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

A selectively permeable bag filled with 0.4 M sucrose sits in a large beaker of 0.2 M sucrose. Water crosses the bag freely while sucrose cannot cross at all. Predict the net movement of water and explain why.

A.Net flow is inward into the 0.4 M bag, because dissolved sucrose leaves less free water there.
B.Water exits the bag because sugar molecules drag bound water along as they attempt to leave.
C.No net movement occurs because equal volumes of liquid sit on the two sides.
D.Sucrose leaks inward until both sides reach equal concentration, and water then follows passively.

Explanation

Core Concept

Dissolved sucrose ties up water in hydration shells, so the bag holds less free water per unit volume than the surrounding bath. Water therefore diffuses down its own potential gradient toward the region of higher solute concentration. Net movement continues until free water equilibrates on the two sides.

Correct Answer

ANet flow is inward into the 0.4 M bag, because dissolved sucrose leaves less free water there.

More Unit 2: Cell Structure and Function practice questions

Try a random question →

Practice more AP Biology questions with full explanations

Practice Unit 2: Cell Structure and Function Questions →