AP Biology Unit 4
Based on Table 1, what percent of the life cycle of yeast cells is spent in DNA replication?
25 %
Which of the following outcomes will most likely result from the irreversible binding of GDP to the G protein?
The intracellular concentration of glycogen will increase.
The cell cycle of yeast cells grown in the nutrient-poor environment is approximately what percent of the cell cycle of yeast cells grown in the nutrient-rich environment?
168
Based on the data, the percent of the mitotic cells that were in metaphase is closest to which of the following?
18%
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 defect in a cell-cycle checkpoint prevents a cell from entering the S phase.
Which of the following steps in a signaling pathway typically occurs first once a chemical messenger reaches a target cell?
A ligand binds to a receptor.
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 medication enters the target cell and inhibits an enzyme that normally synthesizes a second messenger.
Which of the following best describes the production of DMSP by coral and coral symbionts?
A negative feedback mechanism that reverses the environmental change
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?
ADH promotes an increase in the movement of water into the bloodstream.
Damaged tissue releases chemicals that activate platelets and stimulate the formation of blood clots. Which of the following predictions about the activity of platelets best describes a positive feedback mechanism?
Activated platelets release chemicals that activate more platelets.
The endocrine system incorporates feedback mechanisms that maintain homeostasis. Which of the following demonstrates negative feedback by the endocrine system?
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.
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−9ced−9 and ced−3ced−3 . The ced−3ced−3 gene was found to promote cell death, and ced−9ced−9 to inhibit it. The ced−9ced−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−9ced−9 in C. elegans can affect regulation of apoptosis in the cell?
An experiment showed that a mutation in the ced−9ced−9 gene led to excessive cell death in C. elegans.
Based on the model of ferritin synthesis presented in Figure 2, which of the following describes the role of feedback on the control of intracellular iron levels?
An increase in iron levels activates synthesis of ferritin protein. Ferritin protein in turn binds iron, thereby decreasing both free iron levels and ferritin synthesis.
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?
Calcitonin levels will rise, thus promoting the deposit of calcium into bones.
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?
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.
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?
Chemicals that are secreted from antigen-presenting cells then activate helper T cells.
Figure 1 shows the number of chromosomes observed in an actively dividing human cell at each stage of cell division. Which of the following presents a correct interpretation of the changes in chromosome number depicted in Figure 1 ?
Chromosomes enter metaphase containing two chromatids attached by a centromere. During anaphase, the chromatids are separated, each becoming a chromosome. Cytokinesis distributes the chromosomes into two separate cells.
Two types of cells, alpha and beta cells, produce signaling molecules that affect blood sugar levels in opposite ways (Figure 1). Epinephrine is a chemical, often released during periods of exercise, that ultimately causes an increase in blood sugar levels in the body. Based on Figure 1, which of the following best explains how exercise causes blood glucose levels to rise?
Epinephrine activates alpha cells, causing the release of glucagon, and inhibits beta cells, blocking the release of insulin.
The EspEsp gene encodes a protein that alters the structure of the insulin receptor on osteoblasts and interferes with the binding of insulin to the receptor. A researcher created a group of osteoblasts with an EspEsp mutation that prevented the production of a functional EspEsp product (mutant). The researcher then exposed the mutant strain and a normal strain that expresses EspEsp to glucose and compared the levels of insulin in the blood near the osteoblasts (Figure 2). Which of the following claims is most consistent with the data shown in Figure 2 ?
Esp expression is necessary to prevent the overproduction of insulin.
Figure 1 shows a model of the endocrine signaling pathway that regulates ovulation. Which of the following observations would provide evidence of a positive feedback mechanism in this system?
Estrogen from the ovaries stimulates the hypothalamus and anterior pituitary to secrete more GnRH, LH, and FSH.
Warfarin is a drug used to treat certain blood clots. Warfarin blocks the formation of the active form of vitamin KK-dependent clotting factors. Based on the model, which of the following best predicts the effects of warfarin on a patient?
Factor X will not be activated, which will prevent thrombin from forming.
Based on the experimental results, which of the following describes the most likely defect in muscle cells of patients with type 2 diabetes?
IRS-1 activation is reduced at high insulin concentrations.
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 SRYSRY 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?
If the SRYSRY gene is absent or nonfunctional, the embryo will exhibit female sexual development.
Which of the following best predicts what will happen to the blood glucose level if the person has another meal at 5 p.m.?
Immediately after the meal, the blood glucose level will increase, and then insulin will be secreted to counter the increase.
Based on Figure 1, which of the following statements best describes the epinephrine signaling pathway?
In involves enzymes activating other enzymes.
Researchers performed an experiment to determine the effect of certain genetic mutations on mitosis in tropical fruit fly embryos. They determined the percentage of cells in each of four phases of mitosis as shown in Figure 1. Which of the following patterns is shown by the data?
In mutant 3 cells, more time is spent in prophase/prometaphase than in the later stages of mitosis.
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?
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 .
The epidermal growth factor receptor EGFREGFR is a cell surface receptor. When a growth factor binds to EGFREGFR, the receptor is activated. The activated EGFREGFR 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 EGFREGFR to be active in the absence of a growth factor?
