Osmosis in Living Cells

Name: ______Period: ______

Osmosis in Living Cells

Problem: How do changes in a plant cell’s environment affect the cells?

Briefly read the procedure and then write a hypothesis statement that could be tested by the experiment described.

Your hypothesis:

Materials:

·  Elodea plant leaves

·  microscope

·  paper towels

·  eye dropper

·  5% salt solution

·  10% salt solution

Procedure:

1.  Pluck a healthy (bright green) leaf from the elodea plant. Break the leaf into two or three pieces (share the leftover piece with a partner) and make a wet mount slide as shown previously by your instructor. Be sure to use the water that the leaf was already in as part of the mount, not tap water.

2.  Locate a few clearly visible cells with the low power lens and then carefully switch to the high power lens. The leaves are relatively thick so you must be extra careful when focusing on high power. Draw a cell or two with as much detail as possible in the space provided. Use color if you wish.

3.  Remove the slide from the microscope. Lift the edge of the coverslip up and put a couple of drops of 5% salt solution on the leaf. Replace the coverslip and wipe up any extra salt water that leaks out with a paper towel before returning the slide to the scope. Starting on low power again, find a few cells, switch carefully to high power. In the space provided, draw the cell as it appears in the 5% solution.

4.  Make a new wet mount slide using 10% salt solution instead of the 5% solution. You can reuse the leaf or get a new one, but you should get a new coverslip and wipe up excess solution that leaks out. Salt water tends to make the coverslips cloudy and makes observing cells with a microscope difficult. In the space provided, draw the cell as it appears in the 10% solution.

5.  Clean up COMPLETELY before answering the questions that follow. Discard the leaf in the trash, put the used coverslip in the glass container, wipe off the slide and return it to the box. Wipe off all salt water from your microscope and return it to the cart.

Cells in aquarium water Cells in 5% salt water Cell in 10% salt water

Analysis Questions

1.  Describe the change in the cell’s appearance from plain water to 5% to 10% salt solutions.

2.  Make a conclusion statement based on your hypothesis and your resulting observations.

3.  How do you think the original water the cell was growing in compares to the cell’s cytoplasm (i.e. is it hypotonic, isotonic or hypertonic)? Explain how you know.

4.  How do you think the concentration of each salt solution compares to the cell’s cytoplasm? Explain how you know.

5.  Describe the effect on each cell if you placed plant and animal cells in distilled water (remember that plant cells have a tough cell wall and animal cells have only the membrane).

6.  Based on what you observed in this lab, describe what happens to plant cells during a light frost—hint: after a frost plant leaves usually wilt (droop).