Download Lab #5 - Onion Cells (Oct. 21 2014)

Name: ________________________ Date:_________________
Lab Partners: ____________________________________________
Purpose: Students will make and stain a wet mount slide of onion cells and observe the cell walls, nucleus,
cytoplasm, and cell membrane.
Materials:
microscope
cover slips
glass slides
medicine dropper
lens paper
tweezers
Iodine solution
rubber gloves
Procedure 1: Wet Mount of an onion skin
1. Clean the slide and cover slip with the lens paper.
2. Break an onion slice in two. Carefully pull the slice apart.
3. Use tweezers to pull off a very thin piece of onion skin.
4. Place the skin in the center of the slide. (Keep it from folding.) Flatten it as much as possible. Avoid
wrinkling the epidermis. If wrinkles develop, use the tweezers to gently un-wrinkle the tissue without
tearing it.
5. Add a drop of water to the onion skin and cover with a cover slip.
6. Press the cover slip down carefully to remove any air bubbles.
7. Place the slide on the microscope stage. Set lens to low power, adjust the focus so the onion slice is
clear.
8. Switch to high power and draw what you see the small circle below. Include a title,
magnification and try to label the cell walls, nucleus, and cytoplasm.
Title: ____________________________________
Magnification:________________
Procedure 2: Staining of an onion skin
1. Complete procedures 1 -4 from above
2. Add a drop of water to the onion skin and one to two drops of Iodine solution to the slide.
3. Leave the slide for 2-5 minutes to allow the stain to enter the cell.
4. Lower the cover slip and examine the cell on high power.
5. With the iodine solution you should be able to see structures of the cell you could not see
before. Draw one cell on the back of your sheet in the space provided. Label your drawing of the
cell structures (cell wall, cell membrane, nucleus, and cytoplasm) and include a title, scale and the
magnification.
6. Please answer the Post Lab Questions write about the lab and what you learned.
Name: ________________________ Date:_________________
Post Lab #5 Assignment Questions:
1. Describe the shape of a single cell of an onion epidermis.
2. Describe the arrangement of the cells with respect to one another. Describe what they look like.
3. Describe the nucleus of a cell. What is it’s function
4. Describe how the iodine stain that you used helped you see the cellular detail. What parts of the cell
were you able to see better?
5. If 10 cells fit across the field of view, estimate the length of a single cell in micrometres (μm or 10-6
meters) assuming that the field of view under high power is approximately 500 μm across. Explain your
answer.
6. In your diagrams on the previous page label all the parts of a cell that you can see such as the cell wall,
nucleus, cytoplasm, cell membrane, nuclear membrane, nucleolus, vacuole, oil droplets. Make sure you
follow proper labeling rules. What are 3 rules when making scientific drawings?
7. Describe the functions of each cell of the parts you labeled.
8. What are the 3 main differences between plant and animal cells?
(please note that flagellum is NOT one of the differences.