and cyanobacteria. Protista: This kingdom includes simple eukaryotic organisms that can be unicellular, colonial, or multicellular. Some share similar characteristics with organisms in kingdom animalia, plantae, or fungi. They can be heterotrophic or autotrophic. Some examples of protists are algae, plankton, and slime molds. Fungi: This kingdom includes heterotrophic, eukaryotic organisms that have a cell wall made of chitin. Some examples of fungi are mushrooms, yeasts, and molds. Plantae: This kingdom includes multicellular eukaryotic organisms that have a cell wall made of cellulose. Most plants are capable of photosynthesis and are therefore mostly autotrophic. Some examples of plants are trees, shrubs, and flowering plants. Animalia: This kingdom includes multicellular eukaryotic organisms that are heterotrophic; also, the cells of an animal all lack a cell wall. Most animals require oxygen and the consumption of organic material to produce energy via cellular respiration. Examples of animals include insects, mollusks, and crustaceans.

Which part of the digestive system functions to absorb water, electrolytes, and bacteria-produced Vitamin K? A. Stomach B. Ileum C. Large intestine D. Duodenum E. Jejunum

Large intestine The main functions of the large intestine are the absorption of water, electrolytes, and vitamins. Therefore, Option C. Large intestine, is the correct answer.

Organisms can only convert energy from one form into another according to the first law of thermodynamics. Which of the following would be the ultimate source of energy for all living organisms? A. Nuclear reactions occurring between atoms B. Light energy from the sun C. ATP produced by Krebs cycle D. Chemical energy released by cells at the microscopic level E. Chemical energy released from glucose

Light energy from the sun The sun is the major source of energy for organisms and the ecosystems of which they are a part. Producers, such as plants and algae, use energy from sunlight to make food energy by combining carbon dioxide and water to form organic matter. This process begins the flow of energy through most, if not all, food webs. In a way, food is sunshine stored in chemical form. Organisms use the stored energy in food to fuel all living processes. Remember, the sun provides energy for all life on Earth to sustain due to the light it emits. This light in turn fuels photosynthesis and other biological processes on earth. Therefore, the "light energy from the sun" (Option B.) is the best answer compared to the other options

Which of the following areas of the brain is incorrectly associated with its function? A. Cerebellum: motor control & balance B. Amygdala: memory consolidation C. Medulla: breathing & heart rate D. Limbic System: eye-hand coordination E. Occipital lobe: visual processing

Limbic System: eye-hand coordination The only brain area and function pair incorrectly associated is the Limbic System and eye-hand coordination. The Limbic System is involved in emotional and memory processing. The Limbic System consists of various brain structures, three of the most important being the hippocampus, the amygdala, and the hypothalamus, which are shown in the figure below.

In the fetal circulatory system, the ductus venosus allows blood to bypass which of the following? A. Pulmonary circulation B. Systemic circulation C. Placenta D. Liver E. Right ventricle

Liver As oxygenated and nutrient-rich blood returns to the fetus from the placenta via the umbilical vein, half enters the ductus venosus. This bypasses the liver as blood returns to the heart. The liver in adults acts to filter and detoxify the blood but is not fully functional during early development. The image below illustrates the main components of the fetal circulatory system, including the ductus venosus. Pulmonary circulation - This option is incorrect because it is the foramen ovale that allows pulmonary circulation to be bypassed by bypassing the right ventricle, as well as the ductus arteriosus which conducts blood from the pulmonary artery to the aorta.

A scientist discovers a new species that produces highly concentrated urine. Which of the following structure would the organism contain that may explain this? A. Shorter proximal convoluted tubules B. Longer proximal convoluted tubules C. Shorter Loops of Henle D. Longer Loops of Henle E. Larger Bowman's capsules

Longer Loops of Henle The loop of Henle (both ascending and descending) is involved in creating a countercurrent multiplier where the kidney actively produces a solute gradient in order to produce a high solute concentration in the medulla, which allows for water retention in the distal portion of the loop of Henle. Thus, the longer the loop of Henle, the greater the concentration gradient will be between the loop of Henle and the medulla, which results in a greater amount of water to be resorbed and thus creating a more concentrated urine.

