MCAT Practice questions

Which of the following factors determine an enzyme's specificity? A. The 3D shape of the active site. B. The Michaelis constant. C. The type of cofactor required for the enzyme to be active. D. The prosthetic group on the enzyme.

A. -An enzyme's specificity is determined by the 3D shape of its active site. Regardless of which theory of enzyme specificity we are discussing (lock and key or induced fit), the active site determines which substrate the enzyme will react with.

When lactose hydrolyzes its substrate, lactose, which of the following occurs? A. Lactase retains it structure after the reaction. B. Lactose retains its structure after the reaction. C. Lactase increases the activation energy of the reaction. D. Lactose decreases the activation energy of the reaction.

A. -Choice (A) is correct answer because, by definition, an enzyme remains unchanged by the reaction that is catalyzes. Choice (B) is incorrect because a substrate is changed by an enzymatic reaction. Choice (C) is not true, an enzyme would decrease the activation energy. Choice (D) is also incorrect since a substrate does not affect the activation energy.

Bonding between atoms of an enzyme such as trypsin is best described as: A. peptide B. saccharide C. ionic D. van der Waals

A. -Enzymes are proteins. Proteins are composed of amino acids linked together by peptide bonds. Choice (B) - Saccharide, is a type of bond found in polysaccharides. Choice (C) - Ionic, is a chemical bond formed through electrostatic interaction between positive and negative ions. Choice (D) may be formed in secondary or tertiary structures of an enzyme but is not as good an option as (A).

Enzymes increase the rate of a reaction by: A. decreasing the activation energy. B. increasing the overall free energy of the reaction. C. both A and B. D. none of the above.

A. -Enzymes increase the rate of a reaction by decreasing the activation energy. They do not affect the overall free energy, delta G, of the reaction.

Consider the pathway: A --1-> B --2-> C --3-> D --4-> E --5-> X --6-> Y An increase in [E] leads to the inhibition of enzyme 3. All of the following are results of the process except: A. an increase in [B]. B. an increase in [Y}. C. decreased activity of enzyme 4. D. increased activity of enzyme 6.

A. -Looking at the pathway, we notice that if enzyme 3 is inhibited, everything that is controlled by it will decrease in concentration and activity. That is, the concentration of D and E will eventually decrease. The activity of enzyme 4 will also decrease, because it will be acting on a decreased amount of substrate. In addition, if enzyme 3 is inhibited, more of C will be converted to X through enzyme 5. As such, the concentration of X and Y is expected to increase, as is the activity of enzyme 6. Anything before enzyme 3 should remain unaffected. Therefore, the concentration of B will remain the same.

The many steps of glycolysis all exist in a state of dynamic equilibrium between reactant and product concentrations. Which of the following actions does NOT affect the equilibrium position of a reaction? A. Adding or subtracting heat B. Adding or removing a catalyst C. Increasing or decreasing concentrations of reactants D. Increasing or decreasing volumes of reactants

Answer: B The equilibrium of a reaction can be changed by several factors. Adding or subtracting heat, choice (A), would shift the equilibrium based on the enthalpy change of the reaction. Increasing reactant concentrations would shift the equilibrium in the direction of the product, and the opposite would occur if reactant concentrations were decreased, eliminating choice (C). Changing the volume of a reactant would affect any reaction with gaseous reactants or products, eliminating choice (D). While adding or removing a catalyst would change the reaction rate, it would not change where the equilibrium lies.

A jury member who initially feels that a strict penalty should be placed on the defendant votes for an even stricter penalty after deliberation with the other jury members. This behavior is best described by which social phenomenon? A. Social facilitation B. Group polarization C. Assimilation D. Socialization

Answer: B The fact that individual opinions became more extreme during group discussion is explained by group polarization. The jury member initially felt that a strict penalty should be given, but this opinion became more extreme after conversation with the rest of the group.

Which of the following is an example of external locus of control? A . George was late to pick up his friend Sarah, and upon arriving to her place, he was apologetic and blamed himself for losing track of time. B . Alex does poorly on this history exam and blames the clock on the wall for being too loud and not allowing him to concentrate. C. Gretchen is no longer kept awake by her roommate's late night keyboard typing. D. Lauren is talking on the phone and parks her car in her driveway, accidentally leaving the headlights on. In the morning, she blames herself for not paying attention

Answer: B The locus of control describes where individuals place blame or praise based on events that affect them. An external locus of control tends to place blame (or praise) on other people or factors, while an internal locus of control tends to place blame (or praise) on oneself. (B) is the only answer option where the blame is placed on a factor which is external to the person

Which of the following is FALSE regarding DNA replication? A . DNA replication requires an RNA primer. B . Nucleoside triphosphates are added to the 3' end. C .Bacteria require telomerase to complete their DNA strand synthesis. D . Helicase is required prior to DNA synthesis

Answer: C Due to their nonlinear nature, bacterial chromosomes do not face the same issues as eukaryotic chromosomes during DNA replication. With linear eukaryotic chromosomes, the ends of chromosomes need consistent elongation in order to prevent the successive shortening of their ends. The enzyme telomerase addresses this issue by providing a template and enzyme to lengthen the linear end with each cycle of DNA replication.

Which of the following best explains why glutamic acid is less soluble than glycine in water at a neutral pH? Please click on the correct answer: A. Glutamic acid is more acidic. B. Glutamic acid does not dissociate in water. C. Glutamic acid is larger and more hydrophobic than glycine. D. Glutamic acid has more nitrogen atoms.

Answer: C Glutamic acid is only slightly soluble in water in large part due to its hydrophobic tail acidic group at the end. Although the acidic group is present, it is not strongly acidic and the hydrophobic nature of the tail outweighs any enhanced solubility effect otherwise afforded by a carboxylic acid. Thus the correct answer is (C). (B) is incorrect because some dissociation does occur. (D) is incorrect because it is untrue and the presence of nitrogen atoms does not directly impact solubility.

Hydrocarbons with various bond orders make up biological membranes; fewer double bonds allows for tighter interactions between neighboring hydrocarbons. In which pair of hydrocarbons does each compound contain only one double bond per molecule? A. C4H10 and C2H8 B. C2H6 and C2H8 C. C4H8 and C2H4 D. C2H2 and C4H4

Answer: C Hydrocarbons with one double bond are alkenes, general formula CnH2n; they have twice as many hydrogen atoms as carbon atoms. Choice (C) is the only pair with both hydrocarbons having twice as many hydrogen atoms as carbon atoms.

The photoelectric effect, caused when some photons and electrons collide, helps radiologists distinguish tissue types. An electron in a metal object is struck by a photon whose energy is exactly equal to the metal's work function. The electron will: A. be ejected from the atom and will move faster than its previous velocity. B. be ejected from the atom and move at its previous velocity. C. be ejected from the atom and move slower than its previous velocity. D. not be ejected from the atom, but will be accelerated to a greater velocity.

Answer: C In the photoelectric effect, an electron escapes from a metal if it is struck by a photon whose energy is at least as high as the metal's work function. After it is ejected, its kinetic energy is equal to the difference between the photon's energy and the work function. Since the photon in this question has an energy that is equal to the work function, the electron's kinetic energy after ejection will be equal to zero. This means that the energy of the photon is just enough to let the electron escape; afterward, its velocity will be approximately zero, making choice (C) the correct answer.

