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

Leaf cells remain firm when their surroundings are hypotonic to the cytoplasm. What sustains that firmness?

A.Active transport pumps water into the vacuole faster than it leaks back out.
B.Osmotic water entry swells the central vacuole against the rigid wall, generating turgor pressure.
C.The wall contracts inward around the shrinking protoplast, squeezing fluid upward.
D.Solutes are exported until the cytoplasm matches the exterior, and firmness persists from leftover suction.

Explanation

Core Concept

Water enters by osmosis and presses the protoplast outward against the cell wall. The wall pushes back with equal mechanical force, producing turgor pressure that stiffens the tissue without bursting the cell. Walled cells thereby tolerate hypotonic environments that would lyse an animal cell.

Correct Answer

BOsmotic water entry swells the central vacuole against the rigid wall, generating turgor pressure.

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