What can be a sign of damaged juxtaglomerular cells in the kidney? A. High levels of cortisol B. Decreased urine production C. Low blood pressure D. Low levels of blood urea E. Formation of kidney stones

Low blood pressure Blood is filtered in the glomerulus by high hydrostatic pressure, which forces excess fluid and waste products into Bowman's space. Circulating blood enters the glomerulus through the afferent arteriole and exits through the efferent arteriole. The juxtaglomerular cells in the kidney are located next to the glomerulus (juxta = near/beside) and are derived from the smooth muscle cells of the afferent arteriole. When pressure is low in the afferent arteriole (due to a drop in blood pressure of the body), the juxtaglomerular cells respond by releasing renin. Renin activates the renin-angiotensin-aldosterone system

All of the following contribute to the circulation of lymph throughout the body EXCEPT one. Which one is the EXCEPTION? A. Location of re-entry B. Smooth muscle contractions C. Skeletal muscle contractions D. Lymph node contractions E. Lymphatic valves

Lymph node contractions The heart pumps blood throughout the body, and it pumps so powerfully that it actually squeezes some lymph out of the capillaries. The lymphatic system collects excess fluid in the interstitial space and returns this to the circulatory system. The lymphatic system is able to pump this lymphatic fluid in one direction due to the following reasons: 1. Point of re-entry - Lymph is intelligent about where it reenters the high-pressure system. It particularly reenters at the very end of the venous circulation system as the pressure there is much lower than the pressure in the arteries or capillaries. 2. Lymphatic valves - There are structures within the lymph vessels that prevent fluid from going back. 3. Smooth and Skeletal muscle contractions - These initiate motion and drive the fluid in one direction. Pro-Tip: For the DAT, it is important to know that lymph circulation is primarily driven by skeletal muscle contractions.

All of the following are characteristics of epigenetics EXCEPT one. Which one is the EXCEPTION? A. Modifies nucleotide sequence B. Heritable C. Contributes to phenotypic variability D. Influences gene expression E. May result from external or environmental factors

Modifies nucleotide sequence Epigenetics involves heritable phenotypes that result from changes to the genome without modifying the nucleotide sequence. These changes include the following: 1. DNA modifications: DNA Methylation: Addition of methyl groups that silences genes, leading to lower expression. 2. Histone modifications: Histone Acetylation: Addition of acetyl groups that promote gene expression. Histone Deacetylation: Removal of acetyl groups that reduces gene expression. Histone Methylation: Addition of methyl groups that may increase or decrease expression depending on methylation site and quantity. Source: https://commons.wikimedia.org/wiki/File:Epigenetic_mechanisms.png#/media/File:Epigenetic_mechanisms.png DNA's sugar-phosphate backbone has a negative charge due to the phosphate groups. Histone's positive charge causes electrostatic attraction that allows DNA to wind around histones. Acetylation of these histones removes this positive charge which removes electrostatic attraction and lets DNA unwind, promoting expression. Etymology: Epi- means above just as epidermis refers to the layer above the dermis. So epigenetic literally means above the genome rather than inside the genome as in the nucleotide sequence. DNA methylation places methyl groups above the DNA, outside of the coil.

Which of the following organisms is most similar in taxonomic categorization to yeast? A. Slime molds B. Amoeba C. Dinoflagellates D. Blue-green algae E. Mushroom

Mushroom Both yeast and mushrooms are members of the kingdom Fungi. With regards to cell count, there are unicellular fungi (ex. yeast) and multicellular fungi (ex. mushroom). Therefore, Option E. Mushroom, is the correct answer. Fungi are characterized by a chitin cell wall and are saprophytes that rely on extracellular digestion of biomass prior to absorption. Slime molds - Slime moles are only superficially related to fungal molds but are otherwise not related to fungi. Therefore, this option is incorrect. Rather, slime molds are part of a group of fungi-like protists (one of the Eukaryotic kingdoms). They are capable of living as single cells but can aggregate into groups that make them resemble fungal molds.

Immobile sperm can cause infertility. Which of the following may possibly explain this phenomenon? A. Lack of intermediate filaments B. Mutation in tubulin C. Displacement of zona pellucida D. Excessive mitochondria E. Dysfunctional kinesin

Mutation in tubulin Motility is important to sperm cells in order for them to be able to reach an egg and fertilize it. What gives a sperm cell its motile abilities is its tail, also known as a flagellum, which moves in quick, wave-like motions that help propel the sperm cell forward. The eukaryotic flagellum is composed of a bundle of microtubules, which are polymeric structures made up of the monomer protein tubulin, as shown in the image below. Mutations in tubulin could have adverse effects on the assembly of microtubules, and thus in turn on the proper formation and function of sperm cells' flagella, which could reduce or completely hinder sperm cells' motility.