An elevator is descending down an elevator shaft with constant speed. The elevator is supported by a single cable. Assuming the only forces at play are the tension in the cable and the force of gravity, then: A. the magnitude of the work done by the tension force is larger than the magnitude of the work done by gravity. B. the magnitude of the work done by the tension force is smaller than the magnitude of the work done by gravity. C. the net work done by the two forces is zero. D. the work done by the tension force is zero.

Answer: C In this simple system, the fact that the elevator is descending at a constant speed means the net work done by the two forces is zero. There is a magnitude for the work done by the tension in the cable (in the positive y-direction), and this eliminates (D). There is also a magnitude for the work done by gravity (in the negative y-direction). Due to the constant speed and equilibrium of the system presented, (A) and (B) can be eliminated.

Mitochondrial DNA is: circular. self-replicating. single-stranded. A. I only B. II only C. I and II only D. I, II, and III

Answer: C Mitochondria are thought to have evolved from an anaerobic prokaryote engulfing an aerobic prokaryote and establishing a symbiotic relationship; therefore, mitochondrial DNA, or mDNA, is likely to be similar to bacterial DNA. Both mDNA and bacterial DNA are organized into a single circular chromosome of double-stranded DNA that can replicate during binary fission. Therefore, Statements I and II are correct, while Statement III is incorrect

Primary groups differ from secondary groups in that: A. primary groups are shorter-lived than secondary groups. B. primary groups are larger than secondary groups. C. primary groups are formed of stronger bonds than secondary groups. D. primary groups are assigned while secondary groups are chosen.

Answer: C Primary groups have direct and close bonds between members, providing warm, personal, and intimate relationships to its members. Secondary groups, in contrast, form superficial bonds and tend to last for a shorter period of time.

In Alzheimer's disease, a protein called the amyloid precursor protein (APP) is cleaved to form a protein called β-amyloid. This protein has a β-pleated sheet structure and precipitates to form plaques in the brain. This mechanism of disease is most similar to which of the following pathogens? A. Bacteria B. Viruses C. Prions D. Viroids

Answer: C Prions are infectious proteins that cause misfolding of other proteins. Primarily, prions cause a shift toward β-pleated sheet confirmations, which leads to decreased solubility and degradability of proteins, ultimately leading to disease. This mechanism is very similar to the one described here for Alzheimer's disease, making choice (C) the correct answer.

Studying why a nod means "yes" in many cultures is most representative of which of the following sociological concepts? A. Demographic transition B. Conflict theory C. Symbolic interactionism D. Demographic shift

Answer: C Symbolic interactionism studies how individuals interact through a shared understanding of words, gestures, and other symbols. A nod is thus a symbol in many cultures that signifies "yes."

Glen brings cookies to work. Although you have not yet tasted them, you say to another coworker, "Glen is such a great guy; I'm sure these cookies are fantastic!" What type of bias is this? A. Reliance on central traits B. Direct benefits C. Halo effect D. Similarity

Answer: C The halo effect is a cognitive bias in which judgments of an individual's character can be affected by the overall impression of the individual.

Which of the following is NOT a difference that would allow one to distinguish a prokaryotic and a eukaryotic cell? A. Ribosomal subunit weight B. Presence of a nucleus C. Presence of a membrane on the outside surface of the cell D. Presence of membrane-bound organelles

Answer: C The main differences between prokaryotes and eukaryotes include: prokaryotes do not have a nucleus, while eukaryotes do, eliminating choice (B); prokaryotes have ribosomal subunits of 30S and 50S, while eukaryotes have ribosomal subunits of 40S and 60S, eliminating choice (A); and prokaryotes do not have membrane-bound organelles, whereas eukaryotes do, eliminating choice (D). The presence of a membrane on the outer surface of the cell could not distinguish a prokaryotic cell from a eukaryotic one because both gram-negative bacteria and animal cells share this feature. Thus, choice (C) is the correct answer.

A nine-year-old girl is brought to the pediatrician. Her parents describe that any time she is startled, she appears to collapse and fall asleep. She also complains of waking up in the morning unable to move. Which sleep disorder should be suspected? A. Insomnia B. Sleep deprivation C. Narcolepsy D. Sleep apnea

Answer: C The patient and her parents are describing cataplexy (a sudden loss of muscle tone and intrusion of REM sleep during waking hours, usually in response to a startling or emotional trigger) and sleep paralysis (an inability to move despite being awake, usually when waking up in the morning). These symptoms are highly suggestive of narcolepsy; in fact, some consider cataplexy to be pathognomonic for (absolutely indicative of) the disorder.

Which of the following is NOT a function of the smooth endoplasmic reticulum? A. Lipid synthesis B. Poison detoxification C. Protein synthesis D. Transport of proteins

Answer: C The smooth endoplasmic reticulum is involved in the transport of materials throughout the cell, in lipid synthesis, and in the detoxification of drugs and poisons. Proteins from the rough ER can cross into the smooth ER, where they are secreted into cytoplasmic vesicles and transported to the Golgi apparatus. Thus, from the given choices, protein synthesis is not a function of the smooth ER, but rather of the free ribosomes or the ribosomes associated with the rough ER. Choice (C) is therefore the correct answer.

A woman notices that her father has started to move his fingers in such a way that it looks like he is rolling something, despite nothing actually being there. She also notes slowed movement and a shuffling gait. Which neurotransmitter is likely to be present in decreased levels in her father's brain? A. Epinephrine B. Histamine C. Dopamine D. Serotonin

Answer: C The symptoms indicate that the woman's father likely has Parkinson's disease. This disease is caused by decreased dopamine production in the substantia nigra

Your neighbor asks you to check his mail while he is out of town, and you agree. Later that day, he asks you to water his plants as well. What technique for compliance is he using in this scenario? A. Lowball technique B. That's-not-all technique C. Foot-in-the-door technique D. Door-in-the-face technique

Answer: C This is a prime example of the foot-in-the-door technique. The neighbor first asks for a small favor and, after receiving commitment, asks for a larger favor.

Which of the following does NOT contain tubulin? A. Cilia B. Flagella C. Microfilaments D. Centrioles

Answer: C Tubulin is the primary protein in microtubules, which are responsible for the structure and movement of cilia and flagella, eliminating choices (A) and (B). Centrioles organize microtubules in the mitotic spindle, eliminating choice (D). Microfilaments are not composed of tubulin, but rather actin, making choice (C) the correct answer.

Herpes simplex virus (HSV) enters the human body and remains dormant in the nervous system until it produces an outbreak after exposure to heat, radiation, or other stimuli. Which of the following statements correctly describes HSV? A. While it remains dormant in the nervous system, the virus is in its lytic cycle. B. During an outbreak, the virus is in the lysogenic cycle. C. Herpes simplex virus integrates itself into the DNA of the cell. D. The herpes simplex virus contains a tail sheath and tail fibers.

Answer: C Viruses can exist in either the lytic or lysogenic cycle; they may even switch between them throughout their lifetime. During the lytic cycle, the virus's DNA takes control of the host cell's genetic machinery, manufacturing numerous progeny. In the end, the host cell bursts (lyses) and releases new virions, each capable of infecting other cells. In the lysogenic cycle, viral DNA is integrated into the host cell's genome, where it can remain dormant for days or years. Either spontaneously or as a result of environmental circumstances, the provirus can reemerge and enter a lytic cycle. Thus, choices (A) and (B) are incorrect because they reverse which part of the cycle the virus is in. Choice (D) describes features of bacteriophages, which are viruses that infect bacteria—not the human nervous system. Choice (C) accurately describes how HSV operates during the lysogenic cycle, making it the correct answer.

