Question 9

Water moves out of the onion cells.

The plasma membranes of onion cells shrink away from the cell walls when placed in a 5% table salt solution due to the net movement of water out of the cells.

A) water into the onion cells

This option is incorrect because when the onion cells are placed in a hypertonic solution such as a 5% salt solution, water does not move into the cells; rather, it moves out. If water were to move into the cells, the cells would swell rather than shrink.

B) water out of the onion cells

This option is correct as it accurately describes the process that occurs when onion cells are placed in a hypertonic solution. The high concentration of salt outside the cells creates an osmotic gradient that leads to water moving out of the cells, causing them to lose turgor pressure and shrink away from the cell wall.

C) salt into the onion cells

This option is incorrect because salt does not move into the onion cells in this scenario. Instead, the concentration gradient causes water to exit the cells, while the salt concentration outside the cells is higher, preventing the influx of salt.

D) salt out of the onion cells

This option is also incorrect because there is no net movement of salt out of the onion cells in this context. The salt concentration outside the cells is higher, leading to the movement of water out of the cells rather than salt.

Conclusion

The correct answer is B, as it explains the phenomenon of water moving out of onion cells when they are in a hypertonic solution, leading to cell shrinkage. All other options fail to account for the osmotic effects of the salt solution, demonstrating a misunderstanding of how water movement occurs in response to solute concentration gradients.