AP Bio MCQ Exam 4
An antigen can induce an immune response in a host organism. Antigens are targeted by antibodies that are produced by the organism's immune system in response to contact with the antigen. Antibodies are specific to antigens. Many different cell types are involved in immune responses. Which of the following best describes the role of cell-to-cell communication during a response to an invasion of antigens? A Chemicals that are secreted from antigen-presenting cells then activate helper T cells. B A macrophage cell engulfs a pathogen in the blood. C Antigens attaching to receptors on memory B cells stimulate the memory B cells to become plasma cells. D Antigen-presenting cells engulf antigens at the first exposure.
Answer A Correct. Cell signaling pathways are activated by cell-to-cell communication.
Metformin is a drug used to treat type 2 diabetes by decreasing glucose production in the liver. AMP-activated protein kinase (AMPK) is a major cellular regulator of glucose metabolism. Metformin activates AMPK in liver cells but cannot cross the plasma membrane. By blocking AMPK with an inhibitor, researchers found that AMPK activation is required for metformin to produce an inhibitory effect on glucose production by liver cells. Which of the following best describes the component that metformin represents in a signal transduction pathway that regulates glucose production in the liver? A It is a secondary messenger that amplifies a signal through a cascade reaction. B It is a ligand that activates the signal transduction pathway of the activation of AMPKAMPK. C It is an allosteric regulator that binds to a crucial section of the DNADNA that makes the enzymes needed for glucose uptake. D It is a competitive inhibitor that binds to glucose and prevents it from entering the cell.
Answer B Correct. Since metformin does not cross the membrane, it is likely a ligand that binds to a receptor on the surface of the plasma membrane, initiating the signal transduction pathway.
The relative amounts of DNA present in the nucleus of a cell at four different stages of the life cycle are shown in Figure 1. Figure 1. Relative amounts of DNA present in the nucleus of a cell Based on Figure 1, which of the following statements correctly links a stage of the cell cycle with the event occurring at that stage? A Stage II represents the G2G2 phase of the cell cycle. B Synthesis of sufficient DNADNA for two daughter cells occurs in stage IIII. C Stage IIIIII includes mitosis. D The replication of genetic material occurs in stage IVIV.
Answer B Correct. Stage IIII represents the SS (synthesis) phase of interphase. The genetic information (DNADNA) is doubling. If this did not occur, the daughter cells formed as a result of the cell cycle would have too little genetic information (chromosomes). This process is visible on the graph, as the copies of genetic information increase from one to two copies.
The tumor suppressor protein p53 binds to DNA and activates target genes, which results in the synthesis of p21, CD95, and other proteins. The p21 protein promotes cell-cycle arrest, whereas the CD95 protein promotes apoptosis. Which of the following will most likely result from a loss of p53 function? A Rapid cell growth without cell division B Immediate activation of apoptosis pathways C Uncontrolled cell proliferation D Increased expression of p53p53 target genes
Answer C Correct. A loss of p53p53 function will result in unregulated cell proliferation because the p21p21 protein will not be synthesized. In the absence of the p21p21 protein, a cell will continue to progress through the cell cycle without stopping.
Which of the following steps in a signaling pathway typically occurs first once a chemical messenger reaches a target cell? A Specific genes are activated. B A second messenger molecule is produced. C A ligand binds to a receptor. D Specific proteins are synthesized.
Answer C Correct. The chemical messenger (ligand) first binds to a receptor, which then changes shape to initiate the signaling pathway.
A student used microscopy to investigate the relative lengths of the different stages of mitosis. The student prepared slides of cells isolated from a growing onion root tip and viewed the slides under a dissecting microscope. The student then made diagrams of cells that were in different stages of mitosis and counted the number of cells that were in each of those stages. The student's data are presented in Table 1. Table 1. Number of cells in each of four different stages of mitosis Based on the data, the percent of the mitotic cells that were in metaphase is closest to which of the following? A 5% B 11% C 18% D 66%
Answer C Correct. The number of cells that were in metaphase equals 7, and the total number of mitotic cells equals 38. The percent of mitotic cells in metaphase is calculated as follows: divide 7 by 38 and multiply by 100. The correct answer is 18 percent.
