Grade 11 Biology
Contrasting Plant and Animal Cells
Onion tissue provides excellent cells to study under the microscope. The main cell structures are easy to see
when viewed with the microscope at medium power. For example, you will observe a large circular
nucleus in each cell, which contains the genetic material for the cell. In each nucleus, are round bodies
called nucleoli. The nucleolus is an organelle, which synthesizes small bodies called ribosomes. Ribosomes
are so small, you cannot see them with the light microscope. Also present in the onion cell, is a well
developed cell wall and a cell membrane just beneath it.
Cheek cells provide an equally good opportunity to study a common animal cell under the microscope.
Clearly obvious to all will be the great difference in the relative sizes of the two. Each cell will need to be
stained with a different chemical, iodine for plants and methyl blue for animals. Iodine is particularly good
at staining carbohydrate molecules (such as those that make up the cell wall) and methyl blue adheres to
and makes protein molecules more visible.
Purpose: To study the structure of the onion epidermal cell, with particular emphasis on the nucleus and
nucleoli. To study the structure of a cheek epithelial cell, with particular emphasis on cell shape and size.
Materials: The following materials are required; onion, microscope, glass slide, coverslip, iodine stain
(Note: iodine is toxic and will stain - handle with care) Methyl blue stain, toothpick.
1. Obtain a section of a scale leaf from an onion bulb.
2. Remove the single layer of epidermal cells from the inner (concave) side of the scale leaf.
3. Place the single layer of onion cell epithelium on a glass slide. Make sure that you do not
fold it over or wrinkle it.
4. Place a drop of iodine stain on your onion tissue.
5. Put the coverslip on the stained tissue and gently tap out any air bubbles.
6. Observe the cells under 40x . Now observe the cells under 100x with the diaphragm wide
open. Slowly reduce the light intensity by closing the diaphragm, and observe the image.
Which light intensity revealed the greatest cellular detail?_____________
7. In the space provide below, draw a group of 10 neighboring cells at 100x . In one cell,
label all the parts you see.
8. Switch to high power at 400x . Can you see a whole cell? If you can, draw one cell and
label it. If no, go back to 100x and draw one cell and label it. At minimum you should
be able to observe the cell wall, cell membrane, nucleus, cytoplasm, nuclear membrane
9. Label and title your drawing using all of the microscopic drawing rules described in the
previous class. Using a clear plastic ruler determine the diameter of the field of view at
low power. Use this information to calculate the high power field diameter and then
estimate the magnification of your drawing.
PART TWO: Cheek cell wet mount
1. To view cheek cells, gently scrape the inside lining of your cheek with a toothpick. DO
NOT GOUGE THE INSIDE OF YOUR CHEEK! (We will observe blood cells in a
2. Gently smear the toothpick onto the center of a glass slide. Some of the cheek cells
should fall onto the slide.
3. Add a drop of methylene blue stain (specific for animals) and cover with a cover slip.
4. Observe the cheek cells under both low and high power of your microscope. Draw a
diagram of one cheek cell and label its parts. Use the biological drawing rules outlined in
the previous class and determine an accurate estimate of the magnification of your
drawing. Include as many labels as you can, at minimum you should observe the cell
membrane, nucleus, nuclear membrane, nucleoplasm and cytoplasm.
1. What is the function of the nucleus?
2. Where is the nucleolus found and what does it produce?
3. Describe what ribosomes do in the cell?
4. Why do we stain specimens?
5. Why must the specimen you observe be very thin?
6. Onion cells are plants. Therefore, why were there no chloroplasts in the onion cells you
7. Centrioles might be observed in some of these cells with an electron microscope. In which cells
would these be observed and what is the function of these cell organelles?