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Preparing an onion cell slide
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Aim of this practical
To be able to prepare a slide of an onion cell
to be viewed under a microscope.
To accurately draw observations
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What you will need…
• Glass microscope slides
• Plastic cover slips
• Paper towels or tissue
• Iodine solution
• Plastic pipette or dropper
• Onion
• Tweezers
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1. Carefully peel back a layer of onion with
the tweezers – thinner the better.
2. Place the onion on the slide as flat as
possible.
3. Put two drops of iodine on top of the
onion (IODINE STAINS).
4. Place the coverslip over the top without
bubbles being trapped underneath.
5. Look through microscope at cells.
Method
+ Drawing Microscope Slides /
Specimens:
 Use a pencil
 Draw only the lines you see. No shading or colouring
 Each circular diagram (field of view) should be about a 3rd of
a page in size
 If the cells you are viewing are similar/repetitive it’s useful to
draw about 4-5 only
Always record the:
 magnification
 name of specimen
 and the date of the
observation
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Conclusion: What do you see?
The iodine solution stains starch in the cells
blue-black, making the cell features easier to
see.
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Preparing a cheek cell slide
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Aim of this practical
To be able to prepare a slide of a cheek cell
to be viewed under a microscope.
To accurately draw observations
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What you will need…
• Glass microscope slides
• Plastic cover slips
• Paper towels or tissue
• Methylene Blue solution
• Plastic pipette or dropper
• Cotton swabs
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Method
1. Take a clean cotton swab and gently scrape the inside
of your mouth.
2. Smear the cotton swab on the centre of the
microscope slide for 2 to 3 seconds.
3. Add a drop of methylene blue solution and place a
coverslip on top.
4. Remove any excess solution by allowing a paper
towel to touch one side of the coverslip.
5. Place the slide on the microscope, with 4x or 10x
objective in position and find a cell. Then view at
higher magnification
+ Drawing Microscope Slides /
Specimens:
 Use a pencil
 Draw only the lines you see. No shading or colouring
 Each circular diagram (field of view) should be about a 3rd of
a page in size
 If the cells you are viewing are similar/repetitive it’s useful to
draw about 4-5 only
Always record the:
 magnification
 name of specimen
 and the date of the
observation
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Conclusion: What do you see?
Methylene blue stains negatively charged
molecules in the cell, including DNA and RNA.
The cells seen are squamous epithelial cells
from the outer epithelial layer of the mouth.
The small blue dots are bacteria from our
teeth and mouth.