The behavior of the individuals in the Stanford prison experiment is best explained by which of the following terms? I. Bystander effect II. Deindividuation III. Internalization IV. Social loafing A. I only B. III only C. II and III only D. II and IV only

Answer: C When fulfilling particular roles, an individual's behavior can be very out of character. The changing of one's behavior (and internal ideas) to match a group is called internalization conformity. This was a key part of the experiment. The experiment also involved deindividuation, the loss of self-identity in the group setting that can lead to violent behavior.

Prior to vaccinations for poliomyelitis, widespread polio infection created wards of patients at risk of death due to loss of control of respiratory muscles. In 1928, Drinker and Shaw invented the first "iron lung," a device that sealed the patient's body from the neck down in a chamber with controllable pressure. The pressure change in the "iron lung" aided respiration by: a) increasing the positive pressure in the lungs, driving diffusion of O2. b) increasing the positive pressure in the lungs, thereby increasing lung ATP utilization efficiency. c) increasing negative pressure within the iron lung caused the patient's lungs to expand. d) delivering positive abdominal pressure driving the diaphragm.

Answer: C a) increasing the positive pressure in the lungs, driving diffusion of O2, incorrect, The patient's head and neck were outside the chamber of the "iron lung", therefore the air pressure in the lungs was unaffected. b) increasing the positive pressure in the lungs, thereby increasing lung ATP utilization efficiency, incorrect, See choice "a", and pressure does not affect ATP utilization. c) negative pressure within the "iron lung" causing the patient's lungs to expand, correct. d) positive abdominal pressure driving the diaphragm, incorrect, Although the diaphragm is involved in normal respiration, the "iron lung" works by mimicking the function of the intercostal muscles which expand the thoracic cavity, thereby increasing lung volume to pull in air. "Driving the diaphragm", and "positive abdominal pressure", are not part of the "iron lung" mechanism.

Hemolytic bacteria are those that are able to destroy red blood cells. A sample of blood is added to a plate of bacteria. After 48 hours, the extracellular concentration of mitochondria is observed to have increased. This finding is most consistent with which of the following statements? A. The bacteria were hemolytic, destroying red blood cells during those 48 hours. B. The bacteria were non-hemolytic, and some of them lysed during those 48 hours. C. The plate contained more than one type of bacteria. D. The plate contained more than one type of human cell.

Answer: D

What stage of protein synthesis does NOT require energy? A. Initiation B. Elongation C. Termination D. All stages of protein synthesis require energy

Answer: D

Conductive deafness is often caused by accumulated fluid in the middle ear inhibiting the passage of sounds to the cochlea and auditory nerve. Sensori-neural deafness is caused by damage to, or malformation of, the inner ear or auditory nerve. Which of the following are true concerning sound waves? I. Sound waves can be propagated through a vacuum. II. Sound waves travel fastest through a gas. III. Sound waves are transverse waves. A. I only B. I and III only C. II and III only D. None of the above

Answer: D I. Sound waves are mechanical disturbances that are propagated through deformable material mediums. II. Sound waves travel faster through solids than liquids. Sound waves travel faster through liquids than gases. III. Sound waves are longitudinal waves.

A person suffering from severe dehydration and starvation would NOT be expected to have elevated plasma concentrations for which of the following hormones? A) ADH B) Cortisol C) Aldosterone D) Insulin

Answer: D ADH and aldosterone both increase blood pressure so they would be expected to appear in high plasma concentrations in response to the low blood pressure, eliminating choices A and C. Cortisol would be expected in high plasma to increase carbohydrate, protein, and fat availability, making B false. That leaves answer choice D. Insulin lowers blood glucose levels, which is expected to appear in the blood after a sugary meal. In the case of starvation, the body would respond by increasing blood glucose levels via the production of glucagon.

Amino acids are characterized by two highly versatile functional groups. Which of the following is NOT a reaction that amino acids can undergo due to these functional groups? A. Nucleophilic addition B. Esterification C. Amide bond formation D. Keto-enol tautomerism

Answer: D Amino acids have both a primary carboxyl group and amine group. Due to these two groups, there are a variety of reactions possible. (A) and (C) are possible, which would involve the amino acid's amine group. Lastly, (B) is possible, which would involve the amino acid's carboxylic acid group.

Which of the following types of nucleic acid could form the genome of a virus? I. Single-stranded RNA II. Double-stranded DNA III. Single-stranded DNA A. I only B. II only C. I and II only D. I, II, and III

Answer: D In a virus, the nucleic acid can be either DNA or RNA and—in both cases—can be either single- or double-stranded. Therefore, all of the types of nucleic acids listed here could be used for a viral genome, making choice (D) the correct answer.

In a closed system with constant temperature, pressure can be plotted against volume in a PV diagram. Given this, which of the following is NOT true? A. The amount of energy expended by the system can be estimated by an area on the graph. B. The relationship between pressure and volume would always be linearly decreasing. C. The change in internal energy is equal to 0. D. An appropriate example that can be plotted in this PV diagram is an ideal gas in a container (in a constant-temperature environment) which is allowed to expand slowly.

Answer: B A) is eliminated because the amount of energy expended (or received) by the system is work done that can be estimated by an area under the curve, as shown in the PV diagram below. (B) is correct because this relationship is not linearly decreasing, and is instead hyperbolic. (C) is eliminated because in an isothermal process (constant temperature), the internal energy is dependent on temperature. So, with temperature constant, the change in internal energy is equal to 0. Lastly, (D) is eliminated, because the example mentioned is a clear example of a process that can be plotted in a PV diagram

Which of the following is true regarding bipolar disorders? I. They have little, if any, genetic heritability. II. They are associated with increased levels of serotonin in the brain. III. They all require at least one depressive episode for diagnosis. A. I only B. II only C. I and III only D. II and III only

Answer: B Bipolar disorders have been shown to be highly heritable and are associated with increased levels of norepinephrine and serotonin in the brain. Bipolar I disorder can be diagnosed with a single manic episode and does not require a major depressive episode. Bipolar II disorder requires at least one hypomanic episode and one major depressive episode. Cyclothymic disorder contains at least one hypomanic episode and dysthymia.

Elephant seal males mate with multiple females each mating season, while females only have one mate each. What type of mating system is this? A. Polyandry B. Polygyny C. Monogamy D. Promiscuity

Answer: B Polygamy involves a male having exclusive relationships with several females (polygyny) or a female having exclusive relationships with several males (polyandry), choice (A). Monogamy, choice (C), consists of exclusive mating relationships. Promiscuity, choice (D), refers to a member of one sex mating with any member of the opposite sex

A particular template DNA strand (noncoding strand) is composed of 18% cytosine and 20% guanine. What percentage of its RNA transcript will contain cytosine assuming no introns are removed? Please click on the correct answer: A 18% B 20% C 36% D 38%

Answer: B Since cytosine is present in both DNA and RNA, it should be present in the RNA transcript. From the template strand, all G nucleotides would be transcribed into C. Thus the way to determine the amount of C in the RNA transcript is to look at the amount of G that is in the template strand which was 20%. Thus (B) is the correct answer.