A model of the typical life cycle of a cell is shown in Figure 1. Figure 1. Typical life cycle of a eukaryotic cell Scientists have estimated that it takes yeast cells approximately 20 hours to complete the entire cycle. Table 1 shows the amount of time in each phase of the life cycle for yeast cells. Table 1. Amount of time spent in each stage of the cell cycle by yeast cells StageMG1SG2Time (hours)21053 Based on Table 1, what percent of the life cycle of yeast cells is spent in DNA replication? A 5 percent B 10 percent C 25 percent D 50 percent
Answer C Correct. The yeast cells spend 5 hours out of a total of 20 hours in SS phase, which is 25%
Researchers grew seedlings of corn, Zea mays, in loose and compact sand. The researchers measured the amount of time required for the cells in the growing root tips of the seedlings to double in number. The mean cell doubling times for the two groups of seedlings are shown in Figure 1. Figure 1. Mean cell doubling times for the growing root tips of Zea mays seedlings planted in loose or compact sand Based on the sample means, which of the following conclusions about the cells in the growing root tips of Zea mays seedlings is best supported by the results of the experiment? A The cells of the root tips grow to larger sizes when the seedlings are planted in compact sand than when the seedlings are planted in loose sand. B The average rate of mitotic cell division is greater for the root tips growing in loose sand than for the root tips growing in compact sand. C The average cell cycle time is greater for the root tips growing in compact sand than for the root tips growing in loose sand. D More cells are produced per unit of time in the root tips growing in compact sand than in the root tips growing in loose sand.
Answer D Correct. According to the figure, the mean cell doubling time of Zea mays seedling root tips in compact sand is less than in loose sand. A lower mean cell doubling time indicates an increased rate of mitotic cell division for cells of root tips in compact sand.
During a fight-or-flight response, epinephrine is released into the body's circulatory system and transported throughout the body. Some cells exhibit a response to the epinephrine while other cells do not. Which of the following justifies the claim that differences in components of cell signaling pathways explain the different responses to epinephrine? A Cell signaling depends on the ability to detect a signal molecule. Not all cells have receptors for epinephrine. Only cells with such receptors are capable of responding. B Cell signaling depends on the transduction of a received signal by the nervous system. Not all cells are close enough to a synapse to receive the signal and respond. C Cell signaling depends on the signal being able to diffuse through the cell membrane. Epinephrine is incapable of diffusing through some plasma membranes because of the membrane's phospholipid composition. D Cell signaling requires reception, transduction, and response. All cells can receive epinephrine, all cells respond with a pathway, but only select cells have the proper coding in their DNADNA to respond.
Answer A Correct. Cell signaling starts with the reception of the signal. Not all cells are equipped to receive all signals. Only those cells with the correct receptor to a signal will be able to respond to a signal such as epinephrine.
Researchers have discovered details about apoptosis (programmed cell death) by studying embryologic development of a nematode worm, Caenorhabditis elegans. Apoptosis is a normal developmental process in C. elegans. They found several genes involved in apoptosis, including ced−9 and ced−3 . The ced−3 gene was found to promote cell death, and ced−9 to inhibit it. The ced−9 gene serves as a regulator that prevents apoptosis in the absence of a signal promoting apoptosis. Which of the following statements best justifies the claim that changes in the expression of ced−9 in C. elegans can affect regulation of apoptosis in the cell? A An experiment showed that a mutation in the ced−9ced−9 gene led to excessive cell death in C. elegans. B An experiment showed that the ced−9ced−9 gene normally produces a protein that promotes excessive cell death in C. elegans. C A mutation in ced−3ced−3 will cause ced−9ced−9 to be incorrectly transcribed. D Apoptosis is dependent on a signal from the ced−9ced−9 gene in C. elegans.
Answer A Correct. If ced−9ced−9 acts as a regulator and normally inhibits apoptosis, then if it loses function, more cell death will occur.
Adjacent plant cells have narrow channels called plasmodesmata that pass through the cell walls of the connected cells and allow a cytoplasmic connection between the cells. Which of the following statements best describes a primary function of plasmodesmata? A They allow the movement of molecules from one cell to another, enabling communication between cells. B They prevent the cell membrane from pulling away from the cell wall during periods of drought. C They eliminate the need to produce signaling molecules and eliminate the need for cells to have receptors for signaling molecules. D They increase the surface area available for attachment of ribosomes and thus increase protein synthesis.
Answer A Correct. Plasmodesmata are channels through which cytosol exchange can occur, moving select molecules directly between cells. This enables cells enclosed by a cell wall to communicate.
