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Review of NYS LabDiffusion and Membranes

Adapted from materials created by Mike Comet

Name: ___________________

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Part 1- Diffusion through a Membrane

• Diffusion

• Osmosis

• Selectively permeable

• Hypertonic

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Part 1- Diffusion through a Membrane

• Isotonic

• Hypotonic

• Saline

• Molecule size

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1. What does the tubing represent?

2. What substances did you pour inside of the tubing?

Part 1- Diffusion through a Membrane

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3. What was added to make the liquid outside the “cell” amber colored?

Part 1- Diffusion through a Membrane

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4. Why does the inside of the “cell” turn purple or black?

Part 1- Diffusion through a Membrane

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5. Did starch move from inside the cell to outside the cell? Explain how you know.

Part 1- Diffusion through a Membrane

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6. Did glucose move from inside the cell to outside the cell? Explain how you know.

Part 1- Diffusion through a Membrane

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Part 1- Diffusion through a Membrane

Describe the test for the presence of starch in a sample.

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Part 1- Diffusion through a Membrane

Describe the test for glucose in a sample.

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7. After placing 10 drops of the amber solution into a test tube, what do we add to it?

Part 1- Diffusion through a Membrane

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8. After adding the glucose indicator solution (blue) what do we do with the test tube?

Part 1- Diffusion through a Membrane

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9. If there is glucose in the solution, what will happen to the blue color after heating the tube for 2-3 minutes?

Part 1- Diffusion through a Membrane

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10. The blue color changed to orange. This means that what substance is in the test tube?

Part 1- Diffusion through a Membrane

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11. Glucose indicator solution was added to these test tubes, and then the tubes were heated. Which will change color?

starch glucose C6H12O6

Part 1- Diffusion through a Membrane

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Analysis Questions

• What substance(s) diffused through the membrane?

• 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.

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Analysis Questions

• Explain why some substances were able to pass through the membrane while others were not able to.

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Analysis Questions

Initial State Final State (after 20 minutes)

In both diagrams above, using letters “I” (starch indicator), “G” for Glucose, and “S” for starch, indicate the areas where each of these molecules are located.

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Part 2 - Osmosis

1. Why do you think we used red onions for this experiment?

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Part 2 - Osmosis

2. How do you prepare a wet mount for microscope examination of a sample?

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Part 2 - Osmosis

Onion cell at 400x in a isotonic solution

• Label the cell wall, cell membrane, cytoplasm

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Part 2 - Osmosis

Onion cell at 400x in a hypertonic solution

4. Explain the change observed in the cell.

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Part 2 - Osmosis

Onion cell at 400x after distilled water was added following the salt solution

5. Explain the change observed in the cell.

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Analysis Questions

• What test would you need to perform to prove it is the combination of glucose and the Glucose Indicator Solution that changes color when heated and not just the glucose or the Glucose Indicator Solution alone? Support your answer with an explanation.

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Analysis Questions

• During Part 1 of this laboratory activity, one group of students poured starch indicator solution in the “cell” and filled the beaker with starch and glucose solution. State how their results would be different than a group of students who followed the direction carefully.

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Analysis Questions

• Some state roads are slated heavily in winter, creating an environmental problem. Based on observations you made in this lab activity, explain how organisms could be harmed by high levels of salt from roadways.

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Analysis Questions

• When a person in the hospital is given fluid intravenously (an I.V.), the fluid id 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 the saline solution would be expected to upset the patient’s homeostasis. Your answer should refer to the process of diffusion.

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Analysis Questions

• 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 of little value to one-celled organisms living in the ocean (salt water).

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Controlling water• Contractile vacuole in Paramecium

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Analysis Questions

• Popcorn sold at most movie theaters is very salty, causing people to become thirsty and buy soft drinks. Based on what you learned in this lab, explain why the salty popcorn causes this thirst.

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Analysis Questions

• In many animals, glucose, rather than starch is transported by the blood through the body to all of the cells. Starches in many foods are digested to yield glucose. Based on what you learned in this activity, explain why the digestion of starch to glucose is necessary.