Apentix/AP Biology/Unit 2: Cell Structure and Function/Question
AP Biologymediummcq1 pt

Measurements put the lysosomal interior near pH 4.7 while the neighboring cytosol sits close to pH 7.2. What sustains this steep proton imbalance across the lysosomal membrane?

A.A membrane-spanning pump hydrolyzes ATP to force protons into the lysosome against their gradient
B.Protons trickle inward passively until both compartments reach the same acidity
C.Cleaving polymers liberates enough protons to acidify the lumen unaided
D.The membrane ejects hydroxide ions faster than protons escape

Explanation

Core Concept

V-type ATPases embedded in the lysosomal membrane use ATP energy to push H+ inward, building and holding the acidic lumen despite constant leakage. The arrangement follows the logic of any electrochemical gradient: continuous energy input, not equilibrium, maintains the imbalance. Acidic conditions then let the resident hydrolases work at full catalytic rate.

Correct Answer

AA membrane-spanning pump hydrolyzes ATP to force protons into the lysosome against their gradient

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