Apentix/AP Biology/Unit 2: Cell Structure and Function/Question
AP Biologyeasymcq1 pt

A plant cell placed in pure water swells and becomes firm but does not burst. Which explanation accounts for this?

A.Aquaporins reverse direction and pump water out of the vacuole
B.The rigid cell wall confines swelling, and turgor pressure pushes the membrane against it
C.The plasma membrane thickens under stretch to hold the cell together
D.Solutes are exported until internal osmolarity matches pure water at once

Explanation

Core Concept

Pure water is strongly hypotonic to the cell sap, so water enters by osmosis and the central vacuole expands. Unlike an animal cell, the plant cell is wrapped in a stiff wall of cellulose microfibrils that resists further expansion. Incoming water therefore raises hydrostatic pressure against the wall until wall stress balances osmotic inflow, producing firm turgidity instead of lysis.

Correct Answer

BThe rigid cell wall confines swelling, and turgor pressure pushes the membrane against it

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