Quiz

Diffusion, Osmosis and Cell Membranes

Quiz

Diffusion

The movement of molecules from a region of high concentration to a region of low concentration that is due to the random movement of the molecules.

Dynamic equilibrium

A state that occurs when the rate of two opposing processes is the same

Semipermeable membrane

A membrane that allows some molecules to pass through but not others, usually as a result of the size of the molecules or their charge.

Passive transport

The movement of materials into or out of a cell that does not require the use of energy by the cell.

II.

a. The level of the water and iodine solution will fall as more water moves into the starch solution than leaves it.

b. The level of the starch solution will rise since more water molecules will enter the solution than will leave it.

c. The water will move in both directions across the membrane.

d. The color of the water and iodine solution will not change since starch cannot pass through the membrane to enter the solution.

e. The color of the starch solution will turn from clear to a blue-black as iodine molecules cross the membrane, enter the solution and complex with the starch molecules.

f. Five (5) grams of starch will be present in 100 grams of a 5% starch solution.

III.

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.

IV.

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

Each of the definitions in Part I will carry a maximum value of one point. In order to earn full credit, the student must give a thorough definition in complete sentences. The responses to the questions in Part II will each be worth two points: one point for the correct response and one for the correct explanation. The questions in Parts III and IV will each be worth three points, and will be graded for evidence of an understanding of the concepts and on the logic of the argument.

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.

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The University of Arizona
Department of Biochemistry and Molecular Biophysics
General Biology Program for Secondary Teachers
warder@email.arizona.edu