Fibroblast growth factor receptors (FGFRs) are transmembrane proteins that regulate cellular processes such as cell proliferation and differentiation. The extracellular domains of FGFR proteins bind specifically to signaling molecules called fibroblast growth factors. The intracellular domains of FGFR proteins function as protein kinases, enzymes that transfer phosphate groups from ATP to protein substrates. FGFR activation occurs when binding by fibroblast growth factors causes FGFR proteins in the plasma membrane to become closely associated with each other. The association of two FGFR proteins stimulates protein kinase activity, which triggers the activation of intracellular signaling pathways. A simplified model of FGFR activation is represented in Figure 1. Figure 1. A simplified model of FGFR activation Which of the following changes in the FGFR signaling pathway is most likely to result in uncontrolled cell proliferation? A The irreversible association of FGFRFGFR proteins B The loss of the FGFRFGFR protein kinase function C A decrease in the intracellular concentration of ATPATP D A decrease in the extracellular concentrations of fibroblast growth factors
Answer A Correct. The irreversible association of FGFRFGFR proteins will most likely result in the permanent activation of the FGFRFGFR signaling pathway. Because the FGFRFGFR signaling pathway regulates cell proliferation, the irreversible association of FGFRFGFR proteins will result in uncontrolled cell proliferation.
Figure 1 represents the relative time and sequence of the phases of the cell cycle. Figure 1. Representation of the cell cycle and identification of the G1/S checkpoint Which statement best predicts why a cell's progression through the cell cycle might be halted at the G1/S checkpoint? A Spindle fibers have not correctly attached to chromosomes. B There are not enough nucleotides available to construct new DNADNA. C Damage occurred to DNADNA when it was being copied in G1G1. D Proteins necessary for MM phase of the cell cycle have not been produced.
Answer B Correct. DNADNA replication, which occurs during SS phase, requires free nucleotides. If nucleotides are unavailable, the G1G1/SS checkpoint halts the cell cycle to conserve energy.
The epidermal growth factor receptor EGFR is a cell surface receptor. When a growth factor binds to EGFR, the receptor is activated. The activated EGFR triggers a signal transduction pathway, which leads to increased frequency of cell division. Which of the following best predicts the effect of a mutation that causes EGFR to be active in the absence of a growth factor? A Increased apoptosis will lead to abnormal growth of the tissue. B Increased cell division will lead to the formation of a tumor. C Cells will exit the cell cycle, entering a non-dividing G0G0 phase. D Fewer cells will be in any of the stages of mitosis.
Answer B Correct. Growth factors are important signaling molecules that trigger cells to divide at the correct rate and correct time. An EGFREGFR that is active when a growth factor is absent would lead to increased cell division. Uncontrolled cell growth will likely result in a tumor.
Signal transduction may result in changes in gene expression and cell function, which may alter phenotype in an embryo. An example is the expression of the SRY gene, which triggers the male sexual development pathway in mammals. This gene is found on the Y chromosome. Which statement provides the evidence to justify the claim that signal transduction may result in an altered phenotype? A If the SRYSRY gene is absent or nonfunctional, the embryo will exhibit male sexual development. B If the SRYSRY gene is absent or nonfunctional, the embryo will exhibit female sexual development. C An embryo with a male sex chromosome will always exhibit male sexual development. D An embryo with two male sex chromosomes will always exhibit male sexual development.
Answer B Correct. The SRYSRY gene must be present and functional for normal male sexual development. It is the proper functioning of the SRYSRY gene that is important, and this is the best statement to support the claim
A person's blood glucose level fluctuates during the day, as represented in Figure 1. Two hormones, insulin and glucagon, are directly involved in regulating the blood glucose level to maintain a healthy level. Insulin acts to lower the blood glucose level, and glucagon acts to increase the blood glucose level. Figure 1. Blood glucose fluctuations of an individual Which of the following best predicts what will happen to the blood glucose level if the person has another meal at 5 p.m.? A Immediately after the meal, the blood glucose level will decrease because of the increase in glucagon levels. B Immediately after the meal, the blood glucose level will increase, and then insulin will be secreted to counter the increase. C Several hours after the meal, the blood glucose level will increase sharply because of an increase in the amount of glucagon secreted. D The blood glucose level will not change after the 5 p.m. meal because the person has already consumed two meals and the blood glucose level has been adjusted to a steady-state level.