Hardy-Weinberg equilibrium refers to a population in which gene frequencies are not changing and the gene pool remains in a stable state. Which of the following conditions is necessary for this to occur? A. Small populations, because there are fewer individuals and thus, less genetic diversity B. Genes in a population that all confer roughly the same reproductive advantage C. Large amount of migration between several populations, ensuring that selection remains random D. Individuals with certain traits who mate more, thus keeping these traits in equilibrium

Answer: B Small populations, choice (A), are less likely to remain in Hardy-Weinberg equilibrium because they are more susceptible to random variations in allele frequencies, or genetic drift. Migration, choice (C), means that the gene pool is not in a stable state. The different populations could, for instance, be under slightly different selective pressures, and migration between populations would prevent equilibrium. If increased mating were associated with specific traits, choice (D), that would confer a reproductive advantage on those traits, thus changing the gene frequency. Only choice (B) is correct: when all genes in a population offer the same reproductive advantage, no gene will be favored by natural selection and frequencies will remain constant.

Which of the following activities occurs in the Golgi apparatus? A. Synthesis of proteins B. Modification and distribution of proteins C. Breakdown of lipids and carbohydrates D. Production of ATP

Answer: B The Golgi apparatus consists of a stack of membrane-enclosed sacs. It receives vesicles and their contents from the endoplasmic reticulum, modifies them (through glycosylation, phosphorylation, and other mechanisms), repackages them into vesicles, and distributes them to appropriate locations in the cell. Protein synthesis occurs in ribosomes and rough endoplasmic reticulum, eliminating choice (A). Lipid and carbohydrate breakdown takes place in the peroxisomes and cytoplasm, eliminating choice (C). ATP production occurs in the mitochondria, eliminating choice (D).

A Cuban-American man living in the United States has the dominant physical features of a black man. He speaks Spanish, prefers Latin foods, and listens to Latin music. His preferences are best defined through which of the following attributes? I. Race II. Ethnicity III. Culture A. I only B. II only C. II and III only D. I, II, and III

Answer C Although one's dominant physical features are associated with race, this man's preferences are those of Latino ethnicity and culture. Ethnicity is a social construct that considers language, religion, nationality, and cultural factors. Culture relates to a group's way of life; the preferences listed in the question are examples of material and symbolic culture.

At what point does crossing over of non sister chromatids occur? A. During prophase of meiosis B. During prophase of mitosis C. During anaphase II of meiosis D. None of the above

Answer: A

A bacterial cell is noted to be resistant to penicillin. The bacterium is transferred to a colony that lacks the fertility factor, and the rest of the colony does not become resistant to penicillin. However, the penicillin-resistant cell has also started to exhibit other phenotypic characteristics, including secretion of a novel protein. Which of the following methods of bacterial recombination is NOT likely to account for this change? A. Conjugation B. Transformation C. Transduction D. Infection with a bacteriophage

Answer: A A bacterial cell that does not rapidly cause a phenotypic change in the rest of the colony is likely not F+, meaning that this cell is not able to form a sex pilus for conjugation. The expression of new phenotypic characteristics indicate that this bacterium may have acquired some quantity of genetic information, which can be acquired by either transformation, choice (B), or transduction (which occurs via bacteriophage infection), choices (C) and (D)

After infection of a cell, a viral particle must transport itself to the nucleus in order to produce viral proteins. What is the likely genomic content of the virus? A. Double-stranded DNA B. Double-stranded RNA C. Positive-sense RNA D. Negative-sense RNA

Answer: A A virus that requires transport to the nucleus in order to produce viral proteins likely requires use of nuclear RNA polymerase in order to create mRNA that can be translated to protein. Only DNA viruses require this transport before any protein can be synthesized.

A researcher is testing a new molecular compound and notes that the compound is an antagonist of estrogen. If present in the body, this compound would likely: Please click on the correct answer: A. block LH production and prevent ovulation. B. inhibit the production of GnRH. C. block serotonin production. D. prevent the formation of primary oocytes

Answer: A As an antagonist to estrogen, this molecular compound would interfere with ovulation. Normal levels of estrogen usually suppress the LH surge (estrogen levels are at their highest right before the LH surge). Since an antagonist of estrogen would have a similar structure, the suppression of the LH surge would continue, and ovulation would be prevented.

Exposure to endotoxin triggers a rapid immune response without requiring past exposure. The immune response is most likely mediated by: A the innate immune system. B B cells. C T cells. D the adaptive immune system.

Answer: A B cells and T cells are both part of the adaptive immune system, both of which involve more complex responses and are generally slower in responding to novel antigens. The innate immune system is a rapid response mechanism and mediates respones without requiring previous exposure to an antigen

Which of the following organelles is surrounded by a single membrane? A. Lysosomes B. Mitochondria C. Nuclei D. Ribosomes

Answer: A Lysosomes are vesicular organelles that digest material using hydrolytic enzymes. They are surrounded by a single membrane. Both mitochondria and nuclei are surrounded by double membranes, eliminating choices (B) and (C). Ribosomes must not be surrounded by membranes because they are found not only in eukaryotes, but also in prokaryotes, which lack any membrane-bound organelles, eliminating choice (D).

How many liters of .3M HCL can be made from a 2: stock solution of 1.5M HCL? A. 10L B. 12L C. 6L D. 20L

Answer: A M1V1=M2V2 (0.3)(V1)=(1.5)(2) V1= 10

What is the main function of the nucleolus? A. Ribosomal RNA synthesis B. DNA replication C. Cell division D. Chromosome assembly

Answer: A The nucleolus (not to be confused with the nucleus in general) is a dense structure within the nucleus where ribosomal RNA (rRNA) is synthesized. Choice (A) is therefore the correct answer.

Which of the following does NOT describe connective tissue cells? A. They account for most cells in muscles, bones, and tendons. B. They secrete substances to form the extracellular matrix. C. In organs, they tend to form the stroma. D. In organs, they provide support for epithelial cells.

Answer: A While bones and tendons are composed predominantly of connective tissue cells, muscle tissue is considered a different tissue type. Other examples of connective tissue include cartilage, ligaments, adipose tissue, and blood. Connective tissue often secretes substances to form the extracellular matrix, such as collagen and elastin, eliminating choice (B). Choices (C) and (D) are essentially identical and can both be eliminated: in organs, connective tissue often forms the support structure for epithelial cells, called the stroma.

Consider a biochemical reaction A to B, which is catalyzed by A-B dehydrogenase. Which of the following statements is true? A. The reaction will proceed until the enzyme concentration decreases. B. The reaction will be more favorable at 0 degrees C. C. A component of the enzyme transferred from A to B. D. The free energy change (delta G) of the catalyzed reaction is the same as for the uncatalyzed reaction.

D. -In an enzyme-catalyzed reaction, the rate of a reaction is increased by a decrease in the activation energy. Furthermore, enzymes are not changed or consumed during the course of the reaction. Also, the overall free energy change of the reaction, delta G, remains unchanged in the presence of an enzyme.

At which pH would pancreatic enzymes work at maximum activity? A. 5.3 B. 6.7 C. 7.2 D. 8.5

D. -Pancreatic enzymes work optimally in the alkaline condition of the small intestine. It is not necessary to know the exact pH at which these enzymes work because the only very basic pH is seen in (D), which is 8.5.

