Download biology i: cell structure lab

BIOLOGY I: CELL STRUCTURE LAB
A. INTRODUCTION
The cell is the basic unit of life. To understand how a cell functions it is important to have an idea of their structure. In this
lab you will examine three different cells: onion epidermis, elodea, and human cheek. These cells are representative of
eukaryotic cells in general and will help us compare and contrast animal and plant cells. Your data will include the answers
to the numbered questions in the lab directions and your drawings of these cells. When sketching a magnified specimen
your drawing should indicate what you are drawing, what power your drawing reflects, and label any organelles you can
identify.
B. MATERIALS
Microscope & slide
Dropper
Elodea
Cover slip
Toothpick
Onion
20% salt solution
Iodine stain
Forceps
C. PROCEDURE
Onion Epidermis
1.
2.
 Separate a piece of onion from the bulb. Hold it in your fingers and snap it in half. Peel away a piece of
the thin transparent covering from the inside of the curved section.
 Mount this thin layer of tissue, being careful to keep it just one layer on the slide, add a drop or two of
iodine and a cover slip.
 Examine it under low power first and then move to medium and high power.
 Draw 2-3 cells as they appears under high power. Label any structures you can actually see. If you
can’t tell what something is, make an educated guess.
Briefly describe a single cell.
What feature(s) of these cells make them look like plant cells?
Elodea
 Elodea is an aquatic plant with very thin leaves. It is possible to mount a whole leaf and examine living
cells.
 Pull the leaf from the tip of the Elodea sprig and mount it with a drop of water and a cover slip.
 Examine it under low, medium and high power.
 Draw 2-3 cells as they appears under high power. Label any structures you can actually see. If you
can’t tell what something is, make an educated guess.
3. Why don’t the Elodea cells need stain for you to get a good view of them?
4. Did you observe the chloroplasts moving in lazy circles around the cell? This is a process called “cyclosis” or
cytoplasmic streaming and is still not completely understood.
5. Do you think the Elodea cells have the same function as the onion cells? Why or why not?
 Because the cell membrane in a plant cell is pressed tightly against the cell wall, it is difficult to see. If
however, a plant cell is placed in a strong salt solution, water will leave the cell. This loss of water
shrinks the volume and the cell membrane pulls away from the wall and is visible.
 Add salt solution to your Elodea cell and wait 2 minutes.
 Draw 2-3 cells under high power now.
Cheek Cells
6.
7.
 Epithelial cells line surfaces inside and outside our body. These cells are specialized for transport and/or
protection forming barriers. Gently, with the rounded end of a toothpick, scrape the inside of your cheek.
 Rub these cells on the surface of a slide, add a drop of iodine and cover clip.
 View under low, medium and high power in that order.
 Draw 2-3 cells as they appears under high power. Label any structures you can actually see. If you
can’t tell what something is, make an educated guess.
How does the shape of these cells compare with the plant cells?
Compare and contrast the animal and plant cells you examined today. Refer to your cell diagrams too.