AP BIO: Unit 4 MCQ Review

Cancer can result from a variety of different mutational events. Which of the following is LEAST likely to result in the initiation of a cancerous tumor? A. A receptor mutation results in activation of a cell-division pathway in the absence of the appropriate ligand. B. A mutation results in the loss of the ability to produce a tumor-suppressor protein. C. A defect in a cell-cycle checkpoint prevents a cell from entering the S phase. D. At the anaphase checkpoint, separation of chromatids occurs without all centromeres being attached to kinetochore microtubules from both poles.

Most cells that have become transformed into cancer cells have which of the following characteristics when compared to normal, healthy cells? A. Shorter cell cycles B. More carefully regulated rates of cell division C. Lower rates of mitosis D. Higher rates of protein translation E. Identical DNA

The brain coordinates the circulatory and respiratory systems of the human body. The control of breathing, for example, involves neural pathways among the structures represented in the figure above. One important stimulus in the control of breathing is an increase in blood CO2 concentration, which is detected as a decrease in blood pH. Which of the following best describes the physiological response to an overall increase in cellular respiration in the body? A. In response to depleted blood CO2 levels, the pH sensors send signals directly to the rib muscles, resulting in an increase in the rate of CO2 uptake by the lungs and a decrease in CO2 utilization by the brain. B. In response to low blood pH, the pH sensors send a signal to the brain, which then sends a signal to the diaphragm, resulting in an increased rate of breathing to help eliminate excess blood CO2 . C. In response to high blood pH, the pH sensors send a signal directly to the lungs, resulting in a slower rate of breathing, and the lungs send a signal back to the heart once CO2 availability has been restored. D. In response to an increased rate of breathing, the rib muscles send a signal to the brain, which then sends a signal to the heart, resulting in a decrease in heart activity and slower flow of blood through the body.

Ethylene is an organic compound produced by ripening fruits. In a controlled experiment, researchers found that ethylene gas stimulated the ripening process in newly harvested fruits. Which of the following describes the most likely connection between natural ethylene production and fruit ripening? A. As a result of metabolic inactivity, newly harvested fruits are unable to absorb ethylene gas from the atmosphere. B. Ethylene gas is a chemical signal through which ripening fruits trigger the ripening process in other fruits. C. Because of normal phenotypic variation, only some of the fruits in a given generation are expected to produce ethylene gas. D. The rate of ethylene gas production by ripening fruits is an indicator of the relative age of an ecosystem.

Which of the following statements best describes how a growth factor stimulates cell division from outside a cell? A. The growth factor binds to other cells in the same area and holds them together to form a large, multicellular structure. B. The growth factor binds to receptors on the cell surface, initiating a signal transduction pathway that activates specific target genes. C. The growth factor binds to sugar molecules in the extracellular fluid and provides them to the cell as a source of energy. D. The growth factor binds to phospholipids in the plasma membrane, creating a channel through which substances enter the cell.

Which of the following best represents two different signaling pathways that share a second messenger?

Which of the following is true of mitosis? A. It is also known as cytokinesis. B. It maintains the same chromosome number in the daughter cells as in the parent cell. C. It is the last phase of interphase. D. It regulates the transfer of genetic information from one daughter cell to another. E. It moves homologous chromosomes to opposite poles.

Cell communication is critical for the function of both unicellular and multicellular eukaryotes. Which of the following is likely true of cell signaling? A. Cell signaling uses the highest molecular weight molecules found in living cells. B. Cell signaling has largely been replaced by other cell functions in higher mammals. C. Similar cell signaling pathways in diverse eukaryotes are evidence of conserved evolutionary processes. D. Cell signaling functions mainly during early developmental stages.

Researchers investigating the regulation of neurotransmitter release from presynaptic neurons proposed a model (Figure 1) in which CDK5, a protein expressed in axon terminals, inhibits the movement of synaptic vesicles to the presynaptic membrane. To test their model, the researchers used a modified version of green fluorescent protein (GFP*). In slightly alkaline conditions, GFP* exhibits a bright green fluorescence. In acidic conditions, GFP* exhibits no fluorescence. Using standard techniques, the gene encoding is easily introduced into living cells. By engineering the expression of GFP* in laboratory-cultured nerve cells, the researchers found that a bright green fluorescence was exhibited only when a presynaptic neuron was given a certain stimulus. Which of the following observations best supports the hypothesis that negatively regulates neurotransmitter release? A. Introduction of CDK5 protein into neurons results in the movement of synaptic vesicles to the plasma membrane in the absence of any stimulus. B. Uptake of a gene encoding CDK5 by neurons results in the movement of synaptic vesicles to the plasma membrane in the absence of any stimulus. C. Suppression of CDK5 expression in neurons inhibits the movement of synaptic vesicles to the plasma membrane in response to a specific stimulus. D. Inhibition of CDK5 activity in neurons increases the movement of synaptic vesicles to the plasma membrane in response to a specific stimulus.

