ap bio unit four

A researcher observes that mice from the mutant strain experience low blood sugar. Which of the following best describes the feedback mechanism in the pathway (Figure 1) causing the low blood sugar in the mutant strain? A The positive feedback of insulin production B The negative feedback of inactive osteocalcin production C The positive feedback of the EspEsp protein D The negative feedback of insulin-secreting pancreatic cell proliferation

A

Based on the information presented, which of the following genetic changes in an individual without diabetes is most likely to result in a disrupted cellular response to insulin signaling similar to that of an individual with type 2 diabetes? A A deletion in the gene encoding the insulin receptor that removes only the cytoplasmic domain of the protein B Duplication of the gene encoding a PI-3 kinase that results in synthesis of a muscle-specific variant of the enzyme in skin cells as well as in muscle cells C A mutation in the gene encoding IRS-1 that causes the protein to be active in muscle cells even in the absence of insulin signaling D Insertion of a small segment of DNA into the promoter of the Glut4 gene that results in increased synthesis of GLUT4 proteins in muscle cells

A

Based on the information provided, which of the following best describes the role of insulin in this liver cell signal transduction pathway? A It acts as a ligand. B It acts as a receptor. C It acts as a secondary messenger. D It acts as a protein kinase.

A

DNA replication occurs A during the S phase of the cell cycle B as the nuclear envelope breaks down in early mitosis C during mitosis but not during meiosis D in animal cells but not in plant cells E only in cells destined to become gametes

A

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.

A

Ethylene gas is an organic molecule that serves many cell signaling roles in flowering plants. Which of the following best explains how a positive feedback mechanism involving ethylene works? A Cells of ripening fruit produce ethylene, which activates the ripening response in other fruit cells. B Low water stress causes cells to produce ethylene, which binds to root cells and initiates cell division. C Cells damaged by leaf-eating insects produce ethylene, which is released into the air, and repels insects. D Fertilized ovules produce ethylene, which initiates apoptosis in flower petal cells.

A

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? A 168 B 127 C 179 D 160

A

Which of the following best describes the effect of insulin binding to the receptor on the osteoblast cells? A Insulin binding ultimately increases pancreatic secretion of additional insulin. B Insulin binding blocks the release of osteocalcin from the osteoblasts. C Insulin binding inhibits the expression of EspEsp. D Insulin binding increases the pHpH of the extracellular matrix.

A

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

A

Which of the following best explains the feedback mechanism illustrated in Figure 1 ? A This is an example of positive feedback, because the few platelets that initially bind attract more platelets to the damaged area. B This is an example of positive feedback, because it results from the interactions among collagen, endothelial cells, and platelets. C This is an example of negative feedback, because a large clump of platelets can block the blood vessel and prevent blood flow through it. D This is an example of negative feedback, because the accumulation of platelets returns the open blood vessel wall to a closed state.

A

Which of the following best predicts how GSK3βGSK3β mutations can lead to the development of cancer? A Cells with inactive GSK3βGSK3β fail to trigger apoptosis. B Cells with inactive GSK3βGSK3β fail to proceed past the G2/MG2/M checkpoint. C Cells with overactive GSK3βGSK3β are more likely to repair DNADNA damage. D Cells with overactive GSK3βGSK3β have longer cell cycles.

A

Which of the following claims is most consistent with the data shown in Figure 2 ? A EspEsp expression is necessary to prevent the overproduction of insulin. B EspEsp protein does not regulate blood-sugar levels in normal mice. C Normal mice require a higher blood concentration of insulin than mutant mice do. D Mutant mice have a cyclical pattern of insulin secretion.

A

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? 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.

A

Which of the following observations provides the best evidence that acetyl-CoACoA negatively regulates pyruvate dehydrogenase activity? A) The rate of the pyruvate dehydrogenase-catalyzed reaction is slower in the presence of a higher concentration of acetyl-CoACoA. B) The gene that encodes pyruvate dehydrogenase is transcribed when excess acetyl-CoACoA is detected. C) The accumulation of acetyl-CoACoA stops after 7070 seconds, regardless of the reaction mixture. D) Acetyl-CoACoA is continuously broken down in the Krebs cycle.

A

Which of the following outcomes will most likely result from the irreversible binding of GDPGDP to the G protein? A The intracellular concentration of glycogen will increase. B The intracellular concentration of activated protein kinase A will increase. C The intracellular concentration of cyclic AMPAMP will increase. D The intracellular concentration of glucose-1-phosphate will increase.

