1. to Observe Plasmolysis in Anachris Plant Cells to Better Understand How Osmosis Works

Osmosis in Aqueous Plants - Plasmolysis

Biology

Objectives

1. To observe plasmolysis in Anachris plant cells to better understand how osmosis works.

2. To learn how aqueous (living in water) organisms deal with changing conditions in the environment around them.

Background

Osmosis is the process whereby water moves across a cell membrane by diffusion.

Diffusion takes place when the molecules of a substance tend to move from areas ofhigher concentration to areas of lower concentration. The process of osmosis must betightly controlled by cells, otherwise they will die. For example, if you place a red bloodcell in pure (distilled) water, it will quickly take up water until it bursts. That is whyplasma, the liquid portion of our blood is made of water with proteins and salts dissolvedin it, preventing the unnecessary gain of water by our blood cells.In plants, osmosis is just as important. Plants with too little water will wilt. This happenswhen water moves out of the cells by osmosis. Without this water there is little pressureinside the cells and the plant can no longer support itself against the pull of gravity.However, after watering the plant, the cells become reinflated with water and the plantstands upright. The effect of water loss on plant cells is shown in the diagram below.

Figure A. 1. Plant cell placed in pure water. This cell will become inflated because the water outside the cell is at ahigher concentration than the water inside the cell. As water moves in by osmosis the vacuole fills up and presses outagainst the cell wall. 2. The same cell in water equal to the concentration inside the cell. This cell has no overallgain or loss of water because whatever moves out will be replaced by water moving in. 3. A cell placed in a salt solution. This cell will lose water as the water moves by diffusion from higher to lower concentration. Thecytoplasm of this cell has shrunken in a process called plasmolysis. (The size of the symbols for water represent therelative concentration: larger symbol = more water.)

Materials:

1. 1 Anachris leave

2. Microscope

3. Microscope slide, cover slip, eye dropper

4. Solution A

5. Solution B

6. Solution C

Lab Procedures:

1. Remove a single leaf from an Elodea plant and place it on a microscope slide. Use a dropper to place a drop of Solution A on the leaf. Cover the leaf with a coverslip and place the slide under a microscope.

2. Focus on the leaf under high power (40x). Move the slide around to find an area where you can clearly see single cells. They willappear rectangular and look like green bricks in a wall. The illustration at right shows how they look. The green ovalsinside the cells are chloroplasts. After awhile you may seethem start to move around the cell.

3. Sketch a picture of 1 Anachris cell in Solution A at high power in the box below.

4. Leave the slide on the microscope. Using the dropper, place a drop of solution B on the

right edge of the coverslip. Place a small piece of paper towel on the left edge of the

coverslip. As solution A soaks into the paper towel it will draw solution B under the

coverslip. Repeat 1-2 times to ensure the new solution is all that remains under the coverslip. This is illustrated below.

5. Again, in the box below, sketch a picture of 1 Anachris cell at high power, now in solution B.

6. Again, in the box below, sketch a picture of 1 Anachris cell at high power, now in solution C.

7. Repeat Step 4 above, but this time replace Solution B with Solution C. Solution C will be drawn under the coverslip. To make sure all of Solution B is gone from under the coverslip, repeat this same thing one more time. Your cell should now look like it did in solution A. Observe your cell and make sure this is the case.

8. When you have finished, clean your slide and coverslip and return them to the front of class.

(Make sure your conclusion answers the following questions along with the other typical requirements!)

-The 3 solutions used during the experiment were Aquarium Water, Distilled Water, and a Salt Water solution. Based on your observations, what is Solution A? Solution B? Solution C? Why?

-In this experiment, which type of transport did you observe (passive or active)? Explain why.