Question

Osmosis causes water to move from areas of low salt concentration to areas of high salt concentration. The internal NaCl concentration of red blood cells is 0.9 M. The diagram below shows red blood cells submerged in solutions of four different NaCl concentrations—0 M, 0.65 M, 0.9 M, and 2 M. Which of the diagrams shows red blood cells in the 2 M solution?

Answer 1

You haven't given us the diagrams, but in case you're asking about the shape, imagine this: a disc, with a sunken centre, starting to resemble a donut.

In a low salt solution, the cells would start to absorb water, thus, inflating, up to the point of resembling spheres, and even bursting in the end. In case of a salty solution like the one you proposed, blood cells would lose water and would become a bit amorphous. In the attached pic you can see a standard blood cell (on the left), and a cell submerged in a salty solution (on the right).

Answer 2

Red blood cells normally have a biconcave shape (picture a donut, but instead of a hole through the centre there's just a downward slope to the centre of the cell). If the cell takes on water, it will increase in size and the sloped areas will start to flatten out. If the cell loses water, it will begin to shrivel. Use these observations and your understanding of osmosis to answer the question!