Final answer:
Potatoes in the ground can swell with water when it rains due to the process of osmosis. This happens if the water potential of the soil is less negative (higher) than that of the potatoes, causing water to move into the potato cells and causing them to swell.
Step-by-step explanation:
When potatoes are in the ground, they can swell with water when it rains, and this occurs due to a process called osmosis. Osmosis is the movement of water across a semi-permeable membrane from an area of low solute concentration to an area of high solute concentration. In this case, if the overall water potential of the potatoes is more negative compared to the surrounding soil (meaning the potato cells have a higher solute concentration), water will move into the cells of the potato, causing them to swell. This process allows plants to maintain turgor pressure, which is essential for their structural support and growth.
Moreover, plant cells have a rigid cell wall that protects them from bursting when they swell. This cell wall provides resistance against the osmotic pressure. With the right balance of water potential, potatoes can gain water without damage.
So the correct answer to whether potatoes swell with water when it rains would depend on the relative water potentials of the plant and the soil. If the soil's water potential is higher, meaning it is less negative than that of the potato (as in option a), the potatoes will swell as water moves into their cells due to osmosis.