A long-distance runner has been running for several days through a desert without any food. After the muscles in her legs are completed of all ATP, which of the following would best describe the state of her muscular filaments? A. Myosin head is detached from actin but not in the position for the next contraction B. Myosin head is attached to actin and ready for a power stroke C. Myosin head is attached to actin immediately after a power stroke D. Myosin head is detached from actin and ready to form another cross bridge E. Myosin head is detached from actin as tropomyosin is blocking attachment site on actin

Myosin head is attached to actin immediately after a power stroke Muscle tissues require the presence of ATP in order to reset and perform additional muscle contraction. Specifically, as seen in step d) in the diagram below, ATP causes the detaching of the myosin head from actin filaments immediately proceeding the completion of the power stroke, allowing the myosin head to return to its original position ready for the next power stroke. In conditions where there is no ATP, specifically termed rigor mortis, the myosin head cannot detach from actin following a power stroke, leaving the muscle in a rigid and contracted state

All of the following were synthesized during the Miller-Urey experiment EXCEPT one. Which one is the EXCEPTION? A. Carbon monoxide B. Amino acids C. Several fatty acids D. Aldehydes E. Nucleic Acids

Nucleic Acids The Miller-Urey experiment was a chemical experiment that simulated the conditions thought at the time to be present on early Earth, and tested the chemical origin of life under those conditions. American chemists Harold Urey and Stanley Miller, combined warm water with water vapor, methane, ammonia and molecular hydrogen. These were then pulsed with electrical discharges. These components were meant to simulate the primitive ocean, heat, lighting, and the prebiotic atmosphere. A week later they found that simple organic molecules such as amino acids had formed. In addition to amino acids, they found several fatty acids, carbon monoxide and aldehydes as well. Thus the Miller-Urey experiment successfully produced molecules from inorganic components thought to have been present on prebiotic earth. The image below shows the setup of the experiment. A closed system can be observed in the image into which Miller pumped a mixture of gases (methane, ammonia and hydrogen). In order to add water vapor to the mixture, there was a flask of boiling water, and the gases were circulated around the apparatus. The gaseous mixture was subjected to a high voltage electrical discharge and then passed through a condenser to cool it down before going through a portion of the tube cooled in ice to collect any liquid products.

Which of the following types of cells resorb bone matrix? A. Osteoblasts B. Osteoclasts C. Osteocytes D. Osteons E. Chondroblasts

Osteoclasts Bone matrix is made up of various substances, including calcium, collagen, and water. Bone is continually created, broken down, and remodeled. Components of the matrix are produced by cells known as osteoblasts. In other words, osteoblasts are responsible for the process of laying down new bone material in a process known as ossification. Osteocyte cells play a maintenance role and can also build bone. Osteoclast cells are involved in resorption of bone by releasing acid and enzymes to break down components of the matrix, and they then engulf and digest fragments. Matrix cells have a common naming convention. Cells ending in "-blast" build matrix (blast = build), "-cyte" cells are involved in maintenance, and "-clast" cells are involved in breakdown. For example, chondroblasts produce the matrix of cartilage.

All of the following are characteristics of IgG antibodies EXCEPT one. Which one is the EXCEPTION? A. Has two heavy and two light chains B. Heavy and light chains connected via disulfide bonds C. Involved in passive immunity of fetus D. Participates in opsonization E. Pentameric structure

Pentameric structure As shown in the image above, IgD, IgE, and IgG are monomers. A monomer consists of a single subunit. Each subunit consists of 2 heavy and 2 light chains that are linked together with disulfide bonds. In contrast, IgA is a dimer consisting of two subunits, whereas IgM is a pentamer consisting of five subunits.

What organelle contains enzymes that produce hydrogen peroxide as a by-product essential for lipid breakdown? A. Peroxisomes B. Lysosomes C. Nucleus D. Mitochondria E. Endoplasmic reticulum

Peroxisomes Peroxisomes are membrane-bound organelles that are found in the cytoplasm of eukaryotic cells. They play a key role in the oxidation of specific biomolecules. For example, a major function is the breakdown of fatty acids through beta-oxidation. Peroxisomes contain oxidative enzymes such as D-amino acid oxidase and uric acid oxidase, which use molecular oxygen to remove H+ atoms from specific organic substrates in an oxidative reaction, producing hydrogen peroxide. H2O2is toxic, however, another peroxisomal enzyme, called catalase uses this H2O2 to oxidize other substrates.

