Variation in percentage of body water among individuals is due primarily to differences in which one of these factors?

Correct Answer: A

Rationale: The correct answer is A: amount of adipose tissue. Adipose tissue contains less water compared to muscle tissue, so individuals with higher adipose tissue percentages will have lower body water percentages. This influences overall body water content among individuals. Choices B, C, and D are incorrect because while total muscle mass and vasopressin secretion do play a role in body water regulation, they are not the primary factors influencing variation in body water percentage among individuals. Drinking habits also affect hydration levels but are not the primary determinant of body water percentage variability.

Correct Answer: C

Rationale: The correct answer is C, blood vessel walls. Blood vessel walls separate the two types of extracellular fluid - interstitial fluid and blood plasma. This separation is crucial for maintaining homeostasis by regulating the exchange of nutrients, gases, and waste products between the bloodstream and surrounding tissues. The plasma membrane (choice A) is the boundary between the intracellular and extracellular environments of individual cells, not between the two types of extracellular fluid. The blood-brain barrier (choice B) is a specialized structure that separates the blood from the brain's extracellular fluid to protect the brain from harmful substances, not the two types of extracellular fluid. Transcellular membranes (choice D) refer to specific membranes within cells, not the separation between extracellular fluid types.

Correct Answer: C

Rationale: The correct answer is C: membrane potential. Membrane potential refers to the difference in electrical charge between the inside and outside of a cell due to the unequal distribution of positively and negatively charged ions across the plasma membrane. This potential difference is crucial for various cellular processes such as nerve conduction and muscle contraction. A: Disequilibrium constant is a term used in chemical reactions to describe the ratio of product concentrations to reactant concentrations at equilibrium, not related to the distribution of charged solutes in a cell. B: Charge separation is a generic term and does not specifically refer to the unequal distribution of charged solutes across the plasma membrane. D: Chemical disequilibrium refers to a state where a system is not at equilibrium in terms of chemical reactions, not directly related to the distribution of charged solutes across the membrane.

Correct Answer: C

Rationale: The correct answer is C because baroreceptor reflexes respond to changes in blood pressure by causing vasoconstriction of afferent arterioles, which decreases glomerular filtration rate (GFR) and enhances sodium reabsorption to maintain blood pressure. This mechanism helps regulate sodium balance. A: Release of renin is regulated by the renin-angiotensin-aldosterone system, not baroreceptor reflexes. B: Vasopressin release is primarily regulated by osmoreceptors in the hypothalamus, not baroreceptor reflexes. D: Vasodilation of afferent arterioles would increase GFR and potentially decrease sodium reabsorption, counteracting sodium balance regulation.

Correct Answer: C

Rationale: When a cell is placed in an isotonic solution, the concentration of solutes inside and outside the cell is equal. This balance results in no net movement of water across the cell membrane, leading to the cell maintaining its normal shape and size. Choice A is incorrect because in a hypertonic solution, a cell will shrink due to water leaving the cell. Choice B is incorrect as in a hypotonic solution, a cell will swell due to water entering the cell. Choice D is incorrect as it does not provide any relevant information. Therefore, choice C is the correct answer as the cell will stay the same size in an isotonic solution.