Increased cell division will lead to the formation of a tumor.
Based on the data, which of the following best represents how the mice with the implanted hESC-β cells use negative feedback to return blood glucose levels to normal if blood glucose levels increase?
Increased insulin secretion by hESC-β cells → increased glucose uptake by body cells → decreased insulin secretion by hESC-β cells
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?
Increased mobilization of fatty acids from fat cells
Which of the following best describes the effect of insulin binding to the receptor on the osteoblast cells?
Insulin binding ultimately increases pancreatic secretion of additional insulin.
Which of the following statements best describes the role of adenylyl cyclase in the epinephrine signaling pathway?
It accelerates the production of a second messenger.
Ethylene causes fruits to ripen. In a signaling pathway, receptors activate transcription factors, which ultimately leads to ripening. Which of the following best supports the claim that ethylene initiates the signal transduction pathway that leads to ripening of fruit?
Loss-of-function mutations in ethylene receptors result in changes to the ripening process.
Based on Figure 2, which of the following best supports the claim that drug X inhibits oxygen consumption?
Melanoma line 3 consumes statistically less oxygen per cell in the presence of drug X than it does in the presence of the solvent alone.
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?
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.
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?
Negative feedback regulation does not occur, so the enzyme will be active when glycolysis is not needed.
Cyclic =AMP phosphodiesterase is an enzyme that catalyzes the conversion of cyclic AMP to a different molecule. Which of the following best predicts the effect of inhibiting cyclic AMP phosphodiesterase in a muscle cell stimulated by epinephrine?
Phosphorylase kinase will remain active because protein kinase A will no longer be deactivated.
Which of the following most accurately describes an observation and an effect of the viral infection indicated by the data in Table 1?
Seventy-five percent of the virus-infected cells are found in mitosis. The virus stimulates frequent cell division.
Based on Figure 1, which of the following statements correctly links a stage of the cell cycle with the event occurring at that stage?
Synthesis of sufficient DNA for two daughter cells occurs in stage II.
Which of the following best describes how the amount of DNADNA in the cell changes during MM phase?
The amount of DNADNA is halved as the cell divides into two daughter cells.
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?
The cell would be prevented from entering mitosis, and the cell would stop dividing.
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?
The feedback mechanism would maintain relatively constant levels of thyroxin throughout tissue targets.
Which of the following statements best predicts the effect of a mutation that results in a loss of the glucocorticoid receptor's ligand binding function?
The glucocorticoid receptor will remain associated with the accessory proteins.
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?
The hormone is released into the bloodstream where it can be transported to all cells with the correct receptors.
Which of the following changes in the FGFR signaling pathway is most likely to result in uncontrolled cell proliferation?
The irreversible association of FGFR proteins
Which of the following best explains how small molecules move between adjacent cells in a plant shoot?
The molecules pass freely through plasmodesmata, which are cytoplasmic strands connecting two cells.
Based on the information provided, which of the following best justifies the claim that osteocalcin is a hormone?
The osteoblasts in the bone secrete osteocalcin, which causes cells in the pancreas to change their activity.
Vertebrate immune responses involve communication over short and long distances. Which of the following statements best helps explain how cell surface proteins, such as MHCMHC proteins and T cell receptors, mediate cell communication over short distances?
The proteins interact directly with proteins on the surfaces of other cells.
Which of the following outcomes will most likely result from the inactivation of the beta-2 adrenergic receptor?
The rate of glycogen synthesis in the cell will increase.
Figure 1. Accumulation of acetyl-CoACoA under different conditions Which of the following observations provides the best evidence that acetyl-CoACoA negatively regulates pyruvate dehydrogenase activity?
The rate of the pyruvate dehydrogenase-catalyzed reaction is slower in the presence of a higher concentration of acetyl-CoACoA.
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. Which of the following is a valid interpretation of the experimental results that explains how individuals with type 2 diabetes differ from individuals without diabetes?
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.
Which of the following statements best predicts the effect of a loss of function of the insulin receptor's intracellular domain?
The storage of GLUT4 in vesicles inside the cell will increase.
Which of the following best describes the scientists' findings concerning the density of symbionts presented in Figure 2 ?
The symbiont density at32°C was different from the density at 27°C on days 55 and 1010 of the experiment.
Which statement best predicts why a cell's progression through the cell cycle might be halted at the G1G1/SS checkpoint?
There are not enough nucleotides available to construct new DNA.
Figure 1. Amount of DNADNA in picograms per cell over several rounds of cell division Which of the following statements is consistent with the data in Figure 1?
There is a change from 3 to 6 picograms of DNADNA because DNA is replicated before each round of cell division.
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?
They allow the movement of molecules from one cell to another, enabling communication between cells.
The tumor suppressor protein p53p53 binds to DNA and activates target genes, which results in the synthesis of p21p21, CD95CD95, and other proteins. The p21p21 protein promotes cell-cycle arrest, whereas the CD95CD95 protein promotes apoptosis. Which of the following will most likely result from a loss of p53 function?
Uncontrolled cell proliferation
GG 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?
cAMPcAMP results in the activation of an enzyme that amplifies the signal by acting on many substrate molecules.
