MCAT Biology Questions & Concepts
An inactive tetramer of IN is expected to have approximately what molecular weight?
128 kDa The passage indicates that an integrase monomer is composed of 288 amino acids, which will have an approximate molecular weight of 32 kDa (the average molecular weight of an amino acid is 110 Da). Thus, a tetramer will have an approximate molecular weight of 128 kDa.
A double-stranded DNA molecule contains bases with a ratio of (A + T)/(G + C) = 3:1. This molecule is replicated with DNA polymerase in the presence of the four deoxynucleoside triphosphates with a molar ratio of (A + T)/(G + C) = 1:1. What is the expected ratio of (A + T)/(G + C) in the double-stranded daughter DNA molecule?
3:1 The double stranded daughter DNA molecule would be an exact duplicate of the parent molecule. It would have the same (A + T)/(G + C) ratio.
Which of the following nucleotide sequences describes an antisense molecule that can hybridize with the mRNA sequence 5′-CGAUAC-3′?
3′-GCUAUG-5′
In a laboratory population of Drosophila, all the males are XsY. Among the females, 15% are XiXi, 50% are XiXs, and 35% are XsXs. Assuming random mating, what proportion of male flies in the next generation will be XiY?
40%
A vDNA sequence encoding a protein is inserted into a host genome by IN. The protein is translated from the hypothetical mRNA sequence shown. 5'-GGCAACUGACUA-3' Based on the passage, the segment of the original viral genome that encoded this protein had what nucleotide sequence?
5'-GGCAACUGACUA-3' According to the passage, viral DNA integrated into a host cell genome by integrase would originate from a retrovirus. mRNA transcribed from retroviral DNA is either used to synthesize viral proteins, or used as the RNA genome for progeny viruses. Thus, the sequence of the nucleotide in the original viral genome will be the same as that of the transcribed mRNA.
What is the net volume of fresh air that enters the alveoli each minute, assuming that the breathing rate is 10 breaths/min, the tidal volume is 800 mL/breath, and the nonalveolar respiratory system volume (dead space) is 150 mL?
6500 mL The amount of air entering the lungs in a single breath, or tidal volume, is given as 800 mL/breath. Of that 800 mL only 650 mL reaches the alveoli per breath (800 mL of air inhaled minus 150 mL of nonalveolar respiratory volume). Therefore the net volume of air that reaches the alveoli each minute is equal to 650 mL/breath multiplied by 10 breaths/min, or 6500 mL.
Assuming that the vertebrates were all of comparable size, which of the following vertebrates would be expected to have the strongest and heaviest bones?
A land-dwelling mammal Of the animals listed, a land-dwelling animal would be expected to have the heaviest bones, since enhanced bone density would be required to withstand the load bearing activity that results from the impact of gravity on land-dwelling animals. Less dense bones would be present in water-dwelling creatures and amphibians, since the impact of gravity would be ameliorated by life in an aquatic environment. Likewise less dense bones would be a necessity for flight.
After Sarah's accident, her attending physician detected the protein myoglobin in her urine. What type of injury is consistent with this observation?
After Sarah's accident, the physician detected myoglobin in Sarah's urine. Myoglobin is the substance that holds oxygen in the muscles and organs. The physician's observation is consistent with an injury to muscle or organs, but not bone.
Key Concept
Almost 100% of glucose filtrated into the nephron is reabsorbed back into the blood leaving no amounts that can be excreted in urine. Any higher concentration is a clear case of extreme hyperglycemia and glucose would start appearing in urine which can be confirmed with simple laboratory tests. This usually happens in diabetes and/or renal failure.
Which of the following changes would NOT interfere with the repeated transmission of an impulse at the vertebrate neuromuscular junction?
An increase in acetylcholine receptor sites on the motor end plate Addition of a cholinesterase blocker would produce a buildup of acetylcholine in the synapse and prevent receptors from responding to impulses.
Which statement below most accurately describes the roles of the proteins actin and myosin during muscular contraction?
