ATI TEAS (Test of Essential Academic Skills) Version 7ScienceMedium
A biologist is studying the movement of water across a semipermeable membrane in a laboratory setting. They observe that water molecules are moving from an area of high water concentration to an area of low water concentration, without the cell expending any energy. What biological process is being observed?
- APinocytosis
- BOsmosis
- CActive transport
- DFacilitated diffusion
Show answer & explanationAnswer & explanation
Correct answer: B. Osmosis
Osmosis is the passive movement of water molecules across a semipermeable membrane from a region of higher water concentration (lower solute concentration) to a region of lower water concentration (higher solute concentration), requiring no cellular energy.
Why the other options are wrong
- A. Pinocytosis is a type of active transport (endocytosis) involving the engulfment of fluid and solutes by the cell membrane.
- C. Active transport requires energy (ATP) to move substances against their concentration gradient.
- D. Facilitated diffusion uses transport proteins but still moves substances down their concentration gradient, usually for solutes, not just water.
Osmosis
The passive movement of water across a selectively permeable membrane from an area of higher water concentration (lower solute) to an area of lower water concentration (higher solute).
- A type of passive transport.
- Does not require cellular energy (ATP).
- Crucial for maintaining cell volume and fluid balance.
Memory trick: Oh, So Much Water Moves Slowly In!