Protocol osmosis - Procedure and questions made for lab report PDF

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Procedure and questions made for lab report...

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Introduction to Osmosis I. What is happening to these eggs? Each cell is surrounded by a cell membrane that regulates what gets into and out of the cell. The cell membrane allows some small molecules like water and oxygen to cross, but prevents many types of molecules from crossing the membrane. 1. This type of membrane is called a selectively permeable membrane. Explain why “selectively permeable” is a good way to describe a cell membrane.

2. Why is it important for each cell to be surrounded by a cell membrane that prevents large molecules from leaving the cell?

You will investigate which way water moves across a selectively permeable membrane, depending on the type of liquid surrounding a cell. Most cells are tiny – much too small to see without the help of a microscope. In contrast, an unfertilized chicken egg contains a giant cell surrounded by a selectively permeable membrane. You will use chicken eggs for your investigation. Your group will be given two eggs. To begin, record the weight and/or circumference of each egg in the day 1 row of the table. (Measure the circumference around the widest part, not lengthwise.)

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Caution: Because these are raw eggs, they may carry salmonella, so you should use gloves when handling the eggs. Egg 1 Day Weight (grams)

Egg 2 Circumference (cm)

Weight (grams)

1

2

(with shell) Egg put into vinegar (most of shell

(with shell) Egg put into vinegar (most of shell

Circumference (cm)

removed) Egg put into water

removed) Egg put into corn syrup

3

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Put each egg in a container labeled Egg 1 or Egg 2 with enough vinegar to cover the egg. Cover the container. Do you see bubbles forming around the egg? These are bubbles of CO which result from the chemical reaction between the acetic acid in the vinegar and the calcium carbonate in the eggshell. This reaction will dissolve most of the eggshell by day 2. 2

Day 2  Observe your eggs. Notice that most of the shell has been dissolved by the acetic acid in the vinegar. Although most of the shell is gone, each egg is still surrounded by a shell membrane. The shell membrane has protein fibers that give it much greater strength than a cell membrane. However, the egg without its shell is still fragile, so you will need to handle your eggs very gently and carefully! 

Rinse and dry each egg and measure the weight and/or circumference of each egg. Record your results for day 2 in the table on page 1.

3a. Did the eggs became ___ heavier/larger or ___ lighter/smaller? 3b. What do you think happened to cause this change in weight/size?

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Empty the vinegar from the container for egg 1, rinse the container and add water to cover the egg.

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Empty the vinegar from the container for egg 2, rinse the container and add corn syrup to cover the egg. As you pour the corn syrup, notice that it is viscous (thick, sticky).

4. What do you think causes the corn syrup to be so viscous?

Day 3

5. Compare and contrast the appearance of the egg that has been in water vs. the egg that has been in corn syrup.

6. You may be able to see a layer of water on top of the corn syrup. Where do you think this water came from?

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Rinse the corn syrup off of egg 2. Dry each egg and measure and record the weight and/or circumference for day 3 in the table on page 1.

7. What do you think happened to cause the change in weight/size of the egg placed in corn syrup?

8. Why did the egg placed in water get bigger and heavier? Where do you think the additional weight/volume came from? II. Osmosis – Effects on Animal and Plant Cells As you know, the cell membrane is a selectively permeable membrane. This figure shows a selectively permeable membrane that allows water molecules to cross, but not solute molecules. Water molecules cross a selectively permeable membrane in both directions, but more water molecules move from the solution with a lower concentra

tion of solutes to the solution with a higher concentra tion of solutes. 9a. Which side has the higher concentration of solutes? ___ left side ___ right side 9b. Draw an arrow to show which direction more water molecules will move across this selectively permeable membrane. There will be a net movement of water from the solution with a lower concentration of solutes to the solution with a higher concentration of solutes. This net movement of water across a selectively permeable membrane is called osmosis. 10. Inside the cell membrane, each cell contains cytosol, a watery substance that has a relatively high concentratio n of solutes (dissolved

molecules and ions). The cell in this figure is surrounded by pure water. Draw an arrow to show whether there will be net movement of water into the cell or out of the cell. Explain your reasoning. This figure shows the effects of

A

B

C

osmosis on animal and plant cells that were put in three different types of surrounding fluid. 11a. Which of these diagrams shows the expected effect of putting a cell in very salty water which has a higher concentration of solutes than cytosol? ____ 11b. Explain your reasoning.

12a. Which animal cell in this figure looks like the egg in corn syrup? ____ 12b. Based on the results of the egg experiment, which has a higher concentration of solutes? ___ the contents of the egg ___ corn syrup 12c. How do you know?

13. Most animal cells are surrounded by a layer of water with dissolved substances. For animal cells to function normally, there should be equal amounts of water moving into and out of the cell, as

shown in figure B. Which type of surrounding fluid would result in equal amounts of water moving into and out of a cell? ___ water with a higher concentration of solutes than the cytosol ___ water with a lower concentration of solutes than the cytosol ___ water with the same concentration of solutes as the cytosol 14. Which animal cell looks like what could have happened to the egg in water, if the egg didn't have a strong shell membrane around it? ____ 15a. In figure C, why does the animal cell burst, but the plant cell does not?

15b. Suppose that the cells in animals had cell walls. What problems would this cause for animals?

Challenge Questions A. If a person drinks a very large amount of water in a short time without consuming any salt, this can result in confusion, seizures, coma, or even death, due to abnormal functioning of nerve cells in the brain. Explain how these problems could result from drinking too much water too quickly.

B. Some archaea (which are single cell organisms) live in extremely salty water such as the Great Salt Lake or the Dead Sea. Most types of cells would shrivel and die in this very salty water. How do you think these archaea cells prevent water loss while living in very salty water?...