The figure above shows a model of a ligand precursor being cleaved to produce an active ligand that binds to a specific receptor. Which of the following is most likely to reduce the binding of the active ligand to its receptor? A. A change in the cytoskeletal attachment of transmembrane proteins B. The presence of a large amount of the precursor form of the ligand C. An increase in the ratio of the number of unsaturated to the number of saturated fatty acid tails of the membrane lipids D. A mutation in the receptor gene that causes a substitution of a charged amino acid for a nonpolar amino acid in the ligand binding site of the receptor

The diagram above represents a model of signal transduction pathways (I and II) in a cell that is targeted by two different hormones (H1 and H2). The components of the signal transduction pathways are identified in the figure legend. Each cellular molecule in both pathways can exist in an inactive or active form. When the components in pathway I are sequentially activated, the TAP molecules promote cell division. When the components in pathway II are sequentially activated, downstream signaling by the G protein is inhibited. Based on the model, which of the following mutations is most likely to result in a cell that will generate a cancerous tumor? A. A mutation in the gene encoding PP that results in a nonfunctional protein B. A mutation in the gene encoding G-PIP that results in a nonfunctional protein C. A mutation in the gene encoding R1 so that it is inactive even in the presence of H1 D. A mutation in the gene encoding R2 so that it is active even in the absence of H2

Thyroxin is a hormone that increases metabolic activities within various tissue targets. Low levels of circulating thyroxin trigger the secretion of thyroid-stimulating hormone (TSH) from the anterior pituitary. TSH secretion then stimulates thyroxin production and release by the thyroid gland. The increased level of circulating thyroxin inhibits further secretion of TSH from the anterior pituitary. Based on the information provided, which of the following can most likely be concluded about the TSH-thyroxin loop? A. A person taking thyroxin to supplement low thyroxin secretion will produce more TSH. B. Increased thyroxin production would cause elevated ribosomal activity in the anterior pituitary. C. The structure of the loop would lead to elevated thyroid and tissue activity due to positive feedback. D. The feedback mechanism would maintain relatively constant levels of thyroxin throughout tissue targets.

In response to elevated blood glucose levels, beta (β) cells in the pancreas release insulin, a regulatory hormone. Insulin signals body cells to take up glucose from the blood, which returns blood glucose levels back to normal. Type 1 diabetes is an autoimmune disorder that destroys β-cells, resulting in elevated blood glucose levels. Researchers have proposed that diabetes could be treated by implanting human embryonic stem cells (hESCs) that have been induced to develop into β-cells (hESC-β). To test the proposed treatment, the researchers set up two groups of genetically identical mice and implanted the mice from one group with hESC-β cells. Several weeks after the hESC-β implant, both groups of mice were given a drug (STZ) that selectively destroys the naturally occurring mouse β-cells but does not affect the implanted hESC-β cells. Figure 1 shows a comparison of average blood glucose levels in both groups of mice. A. The mouse with an hESC-β implant demonstrated a decrease in blood glucose levels for the duration of the experiment. B. The mouse with an hESC-β implant demonstrated an increase in blood glucose levels before STZ treatment. C. The mouse with an hESC-β implant successfully regulated blood glucose levels by regenerating its naturally occurring β-cells. D. The mouse with an hESC-β implant successfully regulated blood glucose levels after STZ treatment but not after the implant was removed.

In response to elevated blood glucose levels, beta (β) cells in the pancreas release insulin, a regulatory hormone. Insulin signals body cells to take up glucose from the blood, which returns blood glucose levels back to normal. Type 1 diabetes is an autoimmune disorder that destroys β-cells, resulting in elevated blood glucose levels. Researchers have proposed that diabetes could be treated by implanting human embryonic stem cells (hESCs) that have been induced to develop into β-cells (hESC-β). To test the proposed treatment, the researchers set up two groups of genetically identical mice and implanted the mice from one group with hESC-β cells. Several weeks after the hESC-β implant, both groups of mice were given a drug (STZ) that selectively destroys the naturally occurring mouse β-cells but does not affect the implanted hESC-β cells. Figure 1 shows a comparison of average blood glucose levels in both groups of mice. A The treatment would fail because insulin produced by implanted hESC-β cells will not stimulate glucose uptake by body cells. B The treatment would fail because the implanted hESC-β cells would require more glucose than the body can produce. C The treatment would succeed because the implanted hESC-β cells can express the gene that codes for human insulin. D The treatment would succeed because the body cells would secrete more insulin in the presence of the implanted hESC-β cells.