A defect in what structure of a plant would prevent an ovule from being produced? A. Stigma B. Pistil C. Stamen D. Sepal E. Peduncle

Pistil Pistil is the female reproductive structure of flowering plants (i.e angiosperms) that produces the ovule. Therefore, a defect in the pistil would prevent the plant from producing an ovule.

An earthquake demolishes a rabbit population and the remaining population has shorter ears on average than the initial population. If short ears is genetically determined, what has this rabbit population experienced? A. Directional selection B. A founder effect C. Population bottleneck D. Mutation E. Natural selection

Population bottleneck Population bottleneck events occur whenever a population shrinks and the remaining phenotypes are different than the original population. The bottleneck may be caused by various events, such as an environmental disaster, the hunting of a species to the point of extinction, or habitat destruction that results in the deaths of organisms. Such events can reduce the variation in the gene pool of a population. This leads to a smaller population, with a smaller genetic diversity, which is able to pass on genes to future generations of offspring through sexual reproduction. As in the case of the rabbits, only the rabbits that survived (short eared rabbits) passed on their genes to their offspring which lead to rabbits having shorter ears on average. Genetic diversity remains lower, increasing only when gene flow from another population occurs or very slowly increasing with time as random mutations occur. The image below illustrates the concept of a population bottleneck.

Which of the following is the product(s) of glucose catabolism in glycolysis? A. PGAL B. H2O and CO2 C. Pyruvate and CO2 D. Acetyl CoA E. Pyruvate

Pyruvate Glycolysis is a catabolic process in which six-carbon glucose molecules are oxidized and broken down into pyruvate molecules. It is the first step in the breakdown of glucose to extract energy for cellular metabolism. During this process, 2 ATP, 2 NADH, and 2 pyruvate molecules are formed, as shown in the image below.

Which of these is involved in the polyspermy blocks? A. Hyperpolarization B. Intracellular sodium release C. Extracellular calcium influx D. Release of cortical granules E. Synthesis of ZP3

Release of cortical granules The fast and slow blocks of polyspermy are necessary to prevent polyploidy. These blocks work to make the fertilized egg impenetrable against additional sperm. First, let us review the process of fertilization. After sperm is activated by capacitation, the flagella become hyperactive and the acrosome is more permeable. When the sperm penetrates the outer corona radiata to bind to the ZP3 protein of the zona pellucida, mutual recognition occurs. This binding to ZP3 allows the acrosomal reaction to occur. The digestive enzymes in the acrosome degrade the zona pellucida to allow the sperm's membrane to merge with that of the egg, depositing the sperm's nucleus in the egg. The integration of the sperm's nucleus with the egg's nucleus now results in a diploid cell known as a zygote. 1. The fast block of polyspermy results from the rapid influx of extracellular Na+ following the binding of a sperm with the ZP3 protein. This Na+ influx causes depolarization of the egg that repels additional sperm. This fast block is very rapid because it only involves opening Na+ ion channels. However, the diffusion of Na+ from the egg's cytoplasm means the depolarization is relatively short-lived. 2. The slow block of polyspermy creates are more long-lasting effect and is stimulated by the depolarization of the fast block. This depolarization causes the release of intracellular stores of Ca2+ into the cytoplasm which then leads to the exocytosis of the enzymes of the cortical granules into the space between the plasma membrane and zona pellucida. These enzymes digest proteins that hold the two together and inactivates ZP3 proteins. The separated zona pellucida develops into the sperm-impermeable fertilization envelope.

Which of the following is a function of the lymphatic system? A. Transport fats towards the digestive system B. Return fluids that have escaped from blood vessels C. Transport of non-fat nutrients towards target cells D. Synthesis of erythrocytes E. Take up particles except larger proteins

Return fluids that have escaped from blood vessels The lymphatic system is the open, secondary circulatory system responsible for taking up excess interstitial fluid and returning it to the primary circulatory system via the thoracic duct and right lymphatic duct to the left and right subclavian veins respectively. The image below illustrates the essential components of the human lymphatic system along with its function of draining fluid away from tissues. Due to lower pressure and reliance on skeletal muscle contractions to flow, the lymphatic system has valves to prevent backflow. The lymphatic system also plays a role in transporting fats away from the digestive system and in immunity. In addition, the lymphatic system also contains the lymph nodes which are rich in lymphocytes that monitor the lymph for pathogens.

