Most enzymes function optimally at pH?

Correct Answer: B

Rationale: Most human enzymes function optimally at a physiological pH of 7.4, close to blood pH (7.35-7.45), where their active sites maintain proper conformation for catalysis. A pH of 7.8 (A) is slightly alkaline, 6.8 (C) is too acidic for most, and 2 (D) suits gastric enzymes like pepsin, not the majority, making B correct.

Correct Answer: B

Rationale: The kidneys' primary function is blood filtration (B), removing waste (e.g., urea), regulating electrolytes, and maintaining fluid/acid-base balance via glomeruli, producing filtrate for urine. Storage (A) is the bladder's role, contractions (C) aid micturition, and urethra expansion (D) is minor, making B the core function.

Correct Answer: D

Rationale: Inulin measures GFR (A) as it's filtered without tubular handling, its concentration rises in the proximal tubule (B) due to water reabsorption, and PAH measures RPF (C) as it's filtered and secreted, clearing most from plasma. All are true: inulin's properties suit GFR, its concentration reflects reabsorption, and PAH's clearance reflects RPF, making E (all are correct), reassigned as D, correct.

Correct Answer: D

Rationale: Angiotensin II (AII) increases sodium reabsorption (D) in the proximal tubule and via aldosterone, raising blood volume. It indirectly aids water (A), doesn't decrease sodium (B), and isn't self-forming (C), making D the key effect.

Correct Answer: C

Rationale: The collecting duct (C) becomes water-permeable with ADH via aquaporin-2, concentrating urine. The proximal tubule (A) and descending limb (B) are always permeable, and ascending limb (D) is not, making C the ADH-dependent match.