What separates the ECF and ICF?

Correct Answer: A

Rationale: The correct answer is A: plasma membrane. This is because the plasma membrane is a selectively permeable barrier that separates the extracellular fluid (ECF) outside the cell from the intracellular fluid (ICF) inside the cell. It regulates the movement of substances in and out of the cell, maintaining the internal environment of the cell. Choice B (blood-brain barrier) is incorrect as it specifically refers to a barrier within the brain that regulates the passage of substances between the blood and the brain tissue, not between ECF and ICF. Choice C (blood vessel walls) is incorrect as blood vessel walls primarily regulate the exchange of substances between the blood and tissues, not between ECF and ICF. Choice D (transcellular membrane) is incorrect as it is not a commonly recognized term in cell biology. The term transcellular transport refers to the movement of substances across a cell, which is facilitated by various cellular structures including the plasma membrane.

Correct Answer: C

Rationale: The correct answer is C because the renin-angiotensin-aldosterone system promotes an increase in arterial blood pressure by promoting Na+ reabsorption in the distal and collecting tubules. This leads to an increase in blood volume and subsequently an increase in blood pressure. The other choices are incorrect because: A: Water reabsorption through vasopressin release does not directly contribute to an increase in arterial blood pressure. B: The baroreceptor reflex helps regulate blood pressure by sensing changes and triggering appropriate responses, but it does not directly promote an increase in arterial blood pressure. D: Vasodilation of the afferent arteriole and increasing glomerular filtration rate actually lead to a decrease in blood pressure by reducing resistance in the kidneys.

Correct Answer: D

Rationale: The correct answer is D because osmolarity refers to the concentration of solutes in a solution. A hypertonic solution has a higher concentration of solutes compared to an isotonic solution, leading to water moving out of cells through osmosis. This definition directly relates to osmolarity. A, B, and C are incorrect as they do not directly relate to osmolarity. Choice A talks about vasopressin secretion in response to water deficit, B discusses urinary output in dehydration, and C is incomplete. These choices do not address the concept of osmolarity, which is about solute concentration in a solution.

Correct Answer: B

Rationale: Correct Answer: B (Ca2+) Rationale: In states of acidosis, the body retains Ca2+ in body fluids to help buffer the excess H+ ions and maintain pH balance. Ca2+ acts as a buffer by binding to excess H+ ions, reducing acidity. Kidneys increase Ca2+ retention to counteract the increased H+ secretion. This relationship helps stabilize the body's pH. Summary: A: Na+ is not directly involved in buffering excess H+ ions during acidosis. C: K+ is not specifically retained in response to increased H+ secretion. D: Cl- is not directly related to buffering and pH balance in acidosis.

Correct Answer: B

Rationale: The correct answer is B because each bicarbonate ion can carry two H+ ions, which helps maintain the pH balance in the extracellular fluid (ECF). When there is an excess of H+ ions, bicarbonate ions bind with them to form carbonic acid, which then dissociates into water and carbon dioxide. This helps prevent drastic changes in pH by removing excess H+ ions. Choice A is incorrect because bicarbonate and carbonic acid levels are tightly regulated in the body. Choice C is incorrect because carbonic acid is a weak acid and does not dissociate easily. Choice D is incorrect because the abundance of bicarbonate and carbonic acid in the plasma alone does not make the buffering system effective; it is the ability of bicarbonate ions to carry H+ ions that makes it effective.