Diffusion Through a Membrane Test

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Biology Test on 10/4/12

What is the best explanation for the color change that occurred inside the "cell"?

The iodine diffused into the "cell" and changed the starch a different color.

Did any starch diffuse out of the "cell"? Explain how you can tell.

No because the iodine didn't change any colors.

Did any glucose diffuse out of the "cell"? Explain how you can tell.

Yes because the glucose indicator (Benedict Solution) changed color.

Which substabce(s) diffused though the membrane?

Iodine (went in) & Glucose (went out)

Which substance(s) did not diffuse through the membrane?

starch

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

Only some substances were able to pass through because the cell is semipermiale and will only let certain substances pass through. The membrance will allow small particles to pass through, while large molecules, such as starch, cannot.

Describe the changes observed in the red onion cells after you added salt solution.

The cell contents shrunk away from the cell wall.

Describe what happens to the water content of the red onion cells when they are placed in a salt solution.

The water moved out of the cell (or the vacuole inside the cells) causing the cells to decrease in volume. (salt sucks)

Describe the changes that ocurred in the red onion cells after adding more water.

The cells got larger and the contents expanded as water diffused back into the cell.

During part 1 of this laboratory activity, one group of students followed the directions incorrectly. They poured the Starch Indicator (Iodine) 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 he directions correctly.

The incorrect group's beaker would be a dark color and the cell would be amber, while the correct groups' will be the opposite.

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

Organisms can be harmed because the salt will suck the water from the organisms or plants on the road, killing or damaging them.

When a person in the hopsital 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 set the patient's homeostasis.

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.

Explain why contractile vacuoles would be litle value to one-celled organisms living in the ocean (salt water).

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 concentration of the water in the cells, so there is no excess water to be removed.

Describe in scientific terms why salty popcorn causes thirst.

The salt may cause water to leave the cells of the mouth and throught due to diffusion. This causes the person to be thirsty.

Based on what you learned in this lab activity, explain why the digestion of starch to glucose is necessary.

Starch must be digested because its molecules are too large to diffuse across cell membrances. The starch would not be able to diffuse from the intestine into the blood and from the blood into the cells, Glucose is so small and soluble, so its able to diffuse.

What is the Glucose Indicator Solution and the Starch Indicator Solution and what are their original colors?

Glucose Indicator-Benedict Solution (blue)
Starch Indicator-Iodine (amber)

Hypotonic

less solutes dissolved in water-"weak"

Hypertonic

a lot of solutes dissolved in water-"strong"

Osmosis

the passag of water from an area where there is more water molecules to an area where there is less water molecules

Isotonic

when the concentration of 2 solutions are the same

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