Bridges between actin and myosin form, break, and re-form, leading to a shortening of muscle sarcomeres. The sliding filament model describes the interaction of actin and myosin during muscle contraction. According to this model, neuronal impulses cause the release of calcium from the sarcoplasmic reticulum within muscle cells. The calcium then binds to troponin, a molecule that along with tropomyosin, blocks the binding sites for myosin on actin molecules. Calcium binding to troponin causes a shift in the troponin/tropomyosin complex, revealing the binding site for myosin. Myosin then binds to actin, causing a conformational change in myosin that "cocks" the head of the myosin molecule and slides the actin filament relative to myosin. ATP binds to myosin, causing it to detach from actin and "recharge" (rebend again). If another binding site is available on actin, myosin will bind again, and slide the actin filament even further.
Key Concept
Calcium (Ca2+) is a vital element in the process of neurotransmitter release; when Ca2+ channels are blocked, neurotransmitter release is inhibited.
DDT would most likely initiate cancer or cause a mutation if which of the following structures is damaged?
Chromosome Mutations are heritable changes in the sequence of the nucleic acid component of chromosomes, and mutations that lead to unregulated cellular growth can lead to cancer
Control of heart rate, muscle coordination, and appetite is maintained by the:
Control of heart rate, muscle coordination, and appetite is maintained by the brain stem, cerebellum, and hypothalamus, respectively.
Aldosterone stimulates Na+ reabsorption by the kidneys. What changes in blood volume and pressure would be expected as a result of aldosterone deficiency?
Decreased volume and decreased pressure
The patient's ruptured appendix required treatment with antibiotics because he had a bacterial infection caused by:
E. coli entering the abdominal cavity from the appendix The appendix is continuous with the colon so that bacteria can move between these two structures; a ruptured appendix would allow E. coli into the abdominal cavity, which is not normal.
Which of the following experiments would best test the hypothesis that urease is necessary for the colonization of the stomach by H. pylori?
Exposing uninfected animals to a strain of H. pylori that lacks urease The most effective way to demonstrate necessity is to test for the occurrence of a specific outcome in the absence of the agent whose necessity is being tested.
If all genotypes are equally fit and if there are no genetic modifiers of the sex ratio trait, what will be the ultimate fate of a population in which 50% of the X chromosomes are currently Xi and 50% are Xs?
Extinction The passage states that if none of the Xi genotypes are selected against, then the Xi chromosome will increase to 100%. If all the males are XiY, then only females will be produced and the population will become extinct.
The amount of NE (norepinephrine) released by sympathetic nerve terminals will be most strongly influenced by a change in which of the following?
Extracellular [Ca2+] When an action potential reaches a nerve terminal it triggers the opening of Ca+ channels in the neuronal membrane. Because the extracellular concentration of Ca+ is greater than the intracellular Ca+ concentration, Ca+ flows into the nerve terminal. This triggers a series of events that cause the vesicles containing NE to fuse with the plasma membrane and release norepinephrine into the synapse.
What type or class of chemical messenger traveling in the blood would most probably link the brain with the digestive tract and fat cells in the control of body weight?
Hormones
Which event is directly mediated by a ligand-gated ion channel?
Influx of Na+ across the motor end plate resulting in the depolarization of the muscle fiber membrane The influx of Na+ across the motor end plate occurs when Na+ ion channels bind the ligand acetylcholine.
According to the hypothesis described in the passage, the bacteria that entered primitive eukaryotic cells were able to carry out which of the following functions that the primitive eukaryotic cells could NOT?
Krebs cycle and electron transport The bacteria are described as aerobic, so the passage suggests that the ability to use oxygen was acquired with the bacteria. Electron transport in mitochondria and bacteria is described and the electron transport system is needed for eukaryotes to use oxygen. The acquisition of aerobic bacteria as partners would have provided them with the ability to carry out aerobic metabolism through use of the Krebs cycle and electron transport.
