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SBI 3C
Mr. Baxter
Preparing Wet Mount Lab
MATERIALS
Onion Slice
Microscope
Microscope slides
Water
Cover slips
Eyedropper
Iodine
Methylene Blue
Tweezers
Worksheet
PROCEDURE
Preparing the wet mount slide of onion skin
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Break an onion slice in two.
Carefully pull the slice apart.
Use tweezers to pull off a very thin piece of onion skin (the thinner, the better)
Place the skin in the center of the slide. Try to keep it from folding; get it as flat as possible.
Add a drop of water to the onion skin and cover with a cover slip.
Press the cover slip down carefully to remove any air bubbles.
Place the slide on the stage of the microscope, set it to low power, adjust the focus so the onion slice is
clear. Draw four or five cells as seen. Label the cell walls.
8. Switch to higher power and try to identify the cell membrane, nucleus, and cytoplasm.
Staining the onion cells
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Lift up the cover slip and add one or two drops of iodine to the slide.
Lower the cover slip and, if there are air bubbles tap gently till they are gone.
Examine the cells on higher power (remember to start from low power)
Iodine stains different parts of the cells so that different organelles can be seen. Draw four or five cells
as seen.
5. Label the cell wall, cell membrane, cytoplasm, and nucleus on one of the cells.
For the Cheek Cell
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Take a clean Q-tip and gently swab the inside of your cheek.
Swab the Q-tip on the centre of the slide.
Prepare a wet mount like you did with the onion.
Find the cheek cells under medium power and draw your what you see
5. Stain cells using methylene blue solution as the dye (be careful it will stain cloths and skin if it gets on
you)
6. View cells under high power and do a labelled biological drawing
DISCUSSION QUESTIONS AND TASKS
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What is the general shape of the onion cells? How does that compare to the cheek cells?
Why do you think there are so many onion cells close together?
Why is it easier to see the onion cells after they are stained?
All plant cells have cell walls. What is the function of the cell wall?
Determine the size of Field of View for each drawing (show your calculations).
For the Stained slides label the actual size of one cell (in µm) on your drawing.
Cell Biology – Preparing Wet Mount Lab
Page 1
SBI 3C
Mr. Baxter
Wet Mount Lab Assessment
Name:
Did the student do the following?
APPLICATION
Found required cells
Prepared slides correctly
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Correctly identified organelles (x2)
Correctly determined field of view
Correctly determined actual size
Correctly answered discussion questions
Application Level
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COMMUNICATION
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Drawings reflected actual cells (x2)
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Drawing labelled in proper format
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Drawing magnifications and title included
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Discussion questions were answered clearly, and with
correct grammar and spelling
Communication Level
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Additional comments:
Cell Biology – Preparing Wet Mount Lab
Page 2
SBI 3C
Mr. Baxter
The Onion Cell: Observations
Cell Biology – Preparing Wet Mount Lab
Page 3
SBI 3C
Mr. Baxter
The Cheek Cell: Observations
Cell Biology – Preparing Wet Mount Lab
Page 4