Question

a student is planning an investigation to determine how the concentration of a solute in a solution affects osmosis and therefore cells. the student uses rat blood cells, which have an nacl concentration of 0.9% when they are in homeostasis. the steps of the investigation are described below.

• place a drop of blood on a microscope slide.
• view the blood under high magnification. record observations of the general shape and appearance of the blood cells.
• place a drop of 0.9% nacl solution on the slide. ensure it mixes with the blood sample.
• wait several minutes, and then view the slide under high magnification. record any observations.
• using new blood samples, repeat the two steps above using distilled water and 15% nacl solution instead of the 0.9% nacl solution.

which of the following is the best hypothesis for the students investigation?
a the cells will stay the same size in the 0.9% nacl solution, swell in distilled water, and shrink in the 15% nacl solution.
b the cells will shrink in distilled water, stay the same size in the 0.9% nacl solution, and swell in the 15% nacl solution.
c the cells will swell in the distilled water and in the 15% nacl solution, but they will stay the same size in the 0.9% nacl solution.
d the cells will stay the same size in distilled water and in the 0.9% nacl solution, but they will swell in the 15% nacl solution.

Explanation:

Osmosis is the movement of water across a semi - permeable membrane from an area of lower solute concentration to an area of higher solute concentration. Rat blood cells have an internal NaCl concentration of 0.9%. In a 0.9% NaCl solution, it is isotonic to the cells, so water movement in and out is balanced and cell size stays the same. Distilled water has a lower solute concentration (hypotonic) compared to the cells, so water will move into the cells causing them to swell. A 15% NaCl solution is hypertonic compared to the cells, so water will move out of the cells causing them to shrink.

Answer:

A. The cells will stay the same size in the 0.9% NaCl solution, swell in distilled water, and shrink in the 15% NaCl solution.