One type of metabolic feedback loop that influences weight control involves the regulation of glucose levels in the blood. Which organ in the digestive system participates in this regulation by breaking down glycogen?
Liver In order to regulate blood glucose levels, glycogen is made, stored, and broken down in the liver. The chemical digestion of carbohydrates is initiated in the mouth, but is completed in the small intestine.
Delayed ovulation, as a cause of tubal pregnancy, would most likely be associated with delayed secretion of which of the following hormones?
Luteinizing hormone The question requires the examinee to identify that luteinizing hormone is the hormone responsible for triggering ovulation. While the sex hormones progesterone and estrogen are either secreted in response to the luteinizing hormone surge or actually trigger the luteinizing hormone surge, respectively, they are not directly involved in triggering ovulation. HCG is the pregnancy hormone, but it doesn't have a role in the typical ovulatory cycle.
Increased vasoconstriction has an important role in which of the following situations?
Maintaining blood pressure during a hemorrhage As blood is lost from the circulation, reduction in vessel size helps maintain the necessary pressure to keep the blood circulating to all body tissues. Vasoconstriction, the narrowing of a vessel, restricts blood flow to an organ and can increase blood pressure, whereas vasodilation has the opposite effect. Increased vasoconstriction is important in maintaining blood pressure during a hemorrhage. Vasodilation increases blood flow to both the muscle during exercise and the skin during blushing.
Of the following tissues, which is NOT derived from embryonic mesoderm?
Nerve Nervous tissue arises developmentally from ectoderm, not mesoderm. "means" oderm (the means of getting around as an organism, such as bones and muscle; the means of getting around in the body, such as the circulatory system; the means of "getting around", such as the gonads)
Capillaries in the kidney and elsewhere in the body maintain fluid homeostasis by balancing hydrostatic and osmotic pressures. Which of the following is the initial effect of a blood clot forming on the venous side of a capillary bed?
Net fluid flow in the direction of interstitial spaces will increase It is necessary to know that blood flows from arteries to capillaries and then to veins. If flow is blocked at the venous side, blood would accumulate in the capillaries. Thus, hydrostatic pressure would build up in the capillaries, causing a net increase in fluid flow into the interstitial spaces. Osmotic pressure wouldn't increase, because the osmolarity of the blood wouldn't change. Hydrostatic pressure would increase inside the capillaries; in other words, the blood would be "pushing" on the walls of the capillaries, which would cause more fluid diffusion out of the capillaries and into the interstitial spaces. This would happen anywhere there was a blockage and increased pressure, it is not specific to the kidneys.
A student postulated that the sodium pump directly causes action potentials along neurons. Is this hypothesis reasonable?
No; action potentials result in an increased permeability of the plasma membrane to sodium.
Would an increase in the level of plasma aldosterone be expected to follow ingestion of excessive quantities of NaCl?
No; aldosterone causes Na+ reabsorption by kidney tubules Aldosterone, which is produced by the adrenal cortex, causes Na+ reabsorption by kidney tubules. Such a mechanism decreases Na+ levels in the urine. The steroid aldosterone does not cause Na+ secretion into the urine. Because ingestion of excessive NaCl would trigger Na+ secretion into the urine, plasma-aldosterone levels would not increase. Rather, the body would rely on those homeostatic mechanisms that excreted the excess Na+. Thus an increase in plasma aldosterone would not be expected to follow ingestion of large quantities of NaCl.
In eukaryotic cells, the process of incorporating uridine nucleotides into nucleic acid polymers occurs in which of the following structures of the cell?
Nucleus Uridine nucleotides are incorporated into RNA, and the question is therefore asking where transcription occurs. In a eukaryotic cell, transcription occurs in the nucleus.