Answer B Correct. The blood glucose levels increase due to the nutrients taken in. This increase is a signal for the pancreas to release more insulin that will stimulate cells to take in the excess glucose. As a result, the blood glucose level will then decrease.
The insulin receptor is a transmembrane protein that plays a role in the regulation of glucose homeostasis. The receptor's extracellular domain binds specifically to the peptide hormone insulin. The receptor's intracellular domain interacts with cellular factors. The binding of insulin to the receptor stimulates a signal transduction pathway that results in the subcellular translocation of GLUT4, a glucose transport protein that is stored in vesicles inside the cell. A simplified model of the insulin receptor-signaling pathway is shown in Figure 1. Figure 1. A simplified model of the insulin receptor-signaling pathway Which of the following statements best predicts the effect of a loss of function of the insulin receptor's intracellular domain? A The stimulation of the signal transduction pathway will increase. B The storage of GLUT4GLUT4 in vesicles inside the cell will increase. C The number of GLUT4GLUT4 molecules in the plasma membrane will increase. D The concentration of glucose inside the cell will increase.
Answer B Correct. The insulin receptor's intracellular domain is required for the stimulation of the signal transduction pathway. If the signal transduction pathway is not stimulated by the insulin receptor, the GLUT4GLUT4 vesicles will not be translocated to the plasma membrane. Consequently, the storage of GLUT4GLUT4 in vesicles inside the cell will increase.
Phosphofructokinase (PFK) is a key enzyme in glycolysis. ATP is one of the two substrates for the reaction catalyzed by PFK. ATP is also an allosteric regulator of PFK. Figure 1 shows the enzyme-substrate interactions of PFK. Figure 1. The enzyme-substrate interactions of PFK A researcher found a mutation that resulted in the PFK enzyme being unable to bind ATP to the allosteric site. Which of the following best predicts the effect of the mutation? A The activity of the enzyme will not be affected because the active site is not involved in substrate binding at the allosteric site. B Negative feedback regulation does not occur, so the enzyme will be active when glycolysis is not needed. C Positive feedback does not occur, and the activity of the enzyme will decrease when glycolysis is needed. D The activity of the enzyme will fluctuate independent of the ATPATP concentration.
Answer B Correct. The reaction is normally inhibited when ATPATP binds to the allosteric site and changes the shape of the active site to the point where it can no longer bind to the substrate. The mutation will not allow this inhibition to occur, and the enzyme will be active even at high ATPATP concentrations.
A hydrophilic peptide hormone is produced in the anterior pituitary gland located at the base of the brain. The hormone targets specific cells in many parts of the body. Which of the following best explains a possible mechanism that would enable the hormone to efficiently reach all of the target cells in the body? A The hormone interacts with the nerves at the base of the brain and directs signals to the target cells through the nervous system. B The hormone diffuses into target cells adjacent to the anterior pituitary gland, where the hormone is degraded. C The hormone is released into the bloodstream where it can be transported to all cells with the correct receptors. D The hormone moves through cytoplasmic connections between cells until it has reached all cells with the correct intracellular binding sites.
Answer C Correct. The bloodstream is the most effective way to distribute a hormone that has to reach multiple target cells that are relatively long distances from the source of the hormone.
Researchers tracked the amount of DNA (measured in picograms) over time beginning with a single cell and continuing through several rounds of cell division. The researchers observed threadlike chromosomes prior to cell division. The threadlike chromosomes disappeared from view shortly after each division. The amount of DNA in picograms per cell over several rounds of cell division is shown in Figure 1. Figure 1. Amount of DNA in picograms per cell over several rounds of cell division Which of the following statements is consistent with the data in Figure 1? A The cells have a haploid chromosome number of 3. B The cells have a diploid chromosome number of 6. C There is a change from 3 to 6 picograms of DNADNA because DNADNA is replicated before each round of cell division. D There is a change from 6 to 3 picograms of DNADNA after each cell division because the chromosomes lengthen following cell division.
Answer C Correct. The change from 3 to 6 picograms of DNADNA prior to replication indicates that the DNADNA has been replicated. The replicated DNADNA is condensed into chromosomes during cell division or mitosis. This ensures that the complete genome from a parent cell is passed on to two genetically identical daughter cells.