In response to elevated blood glucose levels, beta (β) cells in the pancreas release insulin, a regulatory hormone. Insulin signals body cells to take up glucose from the blood, which returns blood glucose levels back to normal. Type 1 diabetes is an autoimmune disorder that destroys β-cells, resulting in elevated blood glucose levels. Researchers have proposed that diabetes could be treated by implanting human embryonic stem cells (hESCs) that have been induced to develop into β-cells (hESC-β). To test the proposed treatment, the researchers set up two groups of genetically identical mice and implanted the mice from one group with hESC-β cells. Several weeks after the hESC-β implant, both groups of mice were given a drug (STZ) that selectively destroys the naturally occurring mouse β-cells but does not affect the implanted hESC-β cells. Figure 1 shows a comparison of average blood glucose levels in both groups of mice. A Decreased insulin secretion by body cells → increased glucose uptake by mouse β-cells → increased insulin secretion by body cells B Increased insulin production by mouse β-cells → increased glucose uptake by hESC-β cells → decreased glucose metabolism by body cells C Increased insulin secretion by hESC-β cells → increased glucose uptake by body cells → decreased insulin secretion by hESC-β cells D Increased metabolism of glucose by hESC-β cells → differentiation of hESC-β cell into body cells → increased glucose production by body cells

The model shown in the figure represents the role of two hormones, calcitonin and parathyroid hormone (PTH), in maintaining normal blood calcium levels in humans. If a dietary change results in an increase in blood calcium concentration above normal levels, which of the following is the most likely effect on calcium homeostasis? A Calcitonin levels will decline, thus stimulating the release of PTH. B Calcitonin levels will rise, thus promoting the deposit of calcium into bones. C PTH levels will decline, thus stimulating the loss of calcium from bones. D PTH levels will increase, thus preventing the release of calcitonin.

Which of the following best describes the role of mitosis in the cell cycle? A Distributing replicated chromosomes to daughter nuclei B Dividing the cytoplasm to form four gametes C Producing organelles and replicating chromosomes D Exchanging genetic material between homologous chromosomes

The endocrine system incorporates feedback mechanisms that maintain homeostasis. Which of the following demonstrates negative feedback by the endocrine system? A During labor, the fetus exerts pressure on the uterine wall, inducing the production of oxytocin, which stimulates uterine wall contraction. The contractions cause the fetus to further push on the wall, increasing the production of oxytocin. B After a meal, blood glucose levels become elevated, stimulating beta cells of the pancreas to release insulin into the blood. Excess glucose is then converted to glycogen in the liver, reducing blood glucose levels. C At high elevation, atmospheric oxygen is more scarce. In response to signals that oxygen is low, the brain decreases an individual's rate of respiration to compensate for the difference. D A transcription factor binds to the regulatory region of a gene, blocking the binding of another transcription factor required for expression.

The Hedgehog protein (Hh) plays a critical role during a certain period of embryo development, but it normally has no role in adults except for the maintenance of adult stem cells. However, the Hedgehog protein has been detected in 70 percent of pancreatic cancer cell samples. As illustrated in the figures below, the Hedgehog protein binds to an integral membrane protein receptor known as Patched (Ptc), thus initiating a pathway of gene expression. When Hedgehog is absent, Ptc inhibits another protein known as Smoothened (Smo), which, in turn, blocks the activation of a group of proteins collectively known as the Hedgehog signaling complex (HSC). The inactivation is the result of proteolytic cleavage of one component of the HSC complex, a transcription factor known as Cubitus interruptus (Ci). When Hedgehog is present, it binds to Ptc, which prevents the inhibition of Smo by Ptc. The result is that Ci remains intact and can enter the nucleus, where it binds to and activates certain genes. A Treating patients with a molecule that is structurally similar to Hedgehog and that will bind to and interact with Ptc in the same fashion as Hedgehog B Injecting patients with embryonic cells so that Hedgehog will bind to those cells instead of the cancer cells C Treating patients with a membrane-soluble compound that can bind to Smo and block its activity D Injecting patients with a preparation of purified membrane-soluble Ci that will enter the nuclei of the cancer cells and induce gene transcription

In mammals, an increase in the concentration of sodium in the blood triggers the release of antidiuretic hormone (ADH) from the pituitary gland. As the concentration of sodium in the blood returns to previous levels, the release of ADH from the pituitary gland is reduced. Based on the information presented, which of the following describes the most likely role of ADH in maintaining blood osmolarity? A ADH promotes an increase in the movement of sodium into the bloodstream. B ADH promotes an increase in the movement of water into the bloodstream. C ADH promotes an increase in the excretion of water from the body. D ADH promotes an increase in the secretion of additional ADH from the pituitary gland.

