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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NGSS.HS-LS1-3

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

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.

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.

The graph shows changes in glucagon and insulin secretions at different concentrations of blood glucose. Which of the following feedback mechanisms is best supported by the data?

• A falling glucagon level causes a rise in the insulin level, which maintains equal amounts of both hormones in the blood.

• A high glucagon level causes a rise in the insulin level, which maintains high levels of both hormones in the blood.

• A low glucose level causes the release of glucagon, which stimulates the release of more glucose from tissues, which in turn lowers the amount of glucagon being released.

• A low glucose level causes the release of insulin, which stimulates the release of more glucose from tissues, which in turn increases the amount of insulin being released.

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The vertebrate forelimb initially develops in the embryo as a solid mass of tissue. As development progresses, the solid mass near the end of the forelimb is remodeled into individual digits. Which of the following best explains the role of apoptosis in remodeling of the forelimb?

• Apoptosis replaces old cells with new ones that are less likely to contain mutations.

• Apoptosis involves the regulated activation of proteins in specific cells of the developing forelimb that leads to the death of those cells.

• Apoptosis involves the destruction of extra cells in the developing forelimb, which provides nutrients for phagocytic cells.

• Apoptosis in the developing forelimb triggers the differentiation of cells whose fate was not already determined.

When a stimulus is applied to a receptor in the skin, an action potential is propagated along a neuron to the brain, where another signal is sent back to the muscle for a response.

Which of the following best describes what occurs when the action potential reaches a chemical synapse at the end of an axon?

• The action potential jumps from one axon to the next connecting axon.

• The action potential travels through the synapse to the next connecting dendrite.

• The action potential jumps the synapse to the next connecting dendrite.

• The action potential causes a release of neurotransmitters that travel across the synapse.

Which of the following would be an example of paracrine signaling in animals?

• neurotransmitter acetylcholine
• hormone epinephrine
• neurotransmitter norepinephrine
• growth factor

A signal molecule that binds to a plasma-membrane protein is a

• ligand
• second messenger
• protein kinase
• receptor protein