Question 37

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 onion cells.

A) water into the onion cells

This option is incorrect because the scenario describes a hypertonic solution (5% salt) surrounding the onion cells. In such a situation, water does not move into the cells; instead, it moves out to balance the solute concentration.

B) water out of the onion cells

This option is correct. The presence of a higher concentration of salt outside the onion cells creates a concentration gradient, leading to the net movement of water out of the cells. This causes the plasma membranes to shrink away from the cell walls, a process known as plasmolysis.

C) salt into the onion cells

This option is incorrect. While salt does enter the cells to some extent, the primary movement that causes the plasmolysis effect described is the movement of water out of the cells. The salt concentration outside the cells is higher, which does not favor the movement of salt into the cells.

D) salt out of the onion cells

This option is also incorrect. The salt concentration outside the cells is greater than inside, so there is no significant movement of salt out of the onion cells. The primary movement occurring is water leaving the cells, not salt.

Conclusion

In summary, option B is the definitive correct answer as it accurately describes the movement of water out of the onion cells when exposed to a hypertonic solution. All other options fail to capture the essential process of osmosis that leads to the observed plasmolysis effect in this context.