A

Which of the following provides correct information about cell signaling that supports the claim? A The SRYSRY gene produces a protein that binds to specific regions of DNADNA in certain tissues, which affects the development of these tissues. B The SRYSRY gene produces a protein that deletes portions of the XX chromosome in males so that male characteristics can develop. C The SRYSRY gene produces an RNARNA segment that is exported from specific cells and targets the developing gonads. D The SRYSRY gene is found only in tissues of the developing gonads.

A

Which of the following research questions is best addressed by the experiment? A How do chemical messengers affect a cell's transition between the phases of the cell cycle? B How does the number of chromosomes affect when a cell transitions to the next phase of the cell cycle? C How does the amount of genetic information change throughout the cell cycle? D How does the checkpoint at G2G2 serve to prevent the transmission of mutations?

A

A DNADNA mutation changes the shape of the extracellular domain of transmembrane receptor protein AA produced by the cell. Which of the following predictions is the most likely consequence of the mutation? A Production of activated molecule 1 will stop, but production of activated molecules 2 and 3 will continue. B The molecule that normally binds to protein AA will no longer attach, deactivating the cellular response. C The molecule that normally binds to protein AA will not enter the cell, thus no cellular response will occur. D Since protein AA is embedded in the membrane, the mutation will be silent and not affect the cellular response.

B

A researcher examining a root tip observes a plant cell with condensed sister chromatids, kinetochores with attached microtubules, and individual chromosomes that are aligned at the equatorial plate of the cell. Which of the following best describes what the next process will be in the cell? A Homologous chromosomes (each with two sister chromatids) will move toward opposite poles of the cell. B Paired chromatids will separate, and the new daughter chromosomes will move toward opposite poles of the cell. C The nuclear envelope will break down, and the spindle will begin to form. D The chromatin will decondense, and the daughter cell will enter interphase.

B

Air is less dense at very high elevations, so less oxygen is available than in the denser air at sea level. Based on the model in Figure 1, if a person travels from sea level to a high elevation location, which of the following correctly predicts the response to the decreased blood oxygen level? A More erythropoietin will be secreted from the kidneys, decreasing production of erythrocytes. B More erythropoietin will be secreted from the kidneys, increasing production of erythrocytes. C Less erythropoietin will be secreted from the kidneys, decreasing production of erythrocytes. D Less erythropoietin will be secreted from the kidneys, increasing production of erythrocytes.

B

Argatroban is a competitive inhibitor of thrombin. Which of the following effects on the coagulation cascade is most likely to result from inhibiting thrombin activity with argatroban? A The activation of clotting factors will be blocked. B The rate of fibrin formation will decrease. C Thrombin will be converted to prothrombin. D The rate of blood clot formation will increase.

B

Based on Figure 1, which of the following describes the role of cyclin in the regulation of the cell cycle? A During G1G1 phase, the cyclin level decreases to signal the start of the resting phase of the cell cycle. B During MM phase, the cyclin level peaks, resulting in an increased binding frequency with CDKCDK. C During SS phase, the cyclin level remains the same because DNADNA replication is occurring. D During G2G2 phase, the cyclin level remains low, causing MPFMPF activity to decrease, which leads cells to initiate mitosis.

B

Based on Figure 1, which of the following statements best describes the epinephrine signaling pathway? A It involves the opening and closing of ion channels. B In involves enzymes activating other enzymes. C It involves changes in the expression of target genes. D It involves protons moving down a concentration gradient.

B

Based on the information provided, which of the following best justifies the claim that osteocalcin is a hormone? A The phosphorylation of the insulin receptor causes a response in osteoblast bone cells. B The osteoblasts in the bone secrete osteocalcin, which causes cells in the pancreas to change their activity. C The change in expression of EspEsp changes the insulin receptor activity of the osteoblast. D The activation of the osteocalcin by a bone cell is pHpH dependent.

B

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

B

During mitosis, which of the following normally occurs? A Homologous chromosomes pair. B Replicated chromosomes line up on the equatorial plate. C Tetrads form. D Unreplicated chromosomes become oriented in the center of the cell. E Maternal and paternal chromatids pair.

B

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.

B

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.

