Questions: Question 4 of 25 A salmon moves from a saltwater ocean to a freshwater river. What takes place in the salmon's cells as it moves? A. The cells lose water because of the movement of water by osmosis. B. The cells remove salt to balance the solute concentration. C. The cells take in salt to balance the solute concentration. D. The cells fill with water because of the movement of water by osmosis.

The answer is D: The cells fill with water because of the movement of water by osmosis.

Explanation for each option:

A. The cells lose water because of the movement of water by osmosis.

• This option is incorrect. When the salmon moves from saltwater to freshwater, the surrounding environment becomes less salty (hypotonic compared to the cells). Therefore, water will move into the cells rather than out of them.

B. The cells remove salt to balance the solute concentration.

• This option is partially correct but not the primary process described in the question. While the salmon does have mechanisms to regulate salt concentration, the immediate effect of moving to freshwater is related to water movement by osmosis.

C. The cells take in salt to balance the solute concentration.

• This option is incorrect. In freshwater, the salmon's cells would not take in salt; instead, they would need to expel excess water and manage salt loss.

D. The cells fill with water because of the movement of water by osmosis.

• This option is correct. When the salmon moves to a freshwater environment, the surrounding water is less concentrated with solutes compared to the inside of the cells. This causes water to move into the cells by osmosis, leading to the cells filling with water.

Summary: When a salmon moves from a saltwater ocean to a freshwater river, its cells fill with water because of the movement of water by osmosis. This is due to the freshwater environment being hypotonic relative to the cells, causing water to enter the cells.