AP Biology Cell Communication and Cell Cycle Review

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?

• 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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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 change in the cytoskeletal attachment of transmembrane proteins

• The presence of a large amount of the precursor form of the ligand

• An increase in the ratio of the number of unsaturated to the number of saturated fatty acid tails of the membrane lipids

• 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

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?

• Homologous chromosomes (each with two sister chromatids) will move toward opposite poles of the cell.

• Paired chromatids will separate, and the new daughter chromosomes will move toward opposite poles of the cell.

• The nuclear envelope will break down, and the spindle will begin to form.

• The chromatin will decondense, and the daughter cell will enter interphase.

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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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Cell communication is critical for the function of both unicellular and multicellular eukaryotes. Which of the following is likely true of cell signaling?

• Cell signaling uses the highest molecular weight molecules found in living cells.

• Cell signaling has largely been replaced by other cell functions in higher mammals.

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

• Cell signaling functions mainly during early developmental stages.

During mitosis, which of the following normally occurs?

• Homologous chromosomes pair.

• Replicated chromosomes line up on the equatorial plate.

• Tetrads form.

• Unreplicated chromosomes become oriented in the center of the cell.

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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?

• Epinephrine binds to a cell-surface receptor; the activated receptor stimulates production of the second messenger, cAMP

  .

• Epinephrine binds to a cell-surface receptor; the activated receptor catalyzes the conversion of glycogen to glucose.

• Epinephrine diffuses through the plasma membrane; the hormone dimerizes in the cytosol.

• Epinephrine is taken into the cell by endocytosis; glycogen is converted to glucose in the endocytotic vesicle.

Many human cells can be stimulated to divide by hormonelike growth factors that bind to receptor proteins (R) on the plasma membrane and trigger an internal signal-transduction cascade. In many cases, however, the process of contact inhibition prevents mitosis when cells are in direct contact with one another. Contact inhibition occurs when proteins called cell adhesion molecules (CAMs

) interact, causing them to change shape so that the growth-factor signaling proteins that normally associate with CAMs are replaced by another protein, called M. Both pathways are depicted in the figures.

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?

• Protein 3 will be prevented from interacting with CAMs, causing the cell cycle to stop permanently.

• The ras protein will remain bound to DNA, blocking expression of genes required for mitosis.

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

• The receptor proteins of body cells will no longer bind to growth-factor proteins.

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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

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The endocrine system incorporates feedback mechanisms that maintain homeostasis. Which of the following demonstrates negative feedback by the endocrine system?

• During labor, the fetus exerts pressure on the uterine wall, inducing the production of oxytocin, which stimulates uterine wall contraction. The contractions cause the fetus to further push on the wall, increasing the production of oxytocin

• 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.

• At high elevation, atmospheric oxygen is more scarce. In response to signals that oxygen is low, the brain decreases an individual’s rate of respiration to compensate for the difference.

• A transcription factor binds to the regulatory region of a gene, blocking the binding of another transcription factor required for expression.

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