Plasma Membrane (Diffusion, Osmosis) MCQs

Q1. A gardener forgets a bunch of fresh spinach leaves on the kitchen counter and they turn limp and wilted by evening. Which process best explains why the leaves lost their crispness?

• A.Loss of water from the cells by osmosis to the drier surroundings
• B.Active transport of salts out of the leaf cells
• C.Diffusion of carbon dioxide into the leaf
• D.Gain of water by the cells from the air

Answer: A. Loss of water from the cells by osmosis to the drier surroundings

The air on the counter is drier (lower water concentration) than the cell sap. Water moves from the high water concentration inside the cells to the drier air by osmosis/evaporation, so the cells lose water, become flaccid, and the leaf wilts.

Q2. A cook sprinkles plenty of salt over freshly cut cucumber slices and notices a pool of water collecting around them after some minutes. What causes this water to come out of the cucumber?

• A.Water evaporates from the cut surface
• B.The cells actively secrete water using energy
• C.Salt diffuses into the cucumber and pushes water out
• D.Water leaves the cucumber cells by osmosis into the salty surroundings

Answer: D. Water leaves the cucumber cells by osmosis into the salty surroundings

Salt outside makes the surrounding solution hypertonic (less water) compared with the cell sap. Water therefore moves out of the cucumber cells through the membrane by osmosis, collecting as a visible pool.

Q3. Dry raisins are dropped into a bowl of plain water and after a few hours they have swollen up and become plump. Which statement correctly describes what happened at the cell level?

• A.Air trapped in the raisin expanded
• B.Water was actively pumped in by the raisin using energy
• C.Sugar from the raisin diffused into the water, swelling the raisin
• D.Water entered the raisin cells by osmosis because the cell contents were more concentrated than the water

Answer: D. Water entered the raisin cells by osmosis because the cell contents were more concentrated than the water

The dried raisin's cell contents are highly concentrated (little water). Plain water is more dilute, so water moves into the raisin cells through their membranes by osmosis, making the raisin swell and turn plump.