Discuss why competitive inhibition can be overcome with increasing substrate concentration but non-competitive inhibition cannot be overcome.

-Competitive inhibitors are structurally similar to the substrate of an enzyme. This means that in the course of catalyzing reactions the enzyme can bind the inhibitor instead of the substrate. Imagine there are an equal number of inhibitor and substrate molecules. The chance that the enzyme will bind the inhibitor is equal to the chance that it will interact with the substrate. Thus, the rate of catalysis will be decreased, effectively inhibiting the enzyme. However, if the concentration of substrate if 1,000 or 100,000 times greater than the concentration of inhibitor, then the chance the enzyme will randomly interact with the inhibitor instead of the substrate falls dramatically (practically to zero). -Noncompetitive inhibitors do not associate with the enzyme at the active site. Instead, they bind at an allosteric site. When a noncompetitive inhibitor is bound, the enzyme cannot catalyze bind the substrate. Increasing the concentration of substrate will not decrease the likelihood of a noncompetitive inhibitor associating at an allosteric site.

Compare and contrast the the concept of allosteric effectors with non-competitive inhibition.

-First, all noncompetitive inhibitors bind at allosteric sites. The binding of noncompetitive inhibitors, however, does not affect the binding of substrate to the active site (and vice versa). What noncompetitive inhibitors do affect is the ability for the enzyme to catalyze the reaction and release product. In contrast, allosteric effectors allow the enzyme to exist in two different confirmations (T and R), in which one state binds substrate more readily than the other. Again, this is in direct contract to noncompetitive inhibitors, which do not influence the binding of substrate.

Why is negative feedback inhibition more common than positive feedback loops? Are there biological examples when positive feedback is necessary?

-Most biological conditions, such as blood pH, body temperature, and blood pressure, must be kept within a narrow range. Negative feedback allows for the maintenance of these conditions. If a homeostatic system moves too far to one extreme, negative feedback will brings the levels back within biologically acceptable conditions. Positive feedback, however, has the opposite effect. The more a process moves in a particular direction, the more positive feedback will keep it moving in that same direction. Two examples in which positive feedback is important are blood clotting and childbirth.

Which of the following statements about enzyme kinetics is false? A. An increase in the substrate concentration (at constant enzyme concentration) leads to proportional increases in the rate of the reaction. B. Most enzymes operating in the human body work best at a temperature of 37 degree C. C. An enzyme-substrate complex can either form a product or dissociate back into the enzyme and substrate. D. Maximal activity of many human enzymes occurs around pH 7.2.

A. -Most enzymes in the human body operate a maximal activity around a temperature of 37 degrees C and a pH of 7.2, which is the pH of most body fluids. In addition, as characterized by the Michaelis-Menten model, enzymes form an enzyme-substrate complex, which can either dissociate back into the enzyme and substrate or proceed to form a product. We can eliminate B, C, and D. An increase in the substrate concentration, while maintaining a constant enzyme concentration, leads to a proportional increase in the rate of the reaction only initially. However, once most of the active sites are occupied, the reaction rate levels off, regardless of further increases in substrate concentration. At high concentrations of substrate, the reaction rate approaches its maximal velocity and is no longer changed by further increases in substrate concentration. Therefore statement A is not entirely true.

Which of the following is/are function(s) of NADPH in the cell? I. Antimicrobial resistance via bacterial destruction by bleach within lysosomes. II. Involvement in the production of the precursors to steroid hormones. III. Functional carriage of energy across organelle membranes for use within the mitochondria A. I only B. I and II only C. II and III only D. I, II, and III

Answer: B NADPH has three primary functions: involvement in biosynthesis of lipids and cholesterol (the precursor to steroid hormones), production of bactericidal bleach in the lysosomes of certain white blood cells, and maintenance of a supply of reduced glutathione for protection against free radical damage. Energy carriage is an important function of NADH, not NADPH.

Which of the following scenarios best fits culture lag? Please click on the correct answer: A. A family immigrates from a country with frequent water shortages and maintains the policy of keeping the bathtub full of water at all times. B. High schools relax bans on cell phone usage several years after their use among teenagers becomes commonplace. C. A culture with no history of exposure to technology is suddenly provided with electronics which it subsequently fails to adopt. D. A group of children learns how to play a new game from children in another neighborhood. The game slowly spreads across the general population.

Answer: B Culture lag is the catch-up or lag that a culture experiences during the adoption of new technologies. Often culture lag results in tensions from forces that resist the change. The best example of this is (B), as schools' failure to recognize the changes in the ways students use technology led to bans of the technology's use. It takes a while for those same schools to relax their bans. (A) is a better example of culture shock, but is also not a good description of culture lag because it is not representative of a technological change they are adopting. (C) is incorrect because culture lag is about how the culture responds as technology is adopted and cannot happen if the technology is not adopted. (D) is incorrect as it is not relevant to culture lag.

Which of the following is the correct sequence of the development of a mature sperm cell? A. Spermatid → spermatocyte → spermatogonium → 2° spermatocyte → spermatozoan B. Spermatogonium → 1° spermatocyte → 2° spermatocyte → spermatid → spermatozoan C. Spermatozoan → 1° spermatocyte → 2° spermatocyte → spermatogonium → spermatid D. Spermatogonium → 1° spermatocyte → 2° spermatocyte → spermatozoan → spermatid

Answer: B Diploid cells called spermatogonia differentiate into primary spermatocytes, which undergo the first meiotic division to yield two haploid secondary spermatocytes. These undergo a second meiotic division to become immature spermatids. The spermatids then undergo a series of changes leading to the production of mature sperm, or spermatozoa.

Which of the following orders carbon, silicon, and fluorine based on first ionization energies? A Silicon > carbon > fluorine B Fluorine > carbon > silicon C Silicon > fluorine > carbon D Carbon > fluorine > silicon

Answer: B Electronegativity increases as you go up and to the right in the Periodic Table. Of the three listed, fluorine is the closest element to the upper-right in the Periodic Table. The first ionization energy measures the difficulty in removing a valence electron. Because of fluorine's position and inherent electronegativity, it is very difficult to remove one of its valence electrons. Thus, fluorine will have the highest first ionization energy. Since silicon is in the row below carbon, it has an added orbital of electrons, making it slightly easier to remove an outer electron. This extra orbital (compared to carbon) results in less of an overall force of attraction between the outer electrons and nucleus. Thus, silicon will have the lowest first ionization energy.

Which of the following is an example of group polarization? A. On the eve of a large group project being due, Eric does not submit his portion of the team project to the rest of his teammates until the last minute. B. After a class discussion about a certain campus-wide ban, students who are against the ban will defend their positions far more strongly than they would have beforehand on their own. C. After deliberation, a jury finds themselves split on their decision despite being closer to a consensus prior to the deliberation. D. During a team discussion, Sarah takes the role of team leader and tries to persuade the group into a consensus for the sake of everyone's time.

Answer: B Group polarization is commonly seen in group-decision making. It describes the tendency for groups to reach decision that are more extreme (positive or negative) than the original positions of the individual group members. (B) showcases an example of this, since individuals are said to hold more extreme versions of their positions after a group discussion

Which of the following trends regarding healthcare disparities has NOT been documented? A. Females are more likely to be insured than males. B. Primary care use is more likely among males than females. C. Low-income individuals have more difficulty accessing care than high-income individuals. D. LGBT individuals have more barriers to healthcare than heterosexuals.

