AP Classroom Cell Signals Practice

When the concentration of GAl is highest, the average height of the control seedlings is approximately A 10 cm B 30 cm C 60 cm D 85 cm E 95 cm

A 10 cm

The diagram above shows a developing worm embryo at the four-cell stage. Experiments have shown that when cell 3 divides, the anterior daughter cell gives rise to muscle and gonads and the posterior daughter cell gives rise to the intestine. However, if the cells of the embryo are separated from one another early during the four-cell stage, no intestine will form. Other experiments have shown that if cell 3 and cell 4 are recombined after the initial separation, the posterior daughter cell of cell 3 will once again give rise to normal intestine. Which of the following is the most plausible explanation for these findings? A A cell surface protein on cell 4 signals cell 3 to induce formation of the worm's intestine. B The plasma membrane of cell 4 interacts with the plasma membrane of the posterior portion of cell 3, causing invaginations that become microvilli. C Cell 3 passes an electrical signal to cell 4, which induces differentiation in cell 4. D Cell 4 transfers genetic material to cell 3, which directs the development of intestinal cells.

A A cell surface protein on cell 4 signals cell 3 to induce formation of the worm's intestine.

The diagram above shows a developing worm embryo at the four-cell stage. Experiments have shown that when cell 3 divides, the anterior daughter cell gives rise to muscle and gonads and the posterior daughter cell gives rise to the intestine. However, if the cells of the embryo are separated from one another early during the four-cell stage, no intestine will form. Other experiments have shown that if cell 3 and cell 4 are recombined after the initial separation, the posterior daughter cell of cell 3 will once again give rise to normal intestine. Which of the following is the most plausible explanation for these findings? A A cell surface protein on cell 4 signals cell 3 to induce formation of the worm's intestine. B The plasma membrane of cell 4 interacts with the plasma membrane of the posterior portion of cell 3, causing invaginations that become microvilli. C Cell 3 passes an electrical signal to cell 4, which induces differentiation in cell 4. D Cell 4 transfers genetic material to cell 3, which directs the development of intestinal cells.

A A cell surface protein on cell 4 signals cell 3 to induce formation of the worm's intestine.

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.

A As tissue osmolarity rises, more ADH is released, causing less water to be excreted as urine.

Based on your understanding of the ways in which signal transmission mediates cell function, which of the following predictions is most consistent with the information given above? A In an environment with low fixed nitrogen, treating the Anabaena cells with a calcium-binding compound should prevent heterocyst differentiation. B A strain that overexpresses the patS gene should develop many more heterocysts in a low fixed nitrogen environment. C In an environment with abundant fixed nitrogen, free calcium levels should be high in all cells so that no heterocysts develop. D In environments with abundant fixed nitrogen, loss of the hetR gene should induce heterocyst development.

A In an environment with low fixed nitrogen, treating the Anabaena cells with a calcium-binding compound should prevent heterocyst differentiation.

Which of the following is a correct conclusion that can be drawn from the data in Figures 1, 2, and 3? A Most of the increase in the concentration of all gibberellins 40 to 45 days after planting is due to an increase in the concentration of GAl. B The concentration of all gibberellins is three times as great at 75 days as it is at 30 days after planting. C An increase in GAl levels occurs a day or two before the seedlings start to grow rapidly. D An increase in the concentration of GAl inhibits the synthesis of other gibberellins. E The concentration of GAl is a thousand times as great at 45 days as it is at 30 days after planting.

A Most of the increase in the concentration of all gibberellins 40 to 45 days after planting is due to an increase in the concentration of GAl.

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 The rate of the pyruvate dehydrogenase-catalyzed reaction is slower in the presence of a higher concentration of acetyl-CoACoA.

Figure 2: Variation in symbiont density and photosynthetic yield in adult corals grown in normal and thermally-stressed conditions. Error bars represent ±2SEx¯±2SE�¯. 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 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? 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.

B ADH promotes an increase in the movement of water into the bloodstream.

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 μM, drug XX reduces melanoma cell survival. C At a concentration below 25 μM, drug XX increases survival in all melanoma cell lines. D At a concentration of 25 μM, drug XX has a greater effect on melanoma line 11 than on melanoma line 22.

