Question

A student is investigating the effects of salt water on a terrestrial plant cell. She first views a plant cell under a microscope and observes that the cell appears turgid, with the plasma membrane pressed tightly against the cell wall. After adding a drop of salt water to the slide, the student notices changes in the cell. She makes notes on her investigation that address:



1. How the plant cell has changed.

2. Why the plant cell has changed.

3. How the plant cell can be returned to homeostasis.



Which set of notes did the student MOST LIKLEY make?



A.
1. The cell’s plasma membrane pulled away from the cell wall.

2. Water has moved out of the cell by osmosis into a hypertonic salt water environment.

3. Placing the cell into pure water would reverse osmosis, so water re-enters by passive transport to restore homeostasis.

B.
1. The cell increased its volume and forced the membrane against the cell wall.

2. It gained turgor pressure because active transport pumped water into the cytoplasm and against the membrane.

3. Placing the cell in fresh water would allow water to return by osmosis to restore the turgor pressure and homeostasis.

C.
1. The cell's membrane has lost most of its original shape and has a different size.

2. The cell lost turgor pressure because salt was moved out of the cytoplasm by passive transport, lowering solutes and water.

3. Placing the cell into fresh water would allow water to re-enter by the process of osmosis to restore turgor pressure and homeostasis.

D.
1. The cell became smaller and the space between the plasma membrane and cell wall increased.

2. The cell lost water because active transport moved salt into the cytoplasm, increasing its internal solute concentration.

3. Placing the cell in pure water would stop the active transport of salt and allow water to re‑enter by osmosis to restore homeostasis.

Answer 1

Answer: A.

Why: Adding salt water creates a hypertonic environment so water leaves the plant cell by osmosis. The loss of water causes the vacuole and cytoplasm to shrink and the plasma membrane to pull away from the cell wall (plasmolysis). Returning the cell to pure (or much less salty) water makes the environment hypotonic relative to the cytoplasm so water passively re-enters by osmosis and turgor is restored.

(Note: option A’s phrase “reverse osmosis” is a bit misleading — the recovery is simply osmotic water influx, a passive process, not the engineered process called reverse osmosis.)