The beta-2 adrenergic receptor is a membrane-bound protein that regulates several cellular processes, including the synthesis and breakdown of glycogen. The receptor binds specifically to the hormone epinephrine. The binding of epinephrine to the beta-2 adrenergic receptor triggers a signal transduction cascade that controls glycogen synthesis and breakdown in the cell. A simplified model of the signal transduction cascade is represented in Figure 1. Figure 1. A simplified model of the signal transduction cascade triggered by epinephrine binding to the beta-2 adrenergic receptor Which of the following outcomes will most likely result from the inactivation of the beta-2 adrenergic receptor? A The cellular concentration of cyclic AMPAMP will increase. B The enzymatic activity of protein kinase A will increase. C The activation of glycogen phosphorylase will increase. D The rate of glycogen synthesis in the cell will increase.
Answer D Correct. Based on Figure 1, activation of the beta-2 adrenergic receptor results in the stimulation of glycogen breakdown and the inhibition of glycogen synthesis. The immediate effect of inactivating the beta-2 adrenergic receptor will be an increase in the rate of glycogen synthesis in the cell because glycogen synthase will no longer be inhibited. Also, glycogen breakdown in the cell will no longer be stimulated because glycogen phosphorylase will most likely be deactivate
A cell culture commonly used in research was selected to study the effect of a specific virus on the timing of cell cycle phases. Two separate cultures were started, one untreated and one inoculated with the virus. Both cultures were incubated under identical conditions. After a period of time, 200 cells from each culture were observed and classified as shown in Table 1. Table 1. Number of normal and infected cells found in three phases of the cell cycle Phase of Cell CycleUntreated Cells (n=200)Virus-Infected Cells (n=200)G019610Interphase240Mitosis2150 Which of the following most accurately describes an observation and an effect of the viral infection indicated by the data in Table 1? A Normal cells spend 98 percent of their time cycling in and out of interphase. The virus reduces this to 5 percent of the time. B Twenty percent of the virus-infected cells are in interphase. These cells are no longer part of the cell cycle. C Forty percent of the virus-infected cells are in interphase. These cells are preparing for replication of genetic material. D Seventy-five percent of the virus-infected cells are found in mitosis. The virus stimulates frequent cell division.
Answer D Correct. One hundred fifty out of 200 is 75 percent. The virus activates cells currently in the G0G0 phase, leading to rapid cell growth and division.
G proteins are a family of receptor proteins that are involved in transmitting signals from outside a cell to inside a cell. When a signaling molecule binds to a G protein, the G protein is activated. The G protein then activates an enzyme that produces a second messenger called cAMP. Which of the following describes a critical role of cAMP during the transduction stage of a G protein signal transduction pathway? A cAMPcAMP carries the signal to the nucleus of the cell and results in new sequences of nucleotides being added to the cell's DNADNA. B cAMPcAMP binds the extracellular signal molecule and carries it to the intracellular target specified by the signal. C cAMPcAMP modifies a specific monomer so that it can be added to an elongating structural macromolecule. D cAMPcAMP results in the activation of an enzyme that amplifies the signal by acting on many substrate molecules.
Answer D Correct. Typically, cAMPcAMP immediately activates protein kinase AA, which phosphorylates various other proteins. Kinases are a type of enzyme that activates proteins by transferring a phosphate group from ATPATP. Kinases are involved in many signaling pathways in a wide variety of organisms.
Blood clots are formed by a positive feedback loop. Two pathways exist, the extrinsic and intrinsic pathways, which converge during clot formation. There are many clotting factors involved, most of which are proteins. Vitamin K is required for the formation of the active form of several of the clotting factors, including Factor X. A simplified model of the blood clotting process is shown in Figure 1. Figure 1. Simplified model of clotting cascade Warfarin is a drug used to treat certain blood clots. Warfarin blocks the formation of the active form of vitamin K-dependent clotting factors. Based on the model, which of the following best predicts the effects of warfarin on a patient? A Fibrinogen will form fibrin, but the clot will not form because Factor XIIIXIII will not be synthesized. B The intrinsic pathway will take over because the clotting factors are part of that pathway. C Thrombin will be converted to prothrombin because Factor XX will reverse the reaction. D Factor XX will not be activated, which will prevent thrombin from forming.
Answer D Correct. Vitamin KK is required for the synthesis of Factor XX and warfarin inhibits that process; thus, clots are prevented from forming.