Epinephrine is a protein hormone found in many animals. Epinephrine stimulates a signaling pathway that results in the breakdown of glycogen to glucose in the liver cells. Which of the following describes the initial steps in the process whereby epinephrine stimulates glycogen breakdown? A Epinephrine binds to a cell-surface receptor; the activated receptor stimulates production of the second messenger, cAMP. B Epinephrine binds to a cell-surface receptor; the activated receptor catalyzes the conversion of glycogen to glucose. C Epinephrine diffuses through the plasma membrane; the hormone dimerizes in the cytosol. D Epinephrine is taken into the cell by endocytosis; glycogen is converted to glucose in the endocytotic vesicle.

Antidiuretic hormone (ADH) is important in maintaining homeostasis in mammals. ADH is released from the hypothalamus in response to high tissue osmolarity. In response to ADH, the collecting duct and distal tubule in the kidney become more permeable to water, which increases water reabsorption into the capillaries. The amount of hormone released is controlled by a negative feedback loop. Based on the model presented, which of the following statements expresses the proper relationship between osmolarity, ADH release, and urine production? A As tissue osmolarity rises, more ADH is released, causing less water to be excreted as urine. B As tissue osmolarity rises, less ADH is released, causing less water to be excreted as urine. C As tissue osmolarity rises, more ADH is released, causing more water to be excreted as urine. D As tissue osmolarity rises, less ADH is released, causing more water to be excreted as urine.

The diagram above illustrates feedback control as exerted by the hormone thyroxine. Following surgical removal of the thyroid gland, the level of TSH in the blood will increase. Which of the following best explains this increase? A Residual blood thyroxine, from prior to thyroid gland removal, will bind to cells in the anterior pituitary, signaling more TSH secretion. B Thyroxine will remain bound to thyroxine receptors on various body cells, and these body cells will secrete additional hormones that stimulate the anterior pituitary to secrete TSH. C Thyroxine that was stored in the anterior pituitary prior to thyroid gland removal will signal more TSH secretion. D A decrease in thyroxine levels means a loss of inhibition to the hypothalamus and anterior pituitary, leading to increased TSH secretion.

If chemical signals in the cytoplasm control the progression of a cell to the M phase of the cell cycle, then fusion of a cell in G1 with a cell in early M phase would most likely result in the A replication of chromosomes only in the G1 cell B exiting of both cells from the cell cycle and into the G0 phase C condensation of chromatin in preparation of nuclear division in both cells D transfer of organelles from the G1 cell to the cell in the M phase

Cortisol is a hormone produced in response to stress, including starvation, in humans. Which of the following is most likely an immediate effect of a starvation-induced increase in cortisol secretion? A Increased activation of the immune system B Increased urine production by the kidneys C Increased bone and collagen formation D Increased mobilization of fatty acids from fat cells

Precise regulation of specific hormone levels is required for optimal sperm production in mammals, as summarized in the figure above. Anabolic-androgenic steroids (AAS) are synthetic variants of testosterone that are sometimes abused by persons who desire to enhance their athletic performance or alter their physique. Assuming that AAS function in the same way as naturally occurring testosterone, it is most likely that long-term abuse of AAS would A stimulate FSH secretion B stimulate testosterone production C stimulate LH secretion D reduce sperm production

Insulin, a hormone secreted by pancreatic cells, stimulates glucose uptake in skeletal muscle cells by mobilizing glucose transporter proteins (GLUT4) to the plasma membrane. As depicted in Figure 1, binding of insulin to the insulin receptor triggers an intracellular signaling cascade in which certain molecules activate other molecules in a relay of the hormone signal to cell targets. One outcome of the signaling cascade is mobilization of GLUT4 from vesicle storage sites in the cytoplasm to sites at the cell surface, where GLUT4 allows glucose to enter the cell. In type 2 diabetes, the cellular response to insulin is disrupted, and individuals with type 2 diabetes cannot properly regulate their blood glucose levels. In an investigation of the insulin signaling pathway, samples of skeletal muscle were isolated from individuals who have type 2 diabetes and from individuals who do not. The results of several experiments that were performed on the muscle samples are shown in Figure 2, Figure 3, and Figure 4. A The relatively low levels of glucose uptake in individuals with type 2 diabetes indicate that mobilization of GLUT4 to the cell surface is reduced in muscle cells of those individuals. B The relatively low levels of glucose uptake in individuals with type 2 diabetes indicate that no functional GLUT4 protein is produced in the muscle cells of those individuals. C The absence of activated insulin receptors in individuals with type 2 diabetes indicates that no insulin is secreted by the pancreatic cells of those individuals. D The absence of activated IRS-1 in individuals with type 2 diabetes indicates that no functional insulin receptor protein is produced in the muscle cells of those individuals.