Suppose that radioactively labeled uracil are added to a test tube containing eukaryotic cells that are actively dividing. Which of the following cellular structures would the radioactively labeled uracil be incorporated in? A. Chromosomes B. Peroxisome C. Nuclear membrane D. Ribosomes E. Golgi apparatus

Ribosomes Uracil (U) is one of the four nitrogenous bases found in RNA. However, uracil is the only nitrogenous base is exclusively found only in RNA. It is a pyrimidine and forms a base pair with Adenine (A). In DNA, Uracil is replaced by Thymine (T), a methylated form of Uracil. Furthermore, ribosomes are cellular structures that serve as the site of protein synthesis and are composed of a complex of RNA (ribosomal rRNA) and proteins, as shown in the image below. Therefore, it would be expected to see radioactively labelled Uracil incorporated into rRNA, and thus into ribosomes.

Which of the following is INCORRECTLY matched: A. Cardiac muscle - functional syncytium B. Skeletal muscle - multinucleated C. Smooth muscle - somatic innervation D. Skeletal muscle - striated E. Cardiac muscle - gap junctions

Smooth muscle - somatic innervation To answer this question, it is important to know that there are THREE types of muscles: • Skeletal muscle is comprised of multinucleated cells that form a syncytium. It is striated and innervated by the somatic nervous system. • Cardiac muscle is also striated, but is innervated by the autonomic nervous system. It is mononucleated or binucleated and exhibits properties of a functional syncytium due to its intercalated discs. • Smooth muscle is mononucleated but not striated. It does not form a syncytium, and it is innervated by the autonomic and the enteric nervous system.

The role of the collecting duct in the urinary system involves A. Sodium reabsorption in response to aldosterone B. Secretion of drugs, toxins and some ions C. Reabsorption of glucose and amino acids D. Secretions of hydrogen ions and sodium ions E. Glucose reabsorption in response to vasopressin

Sodium reabsorption in response to aldosterone The kidneys are composed of functional units called nephrons. In nephrons, the glomerular capillaries, Bowman's capsule, the renal tubule, and the collecting duct work together to filter blood and concentrate the waste products as urine. The collecting duct is the last component of the nephron. Unless stimulated, the collecting ducts do not allow for the reabsorption of water, thus resulting in more dilute urine. However, once either aldosterone or antidiuretic hormone/vasopressin is stimulated, the collecting duct becomes permeable and allows for the retention of water. This in effect leads to more concentrated urine. Although they both function in water reabsorption, the mechanism of aldosterone and vasopressin are different. Aldosterone is a mineralocorticoid that is released by the adrenal gland (more specifically, the adrenal cortex). It functions by excreting potassium and hydrogen ions while reabsorbing sodium ions. This creates an osmotic gradient which allows for the absorption of water. In comparison, vasopressin is a hormone that is synthesized by the hypothalamus and is released from the posterior pituitary. It functions in the up-regulation and incorporation of water channels termed aquaporins. These hydrophilic channels facilitate the water uptake and thus lead to more concentrated urine.

Allopatric speciation is best described as which of the following? A. Speciation that occurs after a population is divided geographically B. Many species evolve when a single species is introduced to an area with diverse niches C. Possession of more than the normal set of chromosomes leading to reproductive isolation D. Speciation that occurs without the presence of a geographic barrier E. Two unrelated species evolve analogous features

Speciation that occurs after a population is divided geographically Speciation is the process by which new species are formed. When a geographic barrier is present and interbreeding between the two populations is prevented, the gene frequencies of each population can change over time. This may occur due to natural selection, genetic drift, or mutations. If divergence is sufficient such that if the barrier was removed the two populations do not interbreed, a new species has formed. This is called allopatric speciation, which can occur through two possible ways: 1. Dispersal: populations are at different locations 2. Vicariance: populations are separated by geographic barrier but are in same location

Which of the following is the product of spermatogenesis? A. Primary spermatocytes B. Spermatogonia C. Secondary spermatocytes D. Spermatids E. Spermatozoa

Spermatozoa Spermatogenesis is a process that begins at puberty in males and occurs within the seminiferous tubules in the testes. Spermatogonia cells undergo mitosis to form primary spermatocytes. These then undergo meiosis. Meiosis I produces two secondary spermatocytes, and meiosis II then gives four spermatids. Spermatids are then nourished by Sertoli cells and they develop into spermatozoa, also known as sperm. This process is called spermiogenesis and is a part of spermatogenesis. Sperm cells are then released, which is called spermiation. Spermatids - This option is incorrect because spermatids are present prior to spermiogenesis, the final step of spermatogenesis.