Answer: B In comparison to females, males visit primary care doctors less frequently. All of the other trends listed here have been documented

Which of the following is TRUE regarding unfertilized oocytes in human females? A. Unfertilized oocytes mature in the uterus B. Unfertilized oocytes mature in response to an increase in FSH and LH C. Unfertilized oocytes mature in response to an increase in gonadotropin releasing hormone (GnRH) D. Unfertilized oocytes mature in response to an increase in estrogen

Answer: B In human females, FSH stimulates the growth of a follicle and LH stimulates the production of estrogen. Once the follicle is mature, it ruptures and then releases the oocyte. The remaining cells in the follicle then develop into the corpus luteum.

Excitatory estrogen receptors have been recently found on osteoblasts. During menopause, there is a sharp decrease in the amount of estrogen production. Which of the following can be expected? A. A decrease in the ratio of osteoclast/osteoblast activity, which may lead to osteoporosis B. An increase in the ratio of osteoclast/osteoblast activity, which may lead to osteoporosis C. A decrease in the ratio of osteoclast/osteoblast activity, which may prevent osteoporosis D. An increase in the ratio of osteoclast/osteoblast activity, which may prevent osteoporosis

Answer: B In menopause, there is a decrease in the concentration of estrogen. Hence, there will be decreased stimulation of the osteoblasts. Since osteoblasts and osteoclasts are in constant opposition, decreased stimulation of the osteoblasts will result in an increased ratio of osteoclast to osteoblast activity. This will lead to decreased bone formation and increased bone resorption, which may lead to osteoporosis. The correct answer is (B).

Prolonged vitamin B12 deficiency can be associated with subacute combined degeneration of the spinal cord. Patients with this disease have difficulty walking because they lose the ability to feel where their feet are in space. This represents a loss of: A. vestibular sense. B. kinesthetic sense. C. parallel processing. D. feature detection.

Answer: B Kinesthetic sense, or proprioception, refers to the ability to tell where body parts are in three-dimensional space. The sensors for proprioception are found predominantly in the muscles and joints. Loss of vestibular sense, choice (A), would also cause difficulty walking, but this would be due to a sense of dizziness or vertigo, not an inability to feel one's feet.

In the ZW sex-determination system for birds, males (ZZ) are the homogametic sex while females (ZW) are the heterogametic sex. What is the most likely regulatory mechanism for the potential imbalance in gene expression between male and female birds? A) Post-transcriptional modification of half the male sex chromosomes gene products B) Inactivation of one Z chromosome in males C) Inactivation of the W chromosome in females D) Destruction of one Z chromosome in males

Answer: B This question asks us to apply knowledge of sex chromosome inactivation in humans to an analogous situation in birds. Opposite to male birds (ZZ), mammalian males (XY) are heterogametic and carry one X and one Y chromosome. Similarly, female birds (ZW) are heterogametic while mammalian females (XX) are homogametic. In the mammalian XY sex-determination system, females randomly inactivate one of their X chromosomes to prevent a redundancy in gene products (i.e. mRNA and proteins). These inactivated chromosomes are known as Barr bodies. In the case of bird species, the homogametic males (ZZ) must inactivate one of their Z chromosomes to achieve the appropriate reduction in gene products. Therefore, the correct answer is B.

In which of the following structures of a healthy human male would immotile sperm incapable of fertilization be found? Vas deferens Seminiferous tubules Urethra A) I only B) II only C) I and II D) I, II, and III

Answer: B This question is testing your understanding of sperm development within the male reproductive system. To answer this question, you must know the pathway sperm travels from the testes to ejaculation: seminiferous tubules -> epididymis -> vas deferens -> ejaculatory duct -> urethra -> penis. Furthermore, you must also know that the epididymis is the location where spermatozoa gain motility and fertilization capabilities. Therefore, immotile sperm that are incapable of fertilization may be found in the parts of the male reproductive system preceding the epididymis. Therefore, only II is correct making B the correct answer.

Some people with anxiety disorders respond to stress by hyperventilating. It is recommended that these people breathe into a paper bag and then re-breathe this air. Why is this treatment appropriate? A. Hyperventilation causes an increase in blood carbon dioxide, and breathing the air in the bag helps to readjust blood levels of carbon dioxide. B. Hyperventilation causes a decrease in blood carbon dioxide, and breathing the air in the bag helps to readjust blood levels of carbon dioxide. C. Hyperventilation causes an increase in blood oxygen, and breathing the air in the bag helps to readjust blood levels of oxygen. D. Hyperventilation causes a decrease in blood oxygen, and breathing the air in the bag helps to readjust blood levels of oxygen.

Answer: B When people hyperventilate, their respiratory rate increases. When the respiratory rate increases, more carbon dioxide is blown off. This causes a shift to the left in the bicarbonate buffer equation, and the blood becomes more alkaline. Breathing into the bag allows some of this carbon dioxide to be returned to the bloodstream in order to maintain the proper pH.

The production of ATP via cellular respiration is governed by the following balanced reaction: C6H12O6 + 9 O2 à 6 CO2 + 6 H2O + ATP If there are 360 grams of C6H12O6 (MW = 180 g/mole) in the reaction vessel initially and 440 grams of CO2 are produced, what is the limiting reagent? A. C6H12O6 B. O2 C. CO2 D. H2O

Answer: B you must calculate the theoretical amount of CO2 that is produced given 360 grams of C6H12O6. If all 360 grams (2 moles) of glucose initially present reacts, then 528 g (12 moles) of CO2 should theoretically be produced. 360 g C6H12O6 x (1 mol C6H12O6 / 180 g C6H12O6) x (6 mol CO2 / 1 mol C6H12O6) x (44 g CO2 / 1 mol CO2) = 528 g CO2 Since only 440 grams of carbon dioxide are actually produced, not all of the glucose combusts. Thus, the oxygen must be the limiting reagent in this problem making answer choice B correct. Choices C and D can be eliminated because products are never limiting reagents. Since there will be leftover C6H12O6, it is not the limiting reagent, eliminating answer choice A

An infectious agent is probably a virus instead of a bacterium if it: a) lacks membrane-bound organelles b) cannot reproduce in acellular culture c) has a length of 1?m, about the size of a mitochondrion d) contains DNA

Answer: B Viruses possess DNA or RNA but not both, require a host cell's reproductive machinery in order to reproduce, and have a size 10-100nm. For the MCAT: eukaryotic cell > bacterium (roughly size of mitochondrion) > virion (roughly size of protein, roughly 100x smaller than bacterium, 1000x smaller than eukaryotic cell, cannot be seen with optical microscope). a) lacks membrane-bound organelles, incorrect, Both viruses and bacteria lack membrane-bound organelles. b) cannot reproduce in acellular culture, correct. Viruses require host cells in order to reproduce. c) has a length of 1μm, about the size of a mitochondrion, incorrect, This is the size of a bacterium. d) contains DNA, incorrect, Both bacteria and viruses may contain DNA.

