Proton pumps in acid-secreting and ion-regulating tissues

Steps:

• Recall proton pumps (H+-ATPases) function in active transport of H+ ions across membranes.
• Identify tissues: R labels gastric parietal cells (stomach acid secretion), S labels renal collecting duct cells (urine acidification).
• Eliminate tissues without proton pumps: Q (e.g., skeletal muscle) and T (e.g., connective tissue) lack them.
• Match to choices: Only C pairs tissues with proton pumps.

Why C is correct:

• R and S contain vacuolar H+-ATPases for HCl production in stomach and H+ excretion in kidneys, per cellular physiology definitions.

Why the others are wrong:

• A: Q lacks proton pumps, as muscle uses Na+/K+-ATPase instead.
• B: Q and T both lack proton pumps; T involves no ion secretion.
• D: T lacks proton pumps, focusing on structural support without active H+ transport.

Final answer: C