B

Trypsinogen is split by the enzyme enterokinase to form an activated molecule of the protease trypsin. Which of the following would confirm that the activation of trypsin is an example of how a positive feedback mechanism can amplify a biological process? A The activated trypsin enzyme can use enterokinase as a substrate. B The trypsin produced by the reaction is capable of splitting and activating additional trypsinogen molecules. C If levels of trypsin were to get too high, the trypsin molecules would inhibit the enzyme enterokinase. D Each mRNA molecule that codes for trypsinogen can be translated repeatedly to form many peptide molecules.

B

Which of the following best describes the data in Figure 1 ? A As the concentration of drug XX increases, there is an increase in melanoma cell survival. B At a concentration above 10 μM10 μM, drug XX reduces melanoma cell survival. C At a concentration below 25 μM25 μM, drug XX increases survival in all melanoma cell lines. D At a concentration of 25 μM25 μM, drug XX has a greater effect on melanoma line 11 than on melanoma line 22.

B

Which of the following best describes the production of DMSPDMSP by coral and coral symbionts? A A negative feedback mechanism that increases the environmental change B A negative feedback mechanism that reverses the environmental change C A positive feedback mechanism that increases the environmental change D A positive feedback mechanism that reverses the environmental change

B

Which of the following is represented by the gradual increase in thickness of the arrows from the top to the bottom of Figure 1 ? A The rate at which nitric oxide triggers signaling gradually increases over time. B The number of signaling molecules that are produced or activated increases with each step in the pathway. C The size of the proteins in the pathway increases as the signaling cascade moves through the cell. D The signaling pathway uses an increase in negative feedback to reduce intracellular Ca2+Ca2+ levels and cell sensitivity to Ca2+Ca2+.

B

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.

B

Which of the following research questions would best guide an investigation of the link between the structure of the signaling molecules and the evolution of quorum sensing? A Do these molecules require the same receptors in each bacteria species to generate a response? B Did these species evolve from a common ancestor that used a similar signaling molecule? C Do these species all perform the same action when the concentration of the signaling molecules is high enough? D Did these species evolve from the same common ancestor that is still living today and uses the same receptors?

B

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.

B

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? A The transduction of the glucocorticoid signal across the plasma membrane will be blocked. B The glucocorticoid receptor will remain associated with the accessory proteins. C The rate of diffusion of glucocorticoid molecules into the cell will increase. D The concentration of glucocorticoid receptors inside the nucleus will increase.

B

A researcher has identified a compound that reverses the effect of drug XX. Based on Figure 3, which of the following best explains how the compound acts in the pathway to reverse the effects of drug XX? A compound arrow molecule B compound line molecule A C compound line molecule B D compound line molecule C

C

Based on Figure 1, which of the following best explains how exercise causes blood glucose levels to rise? A Epinephrine inhibits alpha cells, causing the release of glucagon, and activates beta cells, blocking the release of insulin. B Epinephrine activates alpha cells, blocking the release of glucagon, and inhibits beta cells, causing the release of insulin. C Epinephrine activates alpha cells, causing the release of glucagon, and inhibits beta cells, blocking the release of insulin. D Epinephrine inhibits alpha cells, blocking the release of glucagon, and activates beta cells, causing the release of insulin.

C

Based on Figure 2, which of the following best supports the claim that drug X inhibits oxygen consumption? A In the absence of drug X, melanoma lines 11 and 44 consume similar amounts of oxygen. B In the presence of drug X, melanoma line 22 consumes statistically more oxygen per cell than does melanoma line 33. C Melanoma line 33 consumes statistically less oxygen per cell in the presence of drug X than it does in the presence of the solvent alone. D Melanoma line 22 in the presence of drug X consumes statistically less oxygen than does melanoma line 44 in the absence of drug X.

C

Based on the experimental results, which of the following describes the most likely defect in muscle cells of patients with type 2 diabetes? A Insulin receptor proteins do not reach the cell surface. B Insulin does not activate its receptor. C IRS-1 activation is reduced at high insulin concentrations. D GLUT4 blocks glucose from entering cells.

C

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.

C

Cyclic AMPAMP phosphodiesterase is an enzyme that catalyzes the conversion of cyclic AMPAMP to a different molecule. Which of the following best predicts the effect of inhibiting cyclic AMPAMP phosphodiesterase in a muscle cell stimulated by epinephrine? A The concentration of cyclic AMPAMP will decrease because adenylyl cyclase will no longer be activated. B The G protein will diffuse out of the cell because it will no longer bind to the plasma membrane. C Phosphorylase kinase will remain active because protein kinase A will no longer be deactivated. D Glycolysis will stop because epinephrine signaling will no longer stimulate glycogen breakdown.