Which of the following layers of the skin is responsible for the production of new skin cells? A. Stratum germinativum B. Stratum spinosum C. Stratum corneum D. Stratum lucidum E. Stratum granulosum

Stratum germinativum The deepest layer of the epidermis known as Stratum germinativum (also known as Stratum Basale), consists of a single row of stem cells that continually divide to give rise to new stem cells. Of the two daughter cells produced from each mitotic division, one cell remains in the basal layer to continue dividing while the other begins differentiating into a mature skin cell known as a Keratinocyte. As constant cell division pushes the skin cells outward through the epidermal layers, they fill with keratin, flatten, and lose their organelles.

The golgi apparatus lacks the ability to perform which of the following functions? A. Packaging proteins B. Modifying proteins C. Synthesizing proteins D. Producing lysosomes

Synthesizing proteins The Golgi apparatus is an organelle found in eukaryotic cells. It is part of the endomembrane system in the cytoplasm and has the following functions: • Packages proteins into membrane-bound vesicles • Processes proteins that are synthesized in the cell • Involved in the transport of lipids around the cell • Involved in the creation of lysosomes The Golgi apparatus has many folds; typically there are five to eight folds. The organelle also has a cis-Golgi and trans-Golgi network, as shown in the image below. Vesicles from the endoplasmic reticulum fuse with the cis-Golgi network and subsequently progress through the organelle to the trans-Golgi network, where they are packaged and sent to the required destination. The cis and trans area can be seen in the figure below. proteins are synthesized by ribosomes, not the Golgi apparatus.

Adaptive radiation is best described as A. The emergence of multiple lineages from a single ancestral species B. Process where a species can produce more offspring C. Radiation that prevents a species from adapting to an environment D. Process in which a species best adapts to its environment E. The emergence of an adapted species over one generation

The emergence of multiple lineages from a single ancestral species Adaptive radiation is a process in which multiple diverse species evolve rapidly from one ancestral species. It occurs when members of the ancestral species start occupying different niches with different environmental conditions, triggering these members to evolve in order to adapt to their new environment. The most well-known example of adaptive radiation is finch speciation on the Galapagos islands. Adaptive radiation tends to take place under the following conditions: 1. A new habitat has opened up: for example, a volcano can create new ground in the middle of the ocean. An extinction event could also effectively achieve this same result, opening up niches that were previously occupied by species that no longer exist. 2. This new habitat is relatively isolated. 3. The new habitat needs a wide availability of niche space.

The stages of embryonic development

The immediately fertilized egg is known as the zygote and is a single cell which then undergoes cleavage. This rapid cleavage without an increase in the size of the overall mass of cells produces cells called blastomeres. At the 16 cell stage, the solid, ball-like morula is formed. Further division produces a hollow, 128 cell blastula. Further division of the blastula produces the blastocyst that consists of an outermost trophoblast that forms the extraembryonic membranes and the inner cell mass that develops into the embryo.

The allele for being left-handed is recessive. What is the probability that a child will be left-handed and have type O blood if the mom is left-handed and has type AB blood, and the dad is right-handed (heterozygous) and has type O blood?

There are three possible alleles that can be inherited to determine blood type: A, B and O. The A and B alleles are codominant, meaning they are expressed together if both alleles are present. A person with type AB blood has the A and B allele. In contrast, the O allele is recessive; a person can only have type O blood if one O allele is inherited from each parent. A Punnett square can be used to determine the probability of the child having type O blood: OO x AB = AO BO AO BO

A population of 100 lizards exists in Hardy-Weinberg equilibrium in which the lizard's allele for short tail is dominant, and the allele for long tail is homozygous recessive. If 16 lizards were found to have long tails within a population, what is the allele frequency for lizards that have short tail?