Key Concept
One characteristic that distinguishes eukaryotic cells from prokaryotic cells is that eukaryotic cells contain membrane-bound organelles such as mitochondria
Key Concept
One of the key differences between mitosis and meiosis occurs during their respective anaphases. During anaphase of mitosis, sister chromatids are pulled apart at the centromeres, each becoming an independent chromosome in the two diploid daughter cells. During anaphase I of meiosis I, homologous pairs of chromosomes are separated into the two daughter cells. However, each chromosome still consists of two sister chromatids joined to each other at the centromere. It is not until anaphase II of meiosis II that the centromere is split and the sister chromatids separate.
Key Concept
Only serine (has an OH) can be phosphorylated!
Radioactively labeled uracil is added to a culture of actively dividing mammalian cells. In which of the following cell structures will the uracil be incorporated?
Ribosomes Uracil is a component of RNA. Therefore, one would expect to find the radioactively labeled uracil in cell structures that contain RNA. B is the best answer because ribosomes contain rRNA and proteins. A is incorrect because chromosomes, by definition, consist primarily of proteins and DNA. Although DNA is composed of nucleic acids, DNA contains thymine instead of uracil. C and D are incorrect because RNA is not an integral component of either lysosomes (C) or the nuclear membrane (D).
What would be the result of complete removal of the parathyroid glands?
Severe neural and muscular problems due to deficiency of calcium in the plasma Removal of the parathyroid gland would lead to hypocalcemia, a condition of low blood calcium, resulting from the lack of parathyroid hormone. This would cause increased neuromuscular excitability because of the change in membrane potential, which under normal physiological conditions, is partially kept in balance with extracellular calcium.
Which of the following organelles most resembles the Golgi apparatus when an intact eukaryotic cell is viewed under the electron microscope?
Smooth endoplasmic reticulum The smooth endoplasmic reticulum most resembles the Golgi apparatus in an intact eukaryotic cell when viewed under the microscope. Both organelles appear to be membranes with many folds.
If the dose of Streptococcus Strain A required to cause infection is 1 x 105 bacteria and that of Streptococcus Strain B is 5 x 104 bacteria, which of the following statements describes the relative potencies of these strains?
Strain A is half as potent as Strain B
The extreme hyperglycemia of these animals suggests that major changes in the normal glucose regulatory mechanisms occur during freezing. Which of the following observations would support this hypothesis?
Suppression of insulin secretion during freezing episodes
Which of the two hypotheses in the passage most closely fits the present-day understanding of human differentiation?
The Regulative Hypothesis, because each embryonic cell receives a complete set of genes, and cell position helps to determine differentiation
Why do calcium supplements often include vitamin D?
The activated form of vitamin D stimulates the absorption of calcium into the blood
If oligonucleotides such as mRNA were not degraded rapidly by intracellular agents, which of the following processes would be most affected?
The coordination of cell differentiation during development The destruction of mRNA prevents continuous protein production, allowing the cell to change its protein expression over time.
From which germ layer(s) do the tissues of the heart and blood vessels differentiate?
The heart and blood vessels both differentiate from the mesoderm
In which organelle of a eukaryotic cell is the pyrimidine uracil, as part of uridine triphosphate (UTP), incorporated into nucleic acid?
The nucleus The nitrogenous base, uracil, combined with the sugar ribose and phosphate makes up the nucleotide uridine. It is found in RNA, but not in DNA. The corresponding DNA nucleotide is thymine. Uridine is incorporated into RNA in the nucleus where transcription of DNA into RNA takes place. RNA is manufactured in the nucleus from a DNA template.
Which of the following changes in flow rate or in solute concentrations would NOT occur if the blood inflow rate were increased, increasing the pressure in the dialysis chamber?
The osmotic concentration of proteins in the dialysate fluid would increase. The osmotic concentration of proteins would not be expected to increase in the dialysate fluid because proteins generally do not pass through the membrane.
To support the symbiotic hypothesis presented in the passage, mitochondria should be similar to bacteria in which of the following ways?
They should have circular DNA The fact that both have circular DNA supports the symbiotic hypothesis presented in the passage. Alternative choices presented are not actually true characteristics of bacteria. Bacteria do have 70S ribosomes, not the 80S ribosomes of eukaryotes and they do reproduce by binary fission. The loss of ability to carry out anaerobic respiration might be a product of the long history of association with the host cell. It is not unusual for symbiotic organisms to lose abilities that are compensated for by host functions.