C

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

C

One approach to treating patients with pancreatic cancer and other cancers in which the Hedgehog protein is detected is to modify the Hedgehog signaling pathway. Which of the following is the most useful approach? 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

C

Researchers studying cell cycle regulation in budding yeast have observed that a mutation in the CDC15 gene causes cell cycle arrest in telophase when the yeast cells are incubated at an elevated temperature. Which of the following statements best predicts the effect of the cell cycle arrest on proliferating yeast cells? A The yeast cells will transition out of G0G0 but will fail to complete the G1G1 phase. B The yeast cells will initiate mitosis but will fail to complete the G2G2 phase. C The yeast cells will replicate their chromosomes but will fail to complete cytokinesis. D The yeast cells will replicate their organelles but will fail to complete the S phase.

C

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? A The proteins receive electrical signals from nerve cells. B The proteins leave the cell and travel in the bloodstream to other cells. C The proteins interact directly with proteins on the surfaces of other cells. D The proteins bind to molecules secreted by cells located in other parts of the body.

C

Which of the following best describes the scientists' findings concerning the density of symbionts presented in Figure 2 ? A The symbiont density at 32°C32°C on day 55 was less than the density on day 00 of the experiment. B The symbiont density at 27°C27°C on day 00 was less than the density on day 55 of the experiment. C The symbiont density at 32°C32°C was different from the density at 27°C27°C on days 55 and 1010 of the experiment. D The symbiont density at 27°C27°C was higher than the density at 32°C32°C for the entire length of the experiment.

C

Which of the following best explains the most likely method by which this antitumor drug works? A Trabectedin increases the production of cyclin proteins that signal the cancer cells to enter prophase. B Trabectedin interferes with the plasma membrane, causing it to break down and expose the DNADNA to damage. C Trabectedin interferes with the duplication of DNADNA during interphase and thus prevents cancer cells from passing the G2G2 checkpoint. D Trabectedin interferes with the regulations of cyclin proteins, causing their levels to increase and creating errors in DNADNA.

C

Which of the following best represents two different signaling pathways that share a second messenger? A two-one-one-one B one-one-two-one C two-two-one-two D two-two-two-two

C

Which of the following describes a mutation that would lead to an increase in the frequency of nondisjunction? A A mutation affecting checkpoint 11 proteins that forces cells to enter G0G0 B A mutation affecting checkpoint 22 proteins that allows cells to divide with DNADNA damage C A mutation affecting checkpoint 33 proteins that prevents attachment of spindle fibers D A mutation affecting checkpoint 22 proteins that prevents duplication of the chromosomes

C

Which of the following describes the most likely consequence of a negative feedback pathway involving the lac operon? A The breakdown products of lactose block cell division. B Diffusion of lactose across the plasma membrane would stop in the presence of lactose. C Expression of the lac operon diminishes as lactose is depleted. D Binding of DNA by the repressor would increase in the presence of lactose.

C

Which of the following occurs in both meiosis and mitosis? A Separation of homologous chromosomes B Reduction of chromosome number C Separation of sister chromatids D Crossing-over between homologous chromosomes E Production of four daughter cells

C

Which of the following patterns is shown by the data? A Mutant 1 cells are more similar to mutant 3 cells than to wild-type cells. B In wild-type cells, the percent of cells in anaphase is twice the amount of those in telophase C In mutant 3 cells, more time is spent in prophase/prometaphase than in the later stages of mitosis. D The percent of mutant 2 cells in anaphase is higher than that of mutant 1 cells.

C

Which of the following presents a correct interpretation of the changes in chromosome number depicted in Figure 1 ? A DNADNA replication occurs between metaphase and anaphase, doubling the number of chromosomes. Between telophase and cytokinesis, the cell divides in two, with each cell receiving half of the replicated chromosomes. B New chromosomes formed during prophase are doubled during anaphase and are recombined before cytokinesis. C 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. D At anaphase a cell contains two identical copies of each chromosome, but following telophase, one of the copies is broken down into nucleotides.

