Biology
Cells: Living Machines
Problem: What is the basic structure of plant and animal cells?
Background: Earlier in the year, we discussed the characteristics of life. One of
those characteristics was that all living things were made of cells.
In this lab, you will be looking at two types of cells from multicellular organisms.
Using a microscope, you will examine cells from the epidermis of an onion bulb.
You will also observe epithelial cells from the inside of your mouth.
Materials (per group)
Onion
Dropper
Microscope slides and cover slips
Algae
Microscope
Stains
Cheek cells
Procedure (Part A)
1. Pull of a piece of the onion off the bulb. Bend the piece until it cracks and
you are able to peel off a piece of the thin epidermal tissue layer of the
outer skin.
2. Put a drop of water on a clean slide. Place a piece of the epidermal tissue
in the water. Use the probe to flatten the tissue onto the slide.
3. Place one drop of the stain on the onion tissue. Wait a few seconds, and
then put on a cover slip.
4. Remove excess stain from the slide and replace it with clear water. To do
this, place a small piece of paper towel next to one edge of the cover slip.
Place a drop of water at the opposite edge. The stained water will be
Biology
absorbed by the paper towel and the clear water will be drawn under the
cover slip.
5. Observe the slide on the microscope. Draw the onion tissue as it
appears under low power and high power on your lab sheet.
Estimate the size of one of the cells.
6. When done with drawing, wash your slide and cover slip. Obtain a piece
of algae. Prepare a wet mount of this, using only water – no stain.
7. Place the slide on the stage of a microscope. Focus on the upper layer of
cells on low power.
8. Draw the algae as it appears under low power and high power on
your lab sheet. Estimate the size of one of these cells.
9. After making your drawings, wash the slide and cover slip thoroughly.
Part B
1.
Wash your hands and use your finger to gently rub inside your cheek.
Make a fingerprint on a clean microscope slide. Place a drop of stain on
top of your cheek fingerprint. Add a cover slip. Warning: only
the person who has made the slide should touch it.
2. Focus on low power and locate a single cheek cell that has not been
folded.
3. Draw your check cells as they appear under low power and high
power. Estimate the size of these cells.
4. Throw the slide and coverslip away.
Biology
Analysis and Conclusions
Title the next blank page of your notebook “CELL LAB.” Write the
questions and their answers on the next blank page of your notebook.
1. Describe the shape of the onion cells, Elodea Cells, and cheek cells.
Are they regular or irregular in shape? Identify factors that might
determine cell shape and size.
2. Compare and contrast the onion cell, Elodea cell, and cheek cell. Can
you explain any differences other than the difference in shape?
3. Why was it necessary to stain the onion cell and the cheek cell?
Your teacher will ask you to share your drawings with the class and
participate in the discussion. You will use the rest of the page to write
and answer the after discussion summary questions that follow.
After Discussion Questions
1. Compare the border of the plant cells (Elodea and onion) to the border of
the animal cell (cheek cell). What types of differences can you note?
2. What internal structure(s) do human cheek cells have in common with
onion cells?
3. What is the general term for these internal structures of a cell?
4. What do these internal structures do for the cell?
5. What are some things found in the plant cells that were not found in the
cheek cells?
6. Plants are stiff and rigid. How does their cellular structure contribute to
this characteristic?
7. In summary, give at least three differences in the structures of plant and
animal cells.