Key Concept
When a vertebrate oocyte divides in meiosis the cytoplasm is distributed to the two daughter cells. Most of it goes to the daughter cell destined to be the ovum. The other daughter cells, the polar bodies, are cast off with little cytoplasm. The amount of nuclear material in each, however, is the same.
Under what condition would the level of calcitonin tend to increase?
When the level of calcium in the plasma is high Calcitonin reduces bone resorption. Bone resorption occurs when the level of calcium in the blood plasma is low, but resorption is not needed when the level of calcium is high. Therefore, resorption would be reduced by calcitonin under conditions in which the level of calcium in the plasma is high.
A virgin female Drosophila mates and produces 34 daughters and 38 sons. Eighteen of these sons sire only daughters, while the remainder sire approximately equal numbers of daughters and sons. What are the genotypes of the original female and the male with whom she mated?
XiXs and XsY The male parent must have been XsY or there would only have been daughters in the offspring of the first generation, so options B and D are incorrect. If the female had been XiXi then all its sons would have had only daughters, but twenty of the sons have both sons and daughters, so option C cannot be correct.
Which of the following statements best explains why Xi has the potential to increase to 100% frequency in gene pools that contain it?
XiY flies pass their X chromosome to all their offspring, but XsY flies pass their X chromosome to only half their offspring "An XsY male is standard: he sires equal numbers of sons and daughters. An XiY male expresses the sex ratio trait: he sires only daughters."
If the e and f genes are expressed, the Xi chromosome will be prevented from reaching 100% frequency if selection pressures cause which of the following to be true?
XsXs flies have the highest fitness of any genotype The passage says that, if none of the Xi bearing genotypes is selected against, the frequency of Xi will increase to 100%.
Most proteins in present-day mitochondria are made by cytoplasmic ribosomes from mRNA transcribed from nuclear genes. Can this fact be reconciled with the hypothesis described in the passage?
Yes; the transfer of genes from symbionts to the eukaryotic nucleus could have occurred during the last billion years of evolution. The endosymbiotic theory described in the passage is widely accepted today, so there must be some way of using the theory to reconcile the fact that mitochondrial proteins are made in the cytoplasm. We know, for example, that lateral transfer of genes from one genome to another is widespread among living organisms. It would have been an easy matter for mitochondrial genes to be acquired by the host cell nucleus and to disappear from the mitochondrial genome. It is likely that this exchange would have resulted in a net gain in efficiency for the composite organism.
cerebellum
a large structure of the hindbrain that controls fine motor skills
If a cell's membrane potential changes from -60mV to -70mV after treatment with an adrenergic drug, the NE receptor is most likely linked to:
a potassium channel
Haversian canal
any of the minute tubes which form a network in bone and contain blood vessels
function of the pancreas
carbohydrate, protein, and fat digestion - secretes amylase to break down large polysaccharides into small disaccharides - secretes trypsin, chymotrypsin, and carboxypeptidases in zymogen form and once activated are responsible for protein digestion - secretes lipases to break down fats to fatty acids and monoglycerides
When viewing an X ray of the bones of a leg, a doctor can tell if the patient is a growing child, because the X ray shows:
cartilaginous areas in the long bones Long bones grow via endochondral ossification, which requires cartilaginous growth plates at the ends of long bones, that thicken as cartilage and later become ossified. Dividing bone cells and Haversian canals can be present in fully ossified adult bones. Some adults who are short in stature may have fully ossified long bones that are shorter than those of a developing child.
Assume that NO is continuously synthesized. The addition of a saturating concentration of L-NMMA to a relaxing aortic ring with intact endothelium would probably:
cause the ring to contract (increase its tension) The passage states that L-NMMA is an inhibitor of NO synthetase, which is responsible for the synthesis of nitric oxide (NO). NO serves as the relaxing compound. If NO synthesis in intact endothelium was inhibited by addition of a saturating concentration of L-NMMA, one would expect that the tension of the aortic ring would increase.