C

Which of the following statements best describes the role of adenylyl cyclase in the epinephrine signaling pathway? A It converts a polymer to its monomer subunits. B It moves substances across the plasma membrane. C It accelerates the production of a second messenger. D It transfers phosphate groups from ATPATP to protein substrates.

C

Which of the following statements best describes the role of cyclic AMPAMP in the signal transduction pathway? A It acts as a signaling molecule that passes the signal from the cell to other cells. B It acts as a receptor that carries the signal from outside the cell to inside the cell. C It acts as a second messenger that helps relay and amplify the signal within the cell. D It acts as a channel protein that transmits the signal across the cell's nuclear membrane.

C

Which of the following statements best explains Delta's role in regulating cell communication through the Notch signaling pathway? A Delta transmits a chemical signal to all the cells of a developing embryo. B Delta allows the cells of a developing embryo to communicate without making direct contact. C Delta restricts cell communication to short distances within a developing embryo. D Delta determines which cells in a developing embryo express the gene that encodes the Notch protein.

C

A researcher claims that the epinephrine signaling pathway controls a catabolic process in muscle cells. Which of the following statements best helps justify the researcher's claim? A Epinephrine is a signaling molecule that binds to a transmembrane protein. B The G protein in the epinephrine signaling pathway consists of three different subunits. C Phosphorylase kinase catalyzes the hydrolysis of ATPATP. D Glycogen phosphorylase catalyzes the conversion of glycogen to glucose-1-phosphate.

D

Based on Figure 1, what percent of the time required to complete a full cycle do the cells typically spend in interphase? A 5% B 35% C 50% D 95%

D

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.

D

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? A A decrease in iron levels activates the IRP. The IRP in turn activates iron transport proteins in the cell membrane, thereby returning free iron levels to normal. B A decrease in iron levels activates synthesis of ferritin protein. Ferritin protein in turn releases bound iron, thereby returning free iron levels to normal. C An increase in iron levels activates the IRP. The IRP in turn binds iron, thereby decreasing both free iron levels and ferritin synthesis. D 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.

D

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? A Activated platelets release chemicals that inhibit blood clot formation. B Activated platelets release signaling molecules that inhibit cell division in damaged tissue. C Activated platelets constrict the blood vessels, stopping blood flow. D Activated platelets release chemicals that activate more platelets.

D

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? A Estrogen from the ovaries inhibits the release of GnRHGnRH from the hypothalamus. B Progesterone from the ovaries stimulates the thickening of the uterine lining. C Progesterone from the ovaries inhibits the release of LHLH and FSHFSH from the anterior pituitary. D Estrogen from the ovaries stimulates the hypothalamus and anterior pituitary to secrete more GnRHGnRH, LHLH, and FSHFSH.

D

In flowering plants, plasmodesmata are narrow channels through cell walls that connect the cytoplasms of adjacent cells. An explanation of how plant cells communicate across cell walls will most likely refer to the diffusion through plasmodesmata of which of the following? A Membrane-bound organelles B Condensed, duplicated chromosomes C Branched polysaccharides D Small, water-soluble molecules

D

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

D

What is the expected percent change in the DNADNA content of a typical eukaryotic cell as it progresses through the cell cycle from the start of the G1G1 phase to the end of the G2G2 phase? A −100%−100% B −50%−50% C +50%+50% D +100%

D

Which of the following best describes how the amount of DNADNA in the cell changes during MM phase? A The amount of DNADNA doubles as the DNADNA is replicated. B The amount of DNADNA slightly increases as a result of new organelle synthesis. C The amount of DNADNA does not change while the cell grows. D The amount of DNADNA is halved as the cell divides into two daughter cells.

D

Which of the following best supports the claim that ethylene initiates the signal transduction pathway that leads to ripening of fruit? A Ethylene is a simple gaseous molecule, which makes it easily detected by receptors. B Fruit will ripen in closed containers without exposure to air. C Ethylene synthesis is under both positive and negative feedback regulation. D Loss-of-function mutations in ethylene receptors result in changes to the ripening process.

D

Which of the following conditions will most likely cause a normal body cell to become a cancer cell? A The environment already contains cancer cells. B The environment has an abundance of nutrients. C The environment lacks signals that would otherwise tell the cell to stop dividing. D The environment contains mutagens that induce mutations that affect cell-cycle regulator proteins.

D

Which of the following was a positive control in the experiment? A Minutes after glucose injection B Blood insulin C Mutant strain D Normal strain

D