Diffusion through the Membrane

1. Diffusion through the Membrane

2. Questions – Pg 2 #9 – Based on your knowledge of diffusion, predict what will happen to the substances inside and outside of the ‘cell’. Record your prediction. A: I predict that the glucose will move out of the ‘cell’ and may predict that starch will move out too.

3. Questions – Pg 3 • Table Two – Chemical Test Results: Green, Brown, Red or Orange Blue Blue Amber Blue-Black Amber

4. Questions – Pg 3 • What test would you need to perform to prove that it is the combination of glucose and the Glucose Indicator Solution that changes color when heated and not just the glucose or the GlucoseIndicator Solution alone? Support your answer with an explanation. A: You would need to heat a clean test tube of the Glucose Indicator Solution by itselfand another test tube of the glucose by itself. Then you would heat the solutions by themselves to provide evidence whether or not either of them change color when heated.

5. Questions – Pg 4 • Record any changes, including color changes, you observe in the ‘cell’ and in the beaker. A: I observed a change in the color of the ‘cell’ (from colorless or milky white to blue-black).

6. Questions – pg 4 • Label the contents and note the colors present in both beaker and the cell of the ‘Final State’ diagram below.

7. Questions – pg 4 • What is the best explanation for the color change that occurred inside the ‘cell’? • Did any starch diffuse out of the ‘cell’? Explain how you can tell. A: Iodine diffuses into the ‘cell’ causing the starch to change colors. No A: The contents of the beaker (containing Starch Indicator Solution) did not change color.

8. Questions – Pg 4 • Did any glucose diffuse out of the ‘cell’? Explain how you can tell. • Which substance(s) diffused through the membrane. Yes A: When the water surrounding the ‘cell’ was tested after 20 minutes, the result was positive. A: Iodine (Starch Indicator Solution) and glucose. Water also diffused across the membrane.

9. Questions – Pg 4 • What substance(s) did not diffuse through the membrane? • Explain why some substances were able to pass through the membrane while others were not able to. Starch A: The membrane would allow small particles to pass through. Large particles such as starch could not pass through.

10. Questions – Pg 4 • In the ‘Initial State’ diagram below, Starch Indicator Solution is indicated by the letters ‘I’ because it contains iodine. Using the letters ‘S’ for starch and ‘G’ for glucose, indicate the areas where each of these molecules are located in both diagrams. Be sure you indicate the location of iodine molecules in the ‘Final State’ diagram too.

11. Questions – pg 7 • Based on your observations, draw and color a typical red onion cell mounted in water. Label the cell wall, cell membrane, and cytoplasm.

12. Questions – pg 7 • Observe the cells for several minutes. You should see a change in the cells from your previous observation. If not, add more salt solution. Describe the changes you observed in the red onion cells. A: The cell contents shrink away from the cell wall.

13. Questions – pg 7 • Based on your observations, draw and color a typical red onion cell mounted in salt solution. Label the cell wall, cell membrane and cytoplasm.

14. Questions – pg 7 • Describe what happens to the water content of the red onion cells when they are placed in a salt solution. • Observe the cells for several minutes. Describe the changes that occurred in the red onion cells. A: The water moved out of the cells (or the vacuole inside the cells), causing the cells to decrease in volume. A: The cell gets larger (contents expand) as water diffuses back in.

15. Questions – pg 7 • Based on your observations, draw and color a typical red onion cell mounted in distilled water. A: The cells begin to ‘recover’ from the water loss that occurred with the addition of the salt solution.

16. Analysis Questions – Pg 7 • During Part I of this laboratory activity, one group of students followed the directions incorrectly. They poured the Starch Indicator Solution into the ‘cell’ and filled the beaker with starch and glucose solution. State how their results would differ from those obtained by students in their class who followed the directions correctly. A: The color changes to blue-black would occur in the beaker, rather than within the cell.

17. Analysis questions – pg 8 • Some state roads are salted heavily in the winter, creating an environmental problem. Based on observations you made during this laboratory activity, explain how organisms could be harmed by high levels of salt from roadways. A: The salt could damage or kill the plants. Diffusion would cause the water inside the plant cells to leave the cells.

18. Analysis questions – pg 8 • When a person in the hospital is given fluid intravenously (an I.V.), it is typically a saline (salt) solution with about the same water concentration as human body tissues. Explain how the use of distilled water in place of this saline solution would be expected to upset the patient’s homeostasis. Your answer should refer to the process of diffusion A: The process of diffusion would cause water to enter the person’s blood cells, causing them to swell. This could lead to the destruction of the blood cells.

19. Analysis questions – pg 8 • Many fresh-water one-celled organisms have structures called contractile vacuoles. These structures collect and pump out excess water that accumulates in the cell. Name the process that causes water to flow into these organisms. . Explain why contractile vacuoles would be little value to one-celled organisms living in the ocean (salt water). A: Diffusion causes excess water to enter the cells of fresh-water organisms. The excess water must be removed. In salt water, the concentration of water outside is either the same as or less than the concentration of water in the cells, so there is no excess water to be removed.

20. Analysis questions – pg 8 • Popcorn sold at most movie theaters is very salty, causing people to become thirsty and buy soft drinks. Describe in scientific terms why the salty popcorn causes this thirst. You should mention changes in specific body cells in your answer. A: The salt may cause water to leave the cells of the mouth and throat due to diffusion. This causes a person to be thirsty.

21. Analysis questions – pg 8 • In many animals, glucose, rather than starch, is transported by the blood through the body to all the cells. Starches in many foods are digested to yield glucose. Based on what you learned in this laboratory activity, explain why the digestion of starch to glucose is necessary. A: Starch must be digested because its molecules are too large to diffuse across the cell membranes. The starch would not be able to diffuse from the intestine into the blood and from the blood into the cells. Glucose is small and soluble, so it is able to diffuse.