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A red blood cell is placed into a solution. The intracellular fluid and the surrounding solution have equal osmolality but different solute compositions.
What is the net movement of water across the cell membrane? Select ONE answer only.
10.17%
Active transport of water across the membrane
4.46%
Continuous unidirectional movement of water
9.14%
Net movement of water into the cell
9.83%
Net movement of water out of the cell
66.29%
No net movement of water

Explanation:

Water movement is determined by osmolality, not the specific type of solute.

 

If the intracellular fluid and the surrounding solution have equal osmolality, there is no osmotic gradient, so there is no net movement of water.

 

Water still moves in both directions across the membrane, but this occurs equally and results in no overall change in cell volume.

 

Exam rule: Equal osmolality → no net water movement

 

 

Why not the other options?

 

Net movement of water into the cell: This would require the extracellular fluid to have a lower osmolality.

 

Net movement of water out of the cell: This would require the extracellular fluid to have a higher osmolality.

 

Continuous unidirectional movement of water: Water moves in both directions at equilibrium, not one direction.

 

Active transport of water across the membrane: Water movement in osmosis is passive and does not require ATP.