Using a Microscope to See Different Types of Cells

All organisms are made up of cells - a cell is the simplest collection of matter that can live. Most cells are very small, so we need to use a microscope to see them.

Cells can live alone, doing everything they need, or they can live together with other cells by forming multi-celled organisms like humans, other animals, and plants. Our bodies consist of more than a billion cells, with each type of cell having its own special function. All the different cells communicate and cooperate with each other to accomplish all the functions that our bodies need. In contrast, there are organisms called Protists that are single-celled organisms and do all the different functions that are needed to live.

In this lab, we will be using a microscope to look at different types of cells. A microscope (micro = tiny or small; scope = to see) is really just two magnifiers or lenses working together. The objective lens (near the object) is down near the slide and the other is inside the cylinder that you look into (it is called the eyepiece, being near your eye). Together, these lenses are able to magnify an object much more than a single lens can.

Cells in Humans (cheek cells and bacteria in the mouth)

Procedure for cheek cells in your mouth

1. Hold a toothpick flat against your inner cheek and scrape the inside of your cheek. This will release some of the cells lining your cheek.

2. Spread the cells on a clean slide by rubbing the toothpick flat against the slide. Make sure you get plenty on the slide so you can easily find them under the microscope - you want to be able to see a kind of smear on the slide with just your eyes.

3. Add no more than one or two drops of methylene blue stain on the cells. Count to ten and then carefully place the cover slip over the area starting at an angle to avoid bubbles. Always put the slide on the microscope stage using the lowest power of the objective lens. Look around and when you see something, go to a higher power as needed to find the actual cells.

The methylene blue stain allows you to see the cells clearly. Look carefully for some pale irregular shapes with a blue circle or oval in the middle. Most cheek cells will show this; the oval is the nucleus of the cell, where the DNA is located. The DNA contains all the instructions for the cell's activities through its life.

4. Look at your slide under the microscope and sketch what you see in the space below.

Are any of your cells in groups?

Procedure for bacteria in your mouth

1. Stick a fresh toothpick between your teeth and wiggle it. To be sure you have a lot of bacteria, repeat 2 or 3 times using different teeth in your mouth.

2. Smear the end of the toothpick on the new slide and cover an area about the size of a cover slip.

3. Add no more than 1-2 drops of methylene blue to the slide on top of your smear.

4. Wait 20-30 seconds and then put a cover slip over the methylene blue drop, starting at an angle to avoid bubbles.

5. Remove any extra stain from the edge of the cover slip with a paper towel.

6. Look at the slide you have prepared under the microscope using medium power and sketch what you see.

7. Bacteria appear as very, very small blue-stained rods or spheres, which look like circles. These are the two different main groups of bacteria. See if you or other members of your group can find both kinds of bacteria. Sometimes the rods are in long chains like tiny necklaces because they grow lengthwise and often stay connected after dividing. You may also see smeary stuff, which is probably your saliva or partially digested food from your teeth.

8. Go back and look at your cheek cell slide again. Can you find any bacteria on top of the cheek cells? The human mouth is full of bacteria, and although most bacteria in the mouth are found on or between the teeth, sometimes there are bacteria living right on the cells.

9. What is (roughly) the difference in size between the bacteria and the cheek cell? This is easy to see if you find a bacterium on top of a cheek cell.

10. Can you see a nucleus in the bacteria?

Procedure for Sperm Cells

Look at a prepared slide of human sperm.

Draw a few sperm.

Protists (Paramecia & Amoebas)

Procedure for Paramecia

Protists are usually very motile, because they have to move around to find food. We will be using a prepared slide to look at Paramecia.

Sketch a Paramecium.

Since it is an animal and must eat, can you see a mouth?

Procedure for Amoebas: (often called Amoebae)

Sketch an amoeba.

Since it is an animal and must eat, can you see a mouth?

Comparisons

1. How do you think the cheek cells and sperm cells get food as compared to the Paramecia and Amoebas?

2. Could cheek cells or sperm cells survive as a single-celled organism? Why or why not?