Unit 11- Genetics and Genetic Engineering
Learning Aim B: Explore how the process of cell division in eukaryotic cells contributes to
genetic variation
B.P2: Prepare microscopic slides to observe and draw the stages of mitosis and
meiosis.
B.P3: Explain the structure and function of human chromosomes.
B.M2 Demonstrate skilful preparation of microscopic slides to observe and draw
the stages of mitosis and meiosis.
B.M3 Discuss the behaviour of the chromosomes during the cell cycle stages of
mitosis and meiosis.
B.D2 Evaluate how the behaviour of the chromosomes lead to variation.
B.P2: Prepare microscopic slides to observe and draw the stages of mitosis and
meiosis.
Study of mitosis in an onion root cell:
Mitosis refers to a type of cell division (cell cycle) where the cell produces two identical daughter
cells. Unlike meiosis, which is also a type of cell division, mitosis produces two diploid daughter cells.
Both daughter cells contain the same number of chromosomes as the parent cell.
Why is an onion root used to demonstrate mitosis?
An onion root is used because it is a rapidly growing part of the
onion which is similar to the various stages involved in mitosis.
Aim of this experiment:
To study the process of mitosis by using onion root cells.
Hypothesis of this experiment: Master, M. (2022) Onion root tip mitosis - stages,
experiment and results, MicroscopeMaster. Available at:
For the purpose of maturing, growth, maintaining tissues and https://www.microscopemaster.com/onion-root-tip-
synthesising new cells; cell division is a required process. mitosis.html (Accessed: November 2022).
Recommendation:
It is important that the root tips are growing and are fresh as dried
and old root tips may lead to poor results
Equipment needed:
Microscope, Bulbs, Acetocarmine stain, Water, Burner Admin, B.J.U.S. (2021) Study of mitosis in onion root tip
N/10 Hydrochloric acid, Filter paper, Coverslip, Aceto cells - cell division process, BYJUS. BYJU'S. Available at:
https://byjus.com/biology/study-of-mitosis-in-onion-root-
alcohol (Glacial acetic acid and Ethanol in the ratio 1:3),
tip-cells/ (Accessed: October 18, 2022).
Glass Slide, Onion root peel, Forceps, Blade, Watch glass,
Dropper, Needle and a Vial.
Method:
, Place an onion on a tile.
Use a sharp blade and carefully cut the dry roots of the onion.
Then, use the bulbs in a beaker containing water to the tips of the root.
The new roots will take up to 4 to 6 days to grow and appear.
Next, cut approximately 3cm of the new roots and put them in the watch glass.
With the help of a forceps, move it in the vial containing the aceto-alcohol (the mixture
containing glacial acetic acid and ethanol in the ratio 1:3).
Leave the roots in the vial for one complete day.
Using the forceps again, pick one of the roots and transfer it to a glass slide.
Then, using a dropper put one drop of N/10 hydrochloric acid on the tip of the onion root
cell and add 2 to 3 drops of acetocarmine stain.
Carefully, heat the stain on the burner so the stain does not dry up.
The excess stain can easily be removed using the filter paper.
Trim the more stained part using a blade
Discard the less stained part whilst keeping the more stained part.
Add a drop of water to it using the dropper.
Using the needle, place a coverslip on your slide.
Tap the coverslip gently using the unsharpened end of the needle so that the tissue of the
onion root is visible under the coverslip and straightening it out as a fine layer of the cell.
The onion root cells are now ready to be examined under a microscope.
Finally, observe these cells by placing them under a microscope and use the focus knobs as
desired for a clear magnification.
Risk assessment:
Wear eye protection.
Be extremely careful when handling the sharp objects such as the blade and needle.
Wear gloves to avoid burns and stains because of the corrosive solutions.
Be aware that aceto-alcohol is extremely corrosive. It might cause burns, inflammation and
stains. To avoid contact with the eyes and skin make sure to wear gloves and eye protection.
If the contact does happen, make sure to wash the affected areas thoroughly with water.
Clean all the spillages immediately.
Keep the glassware items such as coverslips well away from the edge of the desk to avoid
the risk of getting cuts from sharp objects.
Handle the burner with great care or seek supervision to avoid burning yourself.
If you are a child, seek adult supervision because of sharp objects, corrosive solutions and
burners.
Conclusion/Results:
By performing this experiment, you will notice that the onion has 8 pairs of chromosomes because
less chromosomes are easier to observe when they condense. Additionally, the onion root cells will
divide rapidly because the roots absorb water and various
minerals from the soil. Because of this, we can identify different
stages of mitosis based on the distribution of the chromosomes.
B.P3: Explain the structure and function of human
chromosomes.
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