To solve this question, we must use the Hardy-Weinberg principle and its equations: p2 + 2pq + q2 = 1 p + q = 1 Where p is the frequency of the 'L' (dominant short tail) allele, and q is the frequency of the 'l' allele (recessive long tail) in the population. In the equation, p2 represents the frequency of the homozygous genotype LL, q2 represents the frequency of the homozygous genotype ll, and 2pq represents the frequency of the heterozygous genotype Ll. Given this, we already know that q2 = 0.16 from the question since that is how many long-tailed lizards are in the population. Now since the question is asking for the allele frequency, we need to solve for p or q. If the question was asking for genotypes, we would be solving for either p2, q2, or 2pq. So if "p" is the frequency of the dominant short tail allele and "q" is the frequency of the recessive long tail allele in the population, we can use the Hardy-Weinberg equation to calculate the allele frequency of the short tail allele (p): q2 = 0.16 Hence, q = 0.4 Use the equation p + q = 1 to find the predicted value of p. p = 1 - 0.4 = 0.6 Hence, the allele frequency for short tail is 0.60. How to Solve These Problems This question is another variation of a type of Hardy Weinberg question you may encounter on the DAT. We highly recommended that you know how to solve these types of questions for the DAT since they do show up occasionally.

E.coli producers toxin X, a deadly substance. H. pylori does not produce toxin X. In an experiment, E.coli is allowed to sit in a solution for some time. The E.coli are then removed from the solution and H. pylori are placed inside. After some time in the solution, H. pylori are now able to produce toxin X. Which of the following describes the process that allowed this to occur? A. Transduction B. Transformation C. Conjugation D. Transposable elements E. Mutation

Transformation Transformation is the process in which a bacterium takes up a piece of DNA floating in its environment. Based on the information provided within the question, the gene to produce toxin X must have been picked up by H. pylori from E. coli from its environment using the process of Transformation. transduction- virus conjugation- direct contact

Tracheids are specialized plant cells that function to: A. Photosynthesize B. Transport water C. Transport sugars D. Absorb water E. Absorb energy from the sun

Transport water A plant is made up of many different parts. The three main parts are the roots, the leaves, and the stem. A component of the plant known as xylem is located in all three parts of the plant. The structure of plant roots, leaves, and stems facilitate the transport of water and nutrients throughout the plant. The phloem and xylem are the main tissues responsible for this movement. Water potential and evapotranspiration also influence how water and nutrients are transported. Tracheids are elongated cells located in the xylem of vascular plants that serve in the transport of water and mineral salts. Another function of tracheids is providing structural support to the plant. The mature tracheids form a column of superposed, cylindrical dead cells whose end walls have been perforated, resulting in a continuous tube called a vessel or trachea.

Which organism would be most affected if it were put in a solution with an enzyme that degraded chitin? A. Yeast B. Pine tree C. Slime molds D. Diatoms E. Amoeba

Yeast Chitin is a beta-glucose polymer that functions as a structural molecule in fungal cell walls and arthropod exoskeletons. Thus, the correct answer will either belong to fungi or arthropods. Yeast falls under the category of fungi and has a cell wall that includes chitin, as shown in the image below. Therefore, if an enzyme were to degrade chitin as part of its cell wall, it would suffer the most damage.

tRNA is necessary to link together:

amino acids ranslation involves using mRNA as a template to produce a polypeptide that may fold into a protein. The ribosome holds the mRNA. The particular sequence of three nucleic acids, or codon, is "read" by the ribosome and tRNA (transfer RNA) with the corresponding amino acid, for that codon delivers the amino acid to the ribosome for polymerization into the nascent polypeptide. This process is known as translation because genetic information is translated from the language of nucleic acids to the language of amino acids and proteins. The process of translation is illustrated below. Therefore, Option B. Amino Acids, is the correct answer. CC BY 4.0 Video Solution BACK NEXT

Aerotolerant anaerobes

are bacteria with an exclusively anaerobic (fermentative) type of metabolism but they are insensitive to the presence of oxygen. They live by fermentation alone whether or not oxygen is present in their environment.

Obligate aerobes

are organisms that requires oxygen to grow. Through cellular respiration, these organisms use oxygen to metabolize substances, like sugars or fats, to obtain energy. In this type of respiration, oxygen serves as the terminal electron acceptor for the electron transport chain

Obligate anaerobes

are organisms which can only live in environments which lack oxygen. Unlike the majority of organisms in the world, these organisms are poisoned by oxygen. Obligate anaerobes are typically bacteria, and live in a variety of places naturally

Through what vessel does the liver secrete its products into the gut?

common bile duct

During embryologic development, the stage that is best described as a hollow sphere of cells is called a:

blastula Through the process of cleavage, the zygote undergoes cell division without increasing in overall size. Each new cell formed is termed as a blastomere. A ball of cells is termed a morula. After that, liquid starts to fill within the morula, pushing the middle cells outward as they continuously divide, creating a blastocoel within the middle. At this point of cleavage, a blastula is formed.The image below provides a visualization of the process of cleavage.

