Procedure
Part A - Human Cheek Epithelium

Cheek epithelial cells line the inside of your mouth. They are fairly large, flat, and somewhat oval in shape. They do not have any pigments and therefore will need to be stained to be observed. The stain will bind to the nucleus inside the cell.

NOTE - due to COVID instructors may wish to assign a remote version of Part A. Click here to access the remote version

1. Place a small drop of tap water on a microscope slide.
2. Scrape the inside of your cheek gently (not so hard that you draw blood) with a flat toothpick and mix with the drop of water on the slide.
3. Add a SMALL drop of methylene blue stain and stir gently.
4. Cover with a cover slip by placing one edge of the cover slip at the edge of the drop and then slowly lowering it onto the sample.
5. Find cells by first using the scanning lens (4x) and then switching to the low-power objective (10x).
6. Switch to high power (40x). Observe the a squamous epithelial cells; they are flat like pancakes and transparent. The dark blue areas inside the cells are the nuclear material that has been stained with the methylene blue. The outer edge of the cell (cell membrane will stain a light blue. You will most likely see tiny bacterial cells on the surface of the epithelial cells that have also taken up the blue stain.
7. Draw and label a few representative cells in your Part A of your Lab Report.

Part B - Comparison of Human & Frog Blood

Blood is a mixture of fluid and cells. The cells in the blood sample are either red blood cells (RBC) or white blood cells (WBC). Red blood cells appear red in color due to hemoglobin, the oxygen carrying protein in red blood cells. In humans these cells lack a nucleus and a relatively short lived. White blood cells are a critical component of the immune system. They are larger than red blood cells and contain a nucleus. Some white blood cells contain several nuclei.

1. Obtain two prepared slides: human blood and frog blood.
2. As always begin with the scanning objective lens (4x) and work your way up to the high-power objective (40x). Observe both slides under the high-power lens.
3. On the human blood slide, observe the differences between the smaller red blood cells and the larger white blood cells. Notice the stained nuclei within the white blood cells. Notice the structural differences between the non-nucleated, oxygen-carrying red blood cells and the nucleated white blood cells that function in the immune system.
4. Observe the frog blood slide. Compare the blo od cells on this slide to those on the human blood slide.
Complete Part B of the Lab Report.

Part C - Elodea & Plasmolysis

Plasmolysis can be used to see the plasma membrane in a plant cell. Normally the cell membrane is pushed up against the rigid cell wall. When a plant cell loses water, in a process called plasmolysis, the cell membrane separates from the cell wall and can be seen.

1. Obtain a single leaf tip from the Elodea sprig.
2. Float the leaf in a drop of water on a microscope slide and cover with a cover slip.
3. Observe the leaf under low-power. You should be able to distinguish the rigid cell walls outside the cell membrane.
4. Observe the green oval structures, which are the chloroplasts, inside the cell.
5. Notice the large central vacuole present in the plant cells. Animal cells will not have this large vacuole. You may have trouble distinguishing the nucleus in plant cells, as it is often pushed to one side by the large water-storing vacuole.
6. Change the environment of the living plant cell by adding a drop of 10% NaCl to the edge of the cover slip. 7. Use the adhesive and cohesive properties of water to pull the NaCl through the specimen by touching a piece of paper towel or tissue to the opposite side of the cover slip.
Complete Part C of the Lab Report.

Part D - The Cell Cycle & Mitosis

First you will need to examine mitosis in onion (Allium) cells. Obtain a prepared slide of onion root tips. These slides usually have 3 or 4 root tips on them (see figure below). With the scanning objective lens in place locate one of these root tips. As you move to higher magnifications focus on an area just a little behind the tip of the root (see figure below). This is called the root meristem and is an area where cells are actively dividing.

Using the high-power (40x) lens identify, draw and describe each of phase of mitosis (prophase, metaphase, anaphase and telophase). Use the figure below as a reference for the stages of mitosis. If you cannot find all four phases in the root tip you are focused on you may need to move to one of the other root tips.
NOTE - any cell with an intact nucleus in which individual chromosomes cannot be made out are NOT in mitosis. Those cells are in interphase.

Complete Part D of the Lab Report.

Non-majors College Biology Lab Manual © 2021 by Marie McGovern Ph.D. is licensed under CC BY-NC 4.0