In rural communities, a small economy exists between landowners through the trade of corn. Multiple families own fertile land to grow corn and make money, but some families do not have the same quality of fertile land. Families lacking fertile land have invented a stacking system that allows their corn stalks to grow higher than normal, increasing their yield per square meter. Which type of economy most closely aligns with this? A. Socialism B. Feudalism C. Capitalism D. Mixed economy

Answer: C

Which of the following is NOT true regarding lymphatic cells and their function(s)? Please click on the correct answer: A . Neutrophils are phagocytic cells. B. Eosinophils secrete enzymes that fight against parasites. C. Basophils secrete the antidiuretic hormone to aid in vasodilation. D. B cells secrete antibodies.

Answer: C Basophils secrete histamine, not ADH, as one of its functions to fight off pathogens. In doing so, the histamine increases the permeability of the capillaries to white blood cells (as well as some proteins), and this allows for the white blood cells to interact with pathogens present in infected tissues.

Which of the following is true with regard to a major depressive episode? A. It may last less than two weeks. B. It must involve thoughts of suicide or a suicide attempt. C. It may involve a decrease in sleep. D. It must involve feelings of sadness.

Answer: C Depression is marked by a period of at least two weeks in which the patient has five of nine cardinal symptoms, one of which must be depressed mood or lack of interest (anhedonia). While decreased need for sleep is commonly seen in manic episodes, it may also appear in depression as sleep disturbance is one of the nine cardinal symptoms. Not all depressed individuals are suicidal, as in choice (B). In older men, depression may often manifest as anhedonia without feelings of sadness, invalidating choice (D).

A contentious issue in stem cell biology is whether mesenchymal stem cells differentiate into cartilage, bone, and fat tissue in vivo or if those effects are only seen in vitro. How might researchers design an experiment to confirm in vivo differentiation? Please click on the correct answer: A. Inject a mouse with labeled mesenchymal stem cells that have been cultured in vitro and track the label at common sites of differentiation. B. Treat mice with a drug that targets mesenchymal stem cells and measure the production of bone, cartilage, and fat tissues. C. Mutate a line of mice to produce a label on their mesenchymal stem cells, and track the activity of the cells at common sites of differentiation. D. Track the population of mesenchymal stem cells in mice as they age and begin to produce less bone, cartilage, and fat tissue.

Answer: C Experimental design does not always require in-depth knowledge of the contents of the experiment. Since the assertion is that differentiation may only be occurring in vitro, the use of cells that have been cultured in vitro should be avoided, even if they are being injected back into a mouse. The reason is that the cell culture conditions could alter the cell population in some way that would not happen in vivo and would thus affect the results. For this reason, (A) can be eliminated. (B) can be eliminated because there is no indication that these tissues are only produced by the mesenchymal stem cells, just that the stem cells can differentiate into those tissues. Thus if no effect is observed when the drug is administered, it could simply be the case that other cell types take over for the lack of mesenchymal stem cells. (D) can be eliminated because many other factors contribute to aging and these confounding factors would be difficult to track against the population of mesenchymal stem cells. (C) is the correct answers because it is the closes approximation to in vivo conditions with minimal manipulation of the cell conditions while still allowing direct observation of their activities in the body.

Which of the following is FALSE regarding the fight-or-flight response? A. The fight-or-flight response can be described as being part of the sympathetic nervous system. B. The fight-or-flight response can cause a person to feel emotion. C. The fight-or-flight response involves the release of antidiuretic hormone (ADH). D. The fight-or-flight response can suppress the immune system.

Answer: C (A) is eliminated because the fight-or-flight response is classically defined as being under control of the autonomic nervous system, which is divided into the sympathetic and parasympathetic nervous system. (B) is eliminated because the response does cause a person to feel emotion (e.g. fear, excitement). (D) is eliminated because the reaction of the response can cause the release adrenaline and cortisol, the latter which can increase suppression of the immune system. (C) is correct because ADH is not released during this response, but adrenocorticotropic hormone (ACTH) can be.

A compound consists of approximately 72g carbon and 6g hydrogen. What is the empirical formula? a) C6H6 b) CHO c) CH d) C6H12

Answer: C A is incorrect because its the molecular formula not the empirical formula. Convert grams into moles and then change ratio to smallest possible to solve this equation.

Antidiuretic hormone (ADH) is a peptide hormone produced in the hypothalamus and released by the posterior pituitary gland in response to an increase in serum osmolarity. Diabetes insipidus is a disease characterized by a physical or functional lack of ADH and production of dilute urine. Given the symptoms of diabetes insipidus, one would expect ADH to act on: A. Na/K/Cl channels in the loop of Henle. B. NaCl channels in the distal convoluted tubule. C. H2O channels in the distal convoluted tubule and collecting duct. D. Na/H channels in the proximal tubule.

Answer: C ADH acts to concentrate urine by encouraging reabsorption of water in the distal convoluted tubule and collecting duct of the nephron. It has no effect on any of the other channels in choices (A), (B), and (D).

Which of the following is TRUE regarding self-actualization as argued by a humanistic psychologist? Please click on the correct answer: A. Self-actualization is associated with peak experiences B. Self-actualization is associated with extroversion C. Self-actualization is innate D. Self-actualization is a task confined to adolescence

Answer: C Abraham Maslow largely contributed to the basis of humanistic psychology. And as just one of the methods in psychology used for studying and understanding personality, the humanistic approach to personality places self-actualization at the top of Maslow's hierarchy of needs; moreover, becoming "fully human" is something innate to everyone.

Which of the following is NOT an example of some form of social mobility? A. Paul is moving into a new apartment and changes jobs as a barista from one coffee shop to another. B. Lauren starts off at an entry-level position at an accounting firm and moves up to senior VP level within 20 years. C. Stacey, a veteran TV writer, receives a 5% bonus compensation based on her salary. D. George is a first-generation college student with immigrant parents who worked hard labor jobs throughout their lives.

Answer: C All of the above are forms of social mobility, except for (C). (A) is a form of horizontal mobility, which means the mobility due to changing positions within the same social level. (B) is a form of intragenerational mobility, which means moving up (or down) the social ladder within a person's lifetime. Lastly, (D) is a form of intergenerational mobility, which is characterized by the change from one generation to the next.

According to Erikson's stages of psychosocial development, which of the following would be the most important for a recent college graduate to accomplish? A. Figuring out what identities are most important to him or her B. Feeling like a contributing member of society C. Forming an intimate relationship with a significant other D. Finding a feeling of accomplishment in his or her life

Answer: C As a postadolescent young adult, this person would be be described by Erikson as experiencing the conflict of intimacy vs. isolation, and so forming significant relationships with others would be a primary goal. Choices (B) and (D) represent the next two stages in life (generativity vs. stagnation and integrity vs. despair, respectively), while choice (A) is the conflict that Erikson would say should have been resolved in adolescence (identity vs. role confusion).

Resistance to antibiotics is a well-recognized medical problem. Which mechanism(s) can account for a bacterium's ability to increase its genetic variability and thus adapt itself to different antibiotics? Binary fission Conjugation Transduction A. I and II only B. I and III only C. II and III only D. I, II, and III

Answer: C Bacterial cells reproduce by binary fission, an asexual process in which the progeny is identical to the parent. Therefore, Statement I does not increase genetic variability. Conjugation can be described as a sexual mating in bacteria; it is the transfer of genetic material between two bacteria that are temporarily joined. Transduction occurs when fragments of the bacterial chromosome accidentally become packaged into viral progeny produced during a viral infection and can subsequently be introduced into another bacterium by the viral vector. Therefore, both Statements II and III increase bacterial genetic variability.