In almost all vertebrates, when the optic cup fails to develop in the embryo, the lens also fails to form. This constitutes evidence that:
cells may induce neighboring cells to differentiate The optic cup develops from a bulge on the side of the developing brain, which influences the overlying ectoderm to produce the lens.
At the end of his initial hospital stay, a few E. coli cells remained in the patient's colon, even though he was taking antibiotics. These cells were most likely present because:
chance mutations in a few E. coli before the treatment made these cells and their descendants antibiotic-resistant Mutations which make cells drug resistant are very rare, but the few drug-resistant bacteria that do develop such mutations flourish when the nonresistant cells are killed by antibiotics. Antibiotics are unlikely to have been the source of the mutations; nor do bacteria develop "immune" reactions to antibiotics. Any resistance of the patient's own colon cells to antibiotics is irrelevant to the resistance of bacteria to antibiotic.
The persistence of a pulse for several hours after the onset of ice formation (Figure 1) is crucial to the cryoprotective role of glucose because:
circulating blood distributes the glucose throughout the body tissues
bacteria can exchange genes through 3 processes
conjugation: DNA is transferred between bacteria through a tube between cells transformation: a bacterium takes up a piece of DNA floating in its environment transduction: DNA is accidentally moved from one bacterium to another by a virus
brain stem
controls the flow of messages between the brain and the rest of the body, and it also controls basic body functions such as breathing, swallowing, heart rate, blood pressure, consciousness, and whether one is awake or sleepy
A bacterium containing genes for sex pilus construction gave rise to a daughter cell lacking these genes. This most probably occurred because:
copies of the plasmid containing the genes were not equally distributed to the new daughter cells
The chemical valinomycin inserts into membranes and causes the movement of K+ into the mitochondria. Based on Figure 1, if mitochondria are treated with valinomycin, the rate of ATP synthesis in the mitochondria will most likely:
decrease, because movement of K+ into the mitochondrial compartments will disrupt proton movement into the intermembrane space The question does provide the information that valinomycin increases the flow of K+ across the membrane. An influx of another positively charged ion into the compartment would disrupt the electrochemical gradient responsible for the necessary flow of protons.
The chemical gramicidin inserts into membranes and creates an artificial pathway for proton movement. Based on Figure 1, if mitochondria are treated with gramicidin, the rate of ATP synthesis will most likely:
decrease, because the proton gradient will rapidly reach equilibrium Hydrogen ions (H+) are protons. The provision of a channel for proton flow across the membrane would allow hydrogen ions to flow across the membrane until equilibrium had been achieved between the concentrations on each side of the membrane. Because ATP synthesis is driven by a flow of hydrogen ions down a concentration gradient, ATP production will decrease and eventually stop as equilibrium is established.
hypoxia
deficiency in the amount of oxygen reaching the tissues
Which of the following processes is LEAST directly influenced by adrenergic drugs?
enzymatic breakdown of food molecules According to the passage, adrenergic drugs mimic activation of the sympathetic nervous system; therefore, the best answer will be the process that is LEAST directly controlled by the sympathetic nervous system. The sympathetic nervous system directly inhibits peristalsis and secretion of digestive enzymes. It also increases the blood glucose concentration and causes dilation of the blood vessels that supply the deep muscles and internal organs, which aids nutrient delivery to these tissues. The sympathetic nervous system does not directly affect the activity of digestive enzymes after they have been secreted.
