Questions and Answers
What is the best explanation for the color change that occurred inside the 'cell'?
The iodine diffused into the 'cell' and changed the starch to blue-black.
Did any starch diffuse out of the 'cell'? Explain how you can tell.
No. The iodine didn't change color to blue-black.
Did any glucose diffuse out of the 'cell'? Explain how you can tell.
Yes. When a sample of the liquid outside the 'cell' was mixed with glucose indicator (Benedict Solution) and heated, it changed color to brick-red.
Which substance(s) diffused through the membrane?
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Which substance(s) did not diffuse through the membrane?
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Explain why some substances were able to pass through the membrane while others were not able to.
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Describe the changes observed in the red onion cells after you added salt solution.
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Describe what happens to the water content of the red onion cells when they are placed in a salt solution.
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Describe the changes that occurred in the red onion cells after adding more water.
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During part 1 of this laboratory activity, one group of students followed the directions incorrectly. State how their results would differ from those obtained by students in their class who followed the directions correctly.
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Some state roads are salted heavily in the 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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When a person in the hospital is given an I.V., the fluid is typically a salt solution with about the same water concentration as human body tissues. Explain how the use of distilled water in place of this salt solution would be expected to upset the patient's homeostasis.
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Explain why contractile vacuoles would be of little value to one-celled organisms living in the ocean (salt water).
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Describe in scientific terms why salty popcorn causes thirst.
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Based on what you learned in this lab activity, explain why the digestion of starch to glucose is necessary.
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What is the Glucose Indicator Solution and the Starch Indicator Solution and what are their original colors?
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What is a hypotonic solution?
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What is a hypertonic solution?
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What is osmosis?
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What is an isotonic solution?
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Study Notes
Diffusion Through a Membrane Lab
- Iodine diffuses into the "cell," converting starch to blue-black, indicating a chemical reaction.
- Starch does not diffuse out of the "cell," supported by iodine not changing color outside the cell.
- Glucose diffuses out of the "cell"; tested by mixing with Benedict's solution, which changes to brick-red upon heating.
- Substances that diffused through the membrane: iodine (into the cell) and glucose (out of the cell).
- Starch does not pass through the membrane due to its large size.
- Semi-permeable membranes selectively allow small molecules to pass while blocking larger ones, like starch.
- Red onion cells shrink in salt solution as the cell membrane pulls away from the cell wall due to water loss.
- Water exits red onion cells in salt solution, causing a decrease in cell volume.
- Adding water to red onion cells results in cells swelling and contents expanding as water diffuses back in.
- Incorrect experimental setup with iodine and starch solution results in opposite color outcomes compared to correct procedures.
- High levels of salt on roadways lead to dehydration in organisms due to osmotic water loss from cells.
- Using distilled water for IV fluids can cause blood cells to swell and potentially burst due to osmotic pressure.
- Contractile vacuoles are less useful for saltwater organisms as osmotic balance is maintained passively through concentration differences.
- Salty popcorn induces thirst because salt creates a hypertonic solution in saliva, drawing water out of cells in the mouth.
- Starch digestion to glucose is essential as starch molecules are too large to diffuse across cell membranes, while glucose can easily pass.
- Glucose Indicator (Benedict Solution) is originally blue, while Starch Indicator (Iodine/Lugol's) starts amber.
- Hypotonic solutions have a lower concentration of water outside than inside, causing cells to swell.
- Hypertonic solutions have a higher concentration of water inside the cell compared to outside, leading to cell dehydration.
- Osmosis is the movement of water from areas of high concentration to areas of low concentration.
- Isotonic solutions maintain equal water concentrations inside and outside the cell, promoting cellular equilibrium.
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Test your understanding of diffusion processes through a membrane with these flashcards. Each card focuses on key concepts, such as the behavior of iodine, starch, and glucose during the diffusion experiment. Perfect for reinforcing your lab knowledge!
