Question

A student measures the osmolality of two aqueous solutions, A and B. The student finds that the osmolality of solution B is much higher than solution A. Based on this result, how do solutions A and B likely differ in the concentration of solutes in their solution, and why?

a) Solution A has a higher concentration of solutes, promoting water movement out of cells.
b) Solution B has a higher concentration of solutes, promoting water movement into cells.
c) Solution A has a lower concentration of solutes, promoting water movement into cells.
d) Solution B has a lower concentration of solutes, promoting water movement out of cells.

Answer 1

Solution B has a higher osmolality and therefore a higher concentration of solutes than solution A, which makes it hypertonic and causes water to move out of cells when they are placed in solution B.

Step-by-step explanation:

The osmolality of a solution determines how water moves across a semipermeable membrane, such as the plasma membrane of a cell. When the student measures the osmolality and finds that solution B has a much higher osmolality than solution A, it indicates that solution B has a higher concentration of solutes. This causes water to move from areas of lower solute concentration (like within a cell, or solution A) to areas of higher solute concentration (solution B) to balance the solute concentration on both sides of the membrane.

A solution with higher osmolality is referred to as hypertonic, meaning that it has more solutes compared to the inside of the cell. Conversely, a solution with lower osmolality is known as hypotonic, and it has fewer solutes relative to the cell interior. When a cell is placed in a hypertonic solution like solution B, water is expected to move out of the cell, while in hypotonic situations, water moves into the cell.