After a brief period of intense exercise, the activity of muscle pyruvate dehydrogenase is greatly increased. This increased activity is most likely due to: A. decreased ADP. B. increased acetyl-CoA. C. increased NADH/NAD+ ratio. D. increased pyruvate concentration.

Answer: D In most biochemical pathways, only a few enzymatic reactions are under regulatory control. These often occur either at the beginning of pathways or at pathway branch points. The pyruvate dehydrogenase (PDH) complex controls the link between glycolysis and the citric acid cycle, and decarboxylates pyruvate (the end product of glycolysis) with production of NADH and acetyl-CoA (the substrate for the citric acid cycle). After intense exercise, one would expect PDH to be highly active to generate ATP. ADP levels (choice (A)) should be high because ATP was just burned by the muscle. Acetyl-CoA (choice (B)) is an inhibitor of PDH, causing a shift of pyruvate into the gluconeogenesis pathway. A high NADH/NAD+ ratio (choice (C)) would imply that the cell is already energetically satisfied and not in need of energy, which would not be expected in intensely exercising muscle.

Hyperbaric oxygen may be used as a treatment for certain types of bacterial infections. In this therapy, the patient is placed in a chamber in which the partial pressure of oxygen is significantly increased, increasing the partial pressure of oxygen in the patient's tissues. This treatment is most likely used for infections with: A. obligate aerobic bacteria. B. facultative anaerobic bacteria. C. aerotolerant anaerobic bacteria. D. obligate anaerobic bacteria.

Answer: D Obligate anaerobes cannot survive in the presence of oxygen and would likely be killed by such a therapy, treating the infection. The other types of bacteria listed can all survive in the presence of oxygen and would likely not be treated using this therapy.

Astronauts experience health conditions caused by living in a low-gravity (or zero-gravity) environment. Muscles atrophy and blood volume decreases. Satellite A is resting on the surface of the Earth, while satellite B is orbiting the Earth at an altitude of Re (equal to the radius of the Earth), directly over Satellite A. If B is twice as massive as A, what is the ratio of Earth's gravitational force on A to Earth's gravitational force on B? A. 1/4 B. 1/2 C. 1 D. 2

Answer: D The force of gravity between two bodies given by: F=GM1M2/ r squared Therefore, the force of Earth on A (FAe) to Force of Earth on B (FBe) is given by: (A) This implies that the force will be greater on Satellite B, which is not true. (B) Ignoring the altitude difference brings you to this choice. (C) Neglecting to square the denominator leads you to this choice

Which of the following brain stem areas is most important in controlling breathing? Please click on the correct answer: A. Hippocampus B. Limbic system C. Cerebellum D. Medulla

Answer: D The medulla oblongata is part of the brain stem and has important cardiac and respiratory functions. It is directly involved with the autonomic functions of things such as breathing, heart rate, and blood pressure.

Mg(OH)2 is slowly dissolved in 500 mL of 25oC water until the solution becomes fully saturated. Which of the following occurs when 10.0 mL of 0.1 M HCl is added? A. MgCl2 precipitates B. Mg(OH)2 precipitates C. Ksp for Mg(OH)2 increases D. [H2O] increases

Answer: D This question is testing your understanding of solution chemistry, equilibrium, and solubility rules. In a saturated solution of Mg(OH)2, the maximum concentrations of Mg2+(aq) and OH-(aq) ions have been reached and are in equilibrium with the solubility product, as follows: Mg(OH)2(s) ó Mg2+(aq) + 2OH-(aq) When HCl is added to the solution, the pH of the solution decreases. The additional H+ ions react with the dissolved OH- ions forming water. Thus, D is the correct answer. Magnesium chloride is soluble in water, eliminating choice A. When HCl is added, the hydroxide concentration decreases shifting the equilibrium to the right making Choice B false. The solubility product, Ksp, is a constant that varies only with temperature making choice C incorrect

At what stage does dormancy occur in primary oocytes? A. Metaphase I B. Prophase II C. Metaphase II D. Prophase I

Answer: D Primary oocytes begin the first meiotic division before birth but enter a prolonged period of dormancy during prophase I, choice (D). This dormancy lasts until puberty. Shortly before ovulation, the primary oocyte completes the first meiotic division due to an LH surge, giving rise to a secondary oocyte and a polar body. Upon ovulation, the secondary oocyte begins the second meiotic division and pauses at metaphase II. Choices (B) and (C) are incorrect because secondary oocytes, not primary oocytes, undergo prophase II and metaphase II. Choice (A) is incorrect because the primary oocyte does not enter metaphase I until shortly before ovulation.

At what point does crossing over between sister chromatids occur? A. During prophase of meiosis B. During prophase of mitosis C. During anaphase II of meiosis D. None of the above

Answer: D This is a tricky question that requires careful reading. Crossing over is a form of genetic recombination in which homologous chromosomes pair up and exchange pieces of their genetic material. Crossing over occurs in prophase I of meiosis, and is often referred to as synapsis. However, crossing over occurs between homologous chromosomes, and not between the sister chromatids of an individual chromosome. Sister chromatids are identical pieces of DNA joined at the centromere to make up one chromosome. Since crossing over doesn't occur between sister chromatids, the correct answer is (D).

Which of the following is true with regard to a major depressive episode? A. It may last less than two weeks. B. It must involve thoughts of suicide or a suicide attempt. C. It may involve a decrease in sleep. D. It must involve feelings of sadness.

C

Some enzymes require the presence of a non-protein molecule to behave catalytically. An enzyme devoid of this molecule is called a(n): A. holoenzyme B. apoenzyme C. coenzyme D. zymoenzyme

B. -An enzyme devoid of its necessary cofactor is called an apo-enzyme and is catalytically inactive.

In the equation below, substrate C is an allosteric inhibitor to enzyme 1. Which of the following is another mechanism caused by substrate C? A --> enzyme 1 --> B --> enzyme 2 --> C. A. Competitive inhibition B. Irreversible inhibition C. Feedback enhancement D. Negative feedback

D. -By limiting the activity of enzyme 1, the rest of the pathway is slowed, which is the definition of negative feedback. Choice (A) is incorrect because there is no competition for the active site with allosteric interactions. There is not enough information for (B) to be correct because we aren't told whether the inhibition is reversible. In general, allosteric interactions are temporary. Choice (C) is incorrect because is it the opposite of what occurs when enzyme 1 activity is reduced.

By weight, the adult human body is approximately 65% water, though certain tissues may have more or less water. Several samples of water are taken: one from the product of a combustion reaction, one from solid ice, and a final sample in the liquid phase. Which of the following explains/describes why all three of these samples have the molecular formula H2O? A. Constant composition B. Empirical formula C. Percent composition D. Steady-state

The law of constant composition, answer choice (A), explains that any sample of a given compound will contain the same elements in fixed proportions. Though the water samples are different in phase and in source, they are all still samples of H2O. As such, they will all have a 2:1 ratio of hydrogen to oxygen atoms, and they will all contain those elements in a fixed mass ratio. In addition to being the molecular formula for water, H2O is also its empirical formula, choice (B), but this does not explain why all three samples have the same composition. The percent composition, choice (C), is also the same for all three samples, but it would be the same for any compound with an empirical formula of H2O. Finally, steady-state, choice (D), refers to the state functions of a reaction, reactant(s), or intermediate(s), which are irrelevant to this question.