|Unit 3 Lab
Today you will:
Observe plant, animal, protist and bacterial cells.
Be able to identify cellular structures (membrane, nucleus, etc)
Advice: Do not rush through this lab!
Part I. Observations of Plant Cells
First, become familiar with the cellular structure of a leaf of Elodea, a water plant, by studying a prepared slide. The leaf has many layers of cells, especially in the thickest central part of the leaf. When many layers of cells overlap, the details of small structures within each cell become hidden. Therefore, it is most important for you to find cells near the edge of the leaf. Choose cells that are large and easy for you to observe clearly.
Make a hypothesis sketch what you think the plant cell will look like.
Wet Mount: Get a leaf of living Elodea. Choose one of the youngest (smallest) leaves from a sprig of Elodea. Make sure that the leaf is bright green and has thin, almost see-through edges. Tear one leaf off the Elodea, tear it in half, and place it on a clean microscope slide. Add 1-2 drops of water to the leaf and place one cover glass on top of the leaf. BE CAREFUL, cover glasses tend to stick together. If you have two cover glasses stuck together you will not be able to use the 100x objective on your specimen.
Examine the wet mount slide of Elodea, first using the 4x, objective, then with the 10x, and then the 40x. Notice that there are many different layers of cells present.
At each level of the microscope (4x, 10x and 40x) make a drawing of 2 cells. Make sure to identify chloroplasts and cell walls.
Analyze the Data
Do the cells look like the plant cells that you see in the textbook? Why or why not?
What is the benefit of being able to see the cells with higher magnification?
An Elodea Cell. (A) Upper surface of the cell (B) Middle of the cell. The disk-shaped things are chloroplasts located in the cytoplasm along the cell wall. Notice the lack of chloroplasts in the center of the cell which is the vacuole.
An Elodea Cell. (C) Middle of the cell, higher magnification than A and B
Below: Representative cheek cells after Methylene Blue staining.
Part II. Observations of Animal Cells Unstained
A. The Human Cheek Cell
Make a Hypothesis What do you think your cheek cells will look like? Make a sketch.
Prepare a wet mount of your cheek cells:
1. Put a drop of water on a slide.
2. Gently scrape the inside of your cheek with the flat side of a toothpick. Scrape lightly.
3. Stir the end of the toothpick into the water and throw the toothpick away.
4. Place a coverslip onto the slide. (put one edge of the coverslip on the slide and then gently drop the other edge into place.
5. Locate cells under low power (10x). Cells may be hard to see, but they can be found. Make sure to use the adjustment knob.
6. Once you think you have located a cell, switch to high power. (Remember, do NOT use the coarse adjustment knob).
Sketch two cells. Make sure to label the cell membrane and the nucleus.
How are the elodea cells and the cheek cells different? Make sure you answer the question in words and use pictures to further explain the answers.
Part II. Observations of Animal Cells Stained
Make a Hypothesis What do you think your cheek cells will look like with stain? Make a sketch.
Prepare a wet mount of your cheek cells, with stain:
1. Put two drops of water on a slide. See Ms. Cornick to have a drop of methylene blue (0.2%) put on a new slide. Caution: methylene blue will stain clothes and skin. Put two drops of water on the slide too.
2. Again, gently scrape the inside of your cheek with the flat side of a toothpick and stir the end of the toothpick into the stain and throw the toothpick away.
3. Place a coverslip onto the slide.
4. Switch to low power (10x). Cells should be visible, but they will be small and look like nearly clear purplish blobs. If you are looking at something dark purple, it is probably not a cell.
5. Once you think you have located a cell, switch to high power.
Sketch at least two cells. Label the nucleus, cytoplasm, and cell membrane.
Analyze the data
What did the stain allow you to do? Did the cells look like the animal cells in the textbook?
Wash off all slides and coverslips. Clean up your work area!