The stereochemical designators α and β distinguish between:
epimers at an anomeric carbon atom
People who are born without sweat glands are likely to die of heat stroke in the tropics. This indicates that, under tropical conditions, the human body may:
gain, rather than lose, heat by radiation These individuals are forced to rely nearly solely on vasodilation (radiation) rather than sweating (evaporation) for responding to elevated external temperatures. That individuals without sweat glands are likely to suffer heat stroke in the tropics, indicates that radiation alone is ineffective for cooling under these conditions. In fact, the human body may gain heat by absorbing radiation from the sun leading to an elevation in body temperature
H. pylori infection may cause increased proliferation of mucosal cells in the stomach. This may lead to gastric cancer if:
genetic mutations occur in proliferating somatic cells. If H. pylori infection causes increased proliferation of mucosal cells in the stomach, this could lead to gastric cancer if genetic mutations occur in proliferating somatic cells that line the stomach.
Presumably, hyperglycemia promotes cellular dehydration because:
glucose molecules raise the osmotic pressure of the extracellular space. more solute = higher osmotic pressure
Bicarbonate ions in the blood and the dialysate are important for maintaining physiological levels of:
hydrogen ions
The prolonged increase in heart and breathing rates during the snow skiing trip was probably a result of:
hypoxia caused by insufficient blood hemoglobin concentration to supply oxygen for exercise at the low oxygen pressure found at high altitudes
Kidney failure during severe dehydration is most likely due to:
inadequate blood volume for effective filtration Severe dehydration greatly reduces the volume of filtrate moving through the nephrons of the kidney. If fluid volume is too drastically reduced, the kidney will be unable to effectively do its job of filtering and maintaining homeostasis within bodily fluids.
Key Concept
increased blood pressure will increase the glomerular filtration rate
An effective and efficient method for the delivery of an antisense gene could be:
infection of an embryo by a virus modified to carry the gene The best way to deliver the antisense gene into all the cells of the individual would be to infect an embryo with a virus that carries the antisense gene. The appropriate virus could become incorporated into the genome of the embryonic cells, thus causing all cells derived from these embryonic cells to contain the antisense gene.
An intravenous infusion causes a sharp rise in the serum level of albumin (the major osmoregulatory protein in the blood). This will most likely cause an:
influx of tissue fluid to the bloodstream
Which organ is involved in regulation of all of the following: acid-base balance, blood pressure, water balance, and removal of nitrogen wastes?
kidney
Key Concept
leukocytes gravitate toward an inflammation
According to the information in the passage, which statement best describes the function of the MR (myogenic response) in response to stimulation of the sympathetic nervous system? The MR:
moderates blood flow to the brain under high pressure MR is a local response in resistance vessels that would slow blood flow to the brain to reduce the chance of tissue damage from high blood pressure resulting from activation of the sympathetic nervous system. During activation of the sympathetic nervous system blood flow is directed towards the brain and skeletal muscles, and not to organs in the abdominal cavity. Blood pressure is higher in the aorta than in the rest of the body!
function of the stomach
mostly mechanical, some chemical digestion of proteins
A low level of calcium in the plasma will trigger an increase of:
osteoclast activity and parathyroid hormone When the level of calcium in the blood plasma is low, the body responds by mobilizing stores of calcium from the bones via the activity of parathyroid hormone. Parathyroid hormone will increase the number of osteoclasts, which break down bone cells. Therefore, one would expect an increase in both parathyroid hormone and osteoclast activity in order to increase the level of calcium in the blood plasma (options I and II). However, vitamin C (option III) promotes bone formation, a process that would further lower the calcium level in the plasma.
The osmotic concentration of plasma proteins in the venous side of capillaries helps reduce the amount of interstitial fluid in tissues by inducing:
passive H2O diffusion along a concentration gradient
In eukaryotes, oxidative phosphorylation occurs in the mitochondrion. The analogous structure used by bacteria to carry out oxidative phosphorylation is the:
plasma membrane The inner membrane of a mitochondrion is analogous to the plasma membrane of a prokaryote. The enzymes for oxidative phosphorylation are embedded in the inner membrane. The endosymbiotic theory suggests that mitochondria are descendants of prokaryotes that were engulfed by endocytosis into a vesicle lined with a membrane derived from the cell membrane of the eukaryote host. The inner membrane used to be the plasma membrane!
