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Topic 5 Diffusion, Osmosis, and Biological Membranes (questions from the book- General Biology Laboratory Manual Investigations Into Life's Phenomena

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The molecules of all matter, particularly gases and liquids, are in constant vibration motion. As a result of this motion, molecules are continually colliding with one another, much like balls scattering over a pool table. Using a microscope, you can observe these molecular collisions that produce the effects of diffusion and osmosis
1.Obtain a slide and place two drops of water on it. set the slide down on the table.
2.stick a toothpick vertically down into the container of carmine due powder to a depth of about one half inch. Hold the toothpick vertically over the water drop on your slide with point just above the water. Gently tap the toothpick to shake a light sprinkling of red dye powder into the water drop.
3.Add a coverslip over the drop of water. Place the slide on your microscope and observe under low and high power. carefully examine an area where the powder granules are evenly dispersed throughout the field of view. Note that the vibration motion of the red granules is caused by vibration water molecules colliding with each other and the powder granules.

1. When will an equilibrium be reached? Do the powder granules stop moving at equilibrium?

2. Predict how a change in medium ( that is, water to gelatin) would affect the rate of discussion?

Diffusion is the movement of a substance from a region of higher concentration to a region of lower concentration. It is facilitated by the molecular motion you observed in 5A. Several factors affect diffusion such as temperature and the molecular weights of the diffusing molecules.
1. Obtain two test tubes of equal size. Using a graduated cylinder, pour 10ml of cold tap water into one of the tubes. Pour 10ml of hot tap water in the other tube.
2.using forceps, add one crystal of potassium permanganate into each test tube. Without disturbing the tubes in anyway observe the diffusion of the purple potassium permanganate in both test tubes for 3mins.

1. In which test tube diffusion the greatest after three mins?

2. Knowing that diffusion is facilitated by molecular collisions, how does the temperature of the tube with greatest diffusion affect the molecular motion of the water and potassium permanganate?

3. With time, would the tube with least diffusion eventually reach the same state as the tube with greatest diffusion?

Plant cells are completely surrounded by a rigid cell wall. The plasma membrane lies just inside the cell wall. Water and all other materials that enter and leave the cell pass through the plasma membrane and cell wall.
1. Prepare a wet mount of an ELODEA leaf taken from the growing tip of a plant Place the slide on your microscope and observe under both low and high power.
2. Life the coverslip and place a few drops of 20% salt solution on the ELODEA leaf. REplace the coverslip and again examine the leaf cells under low and high power.

The difference in the appearance between normal and salt treated ELODEA cells is due to waterloss. THe water loss reduces the volume of the cells contents and the plasma membrane pulls away from the rigid cell wall as the cells shrinks. This process is known as plasmolysis.


1. By what process does water leave the salt-treated Elodea cells?

2. The 20% salt solution is hypertonic/hypotonic isotonic to the solute concentration of eldodea cells.

3. How would you reverse the process of plasmolysis in Elodea cells?

4.Compare the location of Chloroplasts in normal versus salt- treated Elodea cells. Why the Difference in locations?

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Lab 5A

1. When will an equilibrium be reached? Do the powder granules stop moving at equilibrium?

Equilibrium will be reached when there is no longer an observable concentration gradient anywhere in solution. That means that when the dye particles have evenly distributed themselves throughout the water, there will be equilibrium. However, just because equilibrium has been reached doesn't mean that the particles will stop moving. Remember, there is always vibrational energy in molecules even when systems are at equilibrium.

2. Predict how a change in medium (that is, water to gelation) would affect the rate of diffusion?

In this case, the rate of diffusion would be affected by the viscosity of the medium. What does "viscosity" mean? It is a measurement of the degree of "thickness" of a liquid. Oil is more viscous than water. A gelatinous solution would be more viscous than water. Therefore, if the solution is thicker and less fluid (more viscous), then we would expect that the rate of diffusion rate would slow down. Does this make sense to you? Think about it. The thicker the solution, the less fluid the solution; therefore, the harder it is for particles to move around in it, and the slower the diffusion rate.

Lab 5B

1. In which test tube was ...