1. when potatoes are in the ground, do they swell with water when it rains? if not, how do you explain that. if so, what are the advantages or disadvantages in this adaptation?

Salutations! The answer you are looking for is: The actual potato only holds energy. The roots soak up the water and transfer the necessary nutrients to the food, rather than the potato gathering it directly. The potato may swell a little bit, however for the most part it isn't able to suction enough, nor does it need to. 

hope this helps