When the environmental temperature is 33° C, vasodilation of cutaneous blood vessels helps to regulate the body temperature of a human by:
radiating excess body heat into the environment When vasodilation occurs, the walls of blood vessels relax, allowing more blood to enter the area. The presence of increased blood within dilated vasculature in cutaneous tissue allows heat to escape from the surface of the body into the environment
If DDT accumulates in the liver, all of the following bodily functions may be significantly impaired EXCEPT:
regulation of blood pressure The detoxification of poisons and the production of bile, which facilitates fat absorption in the small intestine by breaking large fat droplets into smaller ones, are major liver functions.
In the macronucleus, the genes for rRNA are located extrachromosomally. This suggests that the rRNA genes are:
self-replicating Genes are strands of DNA, so this must mean that they are strands of DNA that are not part of the cell's chromosomes. These strands still must self-replicate just as the chromosomes do if they are to be passed from one generation to the next.
Symptoms of burning, itching, and pain occur when DDT is absorbed through the skin because:
sensory neurons are depolarized
Accumulation of DDT in the testes may cause reduced fertility in males because the uncoupling of oxidative metabolism from ATP production may reduce:
sperm motility Sperm motility requires large amounts of ATP as evidenced by the high concentration of mitochondria in the sperm midpiece.
The outer layers of human skin are composed of dead cells impregnated with keratin and oil, which make the epidermis relatively impermeable to water, yet humans sweat freely in hot temperatures. This occurs because:
sweat glands have special channels through the skin The sweat glands secrete onto the surface of the skin through channels continuous with the most superficial layer of the skin, the epidermis. These channels prevent water loss by isolating the water-permeable, sweat-secreting cells from dry surface air. The openings of the sweat glands on to the surface of the epidermis are pores.
Most bacterial cells and human cells are alike in:
the ability to produce ATP via ATP synthase The chemical composition of prokaryotic and eukaryotic ribosomes (B), although similar, is distinct enough that several types of antibiotics are able to preferentially target prokaryotic ribosomes over eukaryotic ribosomes. Of human and bacterial cells, only bacterial cells have cell walls (C), and most bacterial chromosomes are circular whereas human chromosomes are linear (D).
The two primary factors that normally determine the level of blood pressure are:
the cardiac output and the resistance to blood flow Two factors that normally determine the blood pressure are the cardiac output and the resistance to blood flow. Cardiac output (stroke volume x heart rate) determines the amount of blood pumped into the system by the heart per unit time. The resistance to blood flow is primarily determined by the caliber of the small arteries, arterioles, and precapillary sphincters.
lymph
the clear, slightly alkaline, bodily fluid bathing body tissues containing mostly of white blood cells
Muscles with striated fibers are the primary muscle type in:
the heart Skeletal and cardiac muscles contain striated muscle fibers. Smooth muscles do not. The heart is made of cardiac muscle and therefore has striated muscle fibers. The primary muscle type of the uterus, arteries and veins, and the small intestine is smooth muscle.
pituitary gland
the major endocrine gland. A pea-sized body attached to the base of the brain, the pituitary is important in controlling growth and development and the functioning of the other endocrine glands.
ossification
the process of bone formation
Krebs cycle
the sequence of reactions by which most living cells generate energy during the process of aerobic respiration. It takes place in the mitochondria, consuming oxygen, producing carbon dioxide and water as waste products, and converting ADP to energy-rich ATP.
Two neighboring lizard populations would be considered separate species if:
they did not interbreed and produce fertile offspring
If a person's gallbladder is removed, the person should restrict the consumption of:
triglycerides The gallbladder is responsible for storing bile, which is produced by the liver to break up fat
Tests performed on the M. tuberculosis strain infecting the patient's coworker indicated that the strain was susceptible to both ampicillin and kanamycin, and the coworker was successfully treated. The M. tuberculosis most likely survived in the patient because it had:
undergone conjugation with cells of resistant E. coli