B At a concentration above 10 μM, drug XX reduces melanoma cell survival.

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.

B Calcitonin levels will rise, thus promoting the deposit of calcium into bones.

Previous experiments indicate that CDK5CDK5 is active only when attached to a protein called p35p35. Which of the following best predicts how p35p35 might play a role in regulating neuron function? A Elevated intracellular levels of p35p35 result in increased synaptic activity. B Degradation of p35p35 results in increased synaptic activity. C Reabsorption of p35p35 from the synaptic cleft results in increased synaptic activity. D Attachment of p35p35 to synaptic vesicles results in increased synaptic activity.

B Degradation of p35p35 results in increased synaptic activity.

Figure 1. The chemical structure of several molecules used for quorum sensing in three species of bacteria 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 Did these species evolve from a common ancestor that used a similar signaling molecule?

Based on the model, which of the following best explains how regulation of neurotransmitter release might increase the range of responses to a stimulus in the nervous system? A In the absence of any stimulus, neurons can still release neurotransmitters. B Different neurons in the same neural network can release different amounts of neurotransmitter. C In the depolarization phase of an action potential, postsynaptic neurons can adjust the amount of neurotransmitter bound to receptors on their surface. D In the recovery phase following a stimulus, enzymes can be mobilized to degrade molecules present in the synaptic vesicles.

B Different neurons in the same neural network can release different amounts of neurotransmitter.

Which of the following is a correct conclusion that can be drawn based only on the data in Figure 4? A Seedling growth rates decrease between 50 and 80 days after planting at all concentrations of the inhibitor. B The greater the inhibition of GAl synthesis, the lower the plant height after 80 days. C The spraying of GAl on seedlings results in an increase in seedling growth rates. D The inhibitor kills the seedlings when it is applied in very high concentrations. E The growth of the seedlings is directly proportional to the concentrations of inhibitor.

B The greater the inhibition of GAl synthesis, the lower the plant height after 80 days.

The concentration of all gibberellins 65 days after planting is approximately A 5 ng/gram B 10 ng/gram C 20 ng/gram D 120 ng/gram E 150 ng/gram

C 20 ng/gram

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? 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 Epinephrine activates alpha cells, causing the release of glucagon, and inhibits beta cells, blocking the release of insulin.

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 withCAMsCAMs, causing the cell cycle to stop permanently. B The ras protein will remain bound to DNADNA, 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.

C Growth-factor signaling can trigger mitosis in cells that are in direct contact with other cells.

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.

C Similar cell signaling pathways in diverse eukaryotes are evidence of conserved evolutionary processes.

Figure 2: Variation in symbiont density and photosynthetic yield in adult corals grown in normal and thermally-stressed conditions. Error bars represent ±2SEx¯±2SE�¯. 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 The symbiont density at 32°C32°C was different from the density at 27°C27°C on days 55 and 1010 of the experiment.

A researcher has identified a compound that reverses the effect of drug X. Based on Figure 3, which of the following best explains how the compound acts in the pathway to reverse the effects of drug X?

Compound over Complex B

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? Responses 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.

D A decrease in thyroxine levels means a loss of inhibition to the hypothalamus and anterior pituitary, leading to increased TSH secretion.

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 Activated platelets release chemicals that activate more platelets.

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

D Increased mobilization of fatty acids from fat cells

Which of the following observations best supports the hypothesis that CDK5CDK5negatively regulates neurotransmitter release? A Introduction of CDK5CDK5 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 CDK5CDK5 by neurons results in the movement of synaptic vesicles to the plasma membrane in the absence of any stimulus. C Suppression of CDK5CDK5 expression in neurons inhibits the movement of synaptic vesicles to the plasma membrane in response to a specific stimulus. D Inhibition of CDK5CDK5 activity in neurons increases the movement of synaptic vesicles to the plasma membrane in response to a specific stimulus.

D Inhibition of CDK5CDK5 activity in neurons increases the movement of synaptic vesicles to the plasma membrane in response to a specific stimulus.