Many human cells can be stimulated to divide by hormonelike growth factors that bind to receptor proteins (R) on the plasma membrane and trigger an internal signal-transduction cascade. In many cases, however, the process of contact inhibition prevents mitosis when cells are in direct contact with one another. Contact inhibition occurs when proteins called cell adhesion molecules (CAMs) interact, causing them to change shape so that the growth-factor signaling proteins that normally associate with CAMs are replaced by another protein, called M. Both pathways are depicted in the figures below. Which of the following statements accurately uses the information presented to support the hypothesis that interruption of M function in a single body cell can result in cancer? A Protein 3 will be prevented from interacting with CAMs, causing the cell cycle to stop permanently. B The ras protein will remain bound to DNA, blocking expression of genes required for mitosis. C Growth-factor signaling can trigger mitosis in cells that are in direct contact with other cells. D The receptor proteins of body cells will no longer bind to growth-factor proteins.

Based on the model of eukaryotic cell cycle regulation shown in the figure, which of the following best describes the effect of a drug that blocks the production of the mitotic cyclin? A The cell cycle would proceed uncontrollably, and the cell would become cancerous. B The G1 cyclin would functionally replace mitotic cyclin, and the cell would continue dividing normally. C DNA synthesis would be prevented, and the cell would stop dividing. D The cell would be prevented from entering mitosis, and the cell would stop dividing.

The mechanism of action of many common medications involves interfering with the normal pathways that cells use to respond to hormone signals. Which of the following best describes a drug interaction that directly interferes with a signal transduction pathway? A A medication causes the cell to absorb more of a particular mineral, eventually poisoning the cell. B A medication enters the target cell and inhibits an enzyme that normally synthesizes a second messenger. C A medication enters the target cell's nucleus and acts as a mutagen. D A medication interrupts the transcription of ribosomal RNA genes.

Steroid hormones, such as testosterone, pass through the plasma membrane and bind to an intracellular protein, as shown in the diagram below. The hormone-receptor complex then enters the nucleus, where it interacts with DNA to promote transcription of a specific gene. A Histone protein synthesis will increase because histones maintain the DNA in an optimal conformation for chromosome assembly. B Ribosome production will increase because ribosomes are specific for the mRNA with which they bind during translation. C DNA replication will increase as a result of the binding of the hormone-receptor complex to the DNA. D Production of a specific mRNA will increase as a result of the binding of the hormone-receptor complex to the DNA.

The graph above shows changes in glucagon and insulin secretions at different concentrations of blood glucose. Which of the following feedback mechanisms is best supported by the data? A A falling glucagon level causes a rise in the insulin level, which maintains equal amounts of both hormones in the blood. B A high glucagon level causes a rise in the insulin level, which maintains high levels of both hormones in the blood. C A low glucose level causes the release of glucagon, which stimulates the release of more glucose from tissues, which in turn lowers the amount of glucagon being released. D A low glucose level causes the release of insulin, which stimulates the release of more glucose from tissues, which in turn increases the amount of insulin being released.

Two types of cholesterol transport proteins, low-density lipoproteins (LDL) and high-density lipoproteins (HDL), bind to cholesterol and carry it through the bloodstream. Familial hypercholesterolemia (FH) is characterized by high cholesterol levels in the blood, which can lead to cardiovascular disease. FH is associated with a loss-of-function mutation of a gene that encodes LDL receptors in liver cells. Individuals who are heterozygous produce lower-than-normal amounts of the LDL receptors, and individuals who are homozygous for the mutant allele have no LDL receptor function. Individuals with FH can be treated with drugs that result in increased production of LDL receptors in liver cells. Which of the following best explains the observation that the drugs can effectively control blood cholesterol levels in individuals who are heterozygous but are not effective in individuals homozygous for the mutant allele? A The drugs repair the mutant allele by copying the wild-type allele. B The drugs prevent cholesterol from entering the liver cells in individuals who are heterozygous but not in individuals who are homozygous for the mutant allele. C Cholesterol molecules primarily bind to HDL receptors in individuals with FH. D There must be at least one copy of the wild-type LDL receptor allele to produce functional LDL receptors.