A substance that can take up excess hydrogen or excess hydroxide is a/an

Correct Answer: B

Rationale: A buffer takes up excess H or OH⁻ e.g., HCO₃⁻ neutralizes (pH stability). Acid donates H not absorbs. Base takes H not OH⁻. Salt is neutral non-buffering. Buffer's dual capacity distinguishes it, key to homeostasis, unlike one-way or neutral substances.

Correct Answer: A

Rationale: Sodium balance hinges on GFR (filtration rate) and Na reabsorption e.g., PCT (65%), aldosterone (distal). GFR/renin ties BP not direct Na . Na /K links aldosterone partial view. None denies control false. GFR/reabsorption synergy distinguishes it, critical for Na homeostasis, unlike partial or null options.

Correct Answer: C

Rationale: Countercurrent exchange concentrates urine Loop of Henle/vasa recta gradient (e.g., ~1200 mOsm medulla). Bicarbonate buffers pH not concentration. Renin-angiotensin regulates BP not urine osmolality. Densification isn't a term false. Countercurrent's gradient distinguishes it, key to urine concentration, unlike buffering or BP systems.

Correct Answer: C

Rationale: Collecting ducts set urine osmolality ADH aquaporins adjust (e.g., 50-1200 mOsm). Water secretion is false reabsorbed. Most reabsorption is PCT (~65%) not collecting. ADH increases permeability opposite. Osmolality control distinguishes it, critical for concentration, unlike secretion or misattributed roles.

Correct Answer: A

Rationale: ADH is synthesized in the hypothalamus e.g., supraoptic nuclei, released by pituitary for water retention. JG cells secrete renin not ADH. Tube is ureter unrelated. Micturition is urination not hormone. Hypothalamic synthesis distinguishes it, critical for osmoregulation, unlike renal or action terms.