Diffusion, Osmosis and
If a person were given an intravenous injection of pure water, the concentration of the water in the serum of the blood would be higher than in the red blood cells. More water would flow into the cell than out of the cell, causing it to swell. Since the cell membrane is not permeable to most of the other molecules in the cell, the cell would be unable to prevent the swelling and might burst. Should this happen on a large scale it would be dangerous for the person.
The support mechanism for a plant consists of the cell walls. In plants (like most houseplants) with green stems, the cell walls of the stems are relatively thin and flexible. When the cell is full of water, it presses against the cell wall and makes it more rigid. If the plant lacks sufficient water, the cells shrink, and the pressure against the cells walls is reduced. This allows the cell walls to bend, so that the stem is unable to support the leave, and the plant wilts.
When the cells are placed in tap water, both types retain their original shape. When the cells are placed in a salt or starch solution, both types will shrink, although the plant cell walls will not change shape. When the cells are placed distilled water, both types will swell. The plant cell will expand to the limits presented by the cell wall. The blood cell, having no cell wall, will swell until it bursts.
Evaluation of the Quiz
Point totals will be recorded as part of the overall grade for the term. The term grade will be determined relative to a percentage scale, with 90-100% of the points corresponding to a "A", etc.
The University of Arizona
Department of Biochemistry and Molecular Biophysics
General Biology Program for Secondary Teachers