AP Bio Unit 4 Review

Following surgical removal of the thyroid gland, the level of thyroid-stimulating hormone (TSH) in the blood will increase. Which of the following best explains this increase?

• Residual blood thyroxine, from prior to thyroid gland removal, will bind to cells in the anterior pituitary, signaling more TSH secretion.

• 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.

• Thyroxine that was stored in the anterior pituitary prior to thyroid gland removal will signal more TSH secretion.

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

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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 sodium into the bloodstream.

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

• ADH promotes an increase in the excretion of water from the body.

• ADH promotes an increase in the secretion of additional ADH from the pituitary gland.

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Which of the following best describes how the amount of DNA in the cell changes during M phase?

• The amount of DNA doubles as the DNA is replicated

• The amount of DNA slightly increases as a result of new organelle synthesis.

• The amount of DNA does not change while the cell grows.

• The amount of DNA is halved as the cell divides into two daughter cells

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As shown in the diagram above, when there is low fixed nitrogen in the environment, an increase in the concentration of free calcium ions and 2-oxyglutarate stimulates the expression of genes that produce two transcription factors (NtcA and HetR) that promote the expression of genes responsible for heterocyst development. HetR also causes production of a signal, PatS, that prevents adjacent cells from developing as heterocysts.

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?

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

• A strain that overexpresses the patS gene should develop many more heterocysts in a low fixed nitrogen environment.

• In an environment with abundant fixed nitrogen, free calcium levels should be high in all cells so that no heterocysts develop.

• In environments with abundant fixed nitrogen, loss of the hetR gene should induce heterocyst development.

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?

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

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

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

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

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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 decline, thus stimulating the release of PTH.

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

• PTH levels will decline, thus stimulating the loss of calcium from bones.

• PTH levels will increase, thus preventing the release of calcitonin.

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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 receptor mutation results in activation of a cell-division pathway in the absence of the appropriate ligand.

• A mutation results in the loss of the ability to produce a tumor-suppressor protein.

• A defect in a cell-cycle checkpoint prevents a cell from entering the S phase

• At the anaphase checkpoint, separation of chromatids occurs without all centromeres being attached to kinetochore microtubules from both poles.

Most cells that have become transformed into cancer cells have which of the following characteristics when compared to normal, healthy cells?

• Shorter cell cycle

• More carefully regulated rates of cell division

• Lower rates of mitosis

• Higher rates of protein translation

• Identical DNA

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

• Introduction of CDK5 protein into neurons results in the movement of synaptic vesicles to the plasma membrane in the absence of any stimulus.

• Uptake of a gene encoding CDK5 by neurons results in the movement of synaptic vesicles to the plasma membrane in the absence of any stimulus.

• Suppression of CDK5 expression in neurons inhibits the movement of synaptic vesicles to the plasma membrane in response to a specific stimulus.

• Inhibition of CDK5 activity in neurons increases the movement of synaptic vesicles to the plasma membrane in response to a specific stimulus.

Researchers investigating the regulation of neurotransmitter release from presynaptic neurons proposed a model (Figure 1) in which CDK5, a protein expressed in axon terminals, inhibits the movement of synaptic vesicles to the presynaptic membrane. To test their model, the researchers used a modified version of green fluorescent protein (GFP). In slightly alkaline conditions, GFP exhibits a bright green fluorescence. In acidic conditions, GFP exhibits no fluorescence. Using standard techniques, the gene encoding GFP is easily introduced into living cells. By engineering the expression of GFP in laboratory-cultured nerve cells, the researchers found that a bright green fluorescence was exhibited only when a presynaptic neuron was given a certain stimulus. Previous experiments indicate that CDK5 is active only when attached to a protein called p35. Which of the following best predicts how p35 might play a role in regulating neuron function?

• Elevated intracellular levels of p35 result in increased synaptic activity

• Degradation of p35 results in increased synaptic activity

• Reabsorption of p35 from the synaptic cleft results in increased synaptic activity

• Attachment of p35 to synaptic vesicles results in increased synaptic activity