Statement #1: Gram-positive bacteria have a thick peptidoglycan layer instead of a capsule. Statement #2: Gram-negative bacteria stain purple due to a capsule, two membranes. A. Both statements are true B. Both statements are false C. Statement #1 is true, statement #2 is false D. Statement #1 is false, statement #2 is true

both are false The capsule is a very-organized polysaccharide layer on the outermost layer of both Gram-positive and Gram-negative bacteria. It serves to protect the bacteria against viruses, phagocytes, and detergents. Additionally, it can serve as a virulence factor, molecules that enhance their ability to cause disease.

bird forelimb and bat forelimb

homologous structures Although bird and bat wings are analogous as wings, their forelimbs are homologous as shown in the images below. Birds and bats did not inherit wings from a common ancestor with wings, but they did inherit forelimbs from a common ancestor with forelimbs. This particular example is important to know for the DAT!

The intracellular transportation of substances is primarily accomplished by _________________.

kinesin and microtubules The second type is the microtubule motor proteins: dynein and kinesin. Dynein is a motor protein that walks along microtubules towards the center of the cell (Retrograde transport). One of dynein's roles is in causing the beating of cilia and flagella. Kinesin is a motor protein that also walks along microtubules but away from the center of the cell (Anterograde transport).

The notochord is produced from which of the following layers during embryonic development?

mesoderm During gastrulation, the epiblast develops into the trilaminar embryonic disc consisting of the endoderm, mesoderm, and the ectoderm. Around Day 16 of development, a solid cylinder of cells develops under the ectoderm from mesodermal cells. This becomes the notochord and it is involved in induction, signaling the ectoderm to form the neural plate. ectoderm = neural tube

In C4 photosynthesis, the first 4-carbon intermediate that CO2 is converted to is _________ and is eventually shuttled across to _________ in the form of malate.

oxaloacetate, bundle sheath cells In C4 plants, the light-dependent reactions and the Calvin cycle are physically separated, with the light-dependent reactions occurring in the mesophyll cells (spongy tissue in the middle of the leaf), and the Calvin cycle occurring in special cells called bundle-sheath cells (found around the leaf veins). This unique leaf anatomy and biochemistry enables C4 plants to bind carbon dioxide when it enters the leaf and produce a 4-carbon compound that transfers and concentrates carbon dioxide in specific cells around the Rubisco enzyme, significantly improving the plant's photosynthetic and water use efficiency. As a result, in sunny and hot environments, C4 plants tend to be more productive than C3 plants. Examples of C4 plants include corn, millet, and switchgrass. When carbon dioxide is first input into the C4 pathway, PEP carboxylase catalyzes its transformation into oxaloacetate. Oxaloacetate is the first 4-carbon component of the C4 pathway, which is then converted into malate and shuttled to the bundle-sheath cells. Here, rubisco removes carbon dioxide into the Calvin cycle while pyruvate is recycled into PEP to repeat the process.

dominant allele freq

p

Two species of monkeys emerge from a common ancestor. They live in the same jungle and are hunted by the same predators. Both species of monkeys have evolved prehensile tails and increased upper arm strength. Despite their similarities, they are not capable of interbreeding. Which form of evolution has taken place?

parallel The form of evolution that has taken place in this scenario is parallel evolution. Parallel evolution occurs when two species from a common ancestor make similar evolutionary changes after diverging. The figure below depicts three forms of evolution. Note that divergent and parallel evolution is similar in that two species come from a common ancestor.

Two organisms are isolated in separate test tubes labelled A and B. Test tube A contains an organism that is a eukaryote capable of sexual reproduction. Test tube B contains an organism that is a prokaryote closely resembling a chloroplast. Both organisms are autotrophic. Which organism could be found in each test tube?

plant, cyanobacteria From the given option choices, only the kingdom Plantae includes multicellular eukaryotes that are characterized by photosynthetic autotrophy. Organisms that belong to this kingdom reproduce sexually using an alternation of generations scheme (alternate between distinct haploid and diploid stages

Which type of genetic material is made in the nucleolus? A. tRNA B. mRNA C. rRNA D. cDNA

rRNA The nucleolus is an organelle within the nucleus of eukaryotic cells that makes ribosomal subunits from proteins and ribosomal RNA (rRNA). It then sends the subunits out to the rest of the cell where they combine into complete ribosomes. Ribosomes make proteins; therefore, the nucleolus plays a vital role in making proteins in the cell.