Describe these cells in relation to the solution surrounding them. What do you expect to happen to each cell? Which cell will need to use the most energy to run its Na+/K+ ATPase? Why?

Cells A and B are hyperosmotic to the solution and will swell. Cell C is hypoosmotic to the solution and will shrink. Cell B is most hyperosmotic, so it will have the most water entering it by osmosis. It will have to use its Na+/K+ pump the most to move the water back out.

A woman was scheduled for brain surgery, so the doctors wanted to dehydrate her beforehand. They gave her a solute called mannitol, which filtered into her urine. As a result, she produced a lot of urine and became mildly dehydrated. She complained of a dry mouth and thirst.

How could the mannitol have caused her to urinate so much? Draw a diagram comparing her urine and blood and showing what has happened.

Mannitol enters the urine and makes it hyperosmotic to the blood. Now water will move from the blood into the urine and be carried out of the body.

What happened to her cells to cause her thirst? Is this normal, or should she be worried about it? As she became dehydrated, her blood became hyperosmolar to her cells. Water began to move out of the cells, making them shrink. This caused her thirst, which is normal.