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

An Elodea leaf is mounted in concentrated saltwater, and within minutes its green chloroplasts draw away from the cell wall, leaving a clear gap between wall and membrane. What happened?

A.The hypertonic bath pulled water out of the cell until the membrane shrank away from the rigid wall
B.Salt rushed in and burst the central vacuole
C.The wall absorbed water and stretched away from the membrane
D.Chloroplasts migrated inward to avoid the microscope light

Explanation

Core Concept

Saltwater holds a lower water potential than the cell sap, so osmosis carries water out through the membrane. The protoplast loses volume and pulls inward while the stiff wall keeps its shape, producing the visible gap called plasmolysis. Returning the leaf to hypotonic water reverses the process as water reenters and turgor pressure rebuilds.

Correct Answer

AThe hypertonic bath pulled water out of the cell until the membrane shrank away from the rigid wall

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