Mitosis in onion root tip 12th class biology experiment

Procedure
Growing of root tips
Select a few medium-sized onion bulbs. Carefully remove the dry roots
present. Grow root tips by placing the bulbs on glass tubes (of about 3–4
cm. diameter) filled with water. Care should be taken so that the stem portion
of the bulb (basal part) just touches the water. A few drops of water may be
added periodically to compensate evaporation losses. New roots may take
3–6 days to grow. Cut 2–3 cm long freshly grown roots and transfer them to
freshly prepared fixative, i.e., aceto-alcohol (1:3:: glacial acetic acid : ethanol).
Keep the root tips in the fixative for 24 hours and then transfer them to 70%
ethanol (for preservation and use in future). Onion root-tip cells have a cell
cycle of approximately 24-hour duration, i.e., they divide once in 24 hours,
and this division usually takes place about two hours after sunrise. Therefore,
roots grown on water should be cut only at that time to score maximum
number of dividing cells.
Preparation of slide
Take one or two preserved roots, wash them in water on a clean and grease￾free slide. Place one drop of N/10 HCl on the root tip followed by 2–3 drops
of aceto-carmine or aceto-orcein stain on it. Leave the slide for 5–10 minutes
on a hot plate (or warm it slightly on spirit lamp). Care should be taken that
the stain is not dried up. Carefully blot the excess stain using blotting paper.
Now cut the comparatively more stained (2–3 mm) tip portion of the root
and retain it on the slide and discard the remaining portion. After
(10–20 seconds) put one or two drops of water and blot them carefully using
blotting paper. Again put a drop of water on the root tip and mount a cover
slip on it avoiding air bubbles. Place the slide in between the folds of blotting
paper using the fingers in such a way that the cover slip mounted on the
slide is properly held. Now slowly tap the cover slip using the blunt end of a
pencil so that the meristematic tissue of the root tip below the cover slip is
properly squashed and spread as a thin layer of cells. Carefully seal the
margins of the cover slip using molten paraffin wax or nail polish. This
preparation of onion root tips cells is now ready for the study of mitosis.

Study of slide
Place the slide on the stage of a good quality compound microscope. First
observe it under the lower magnification (10 X objective) to search for the
area having a few dividing cells. Examine the dividing cells under higher
magnification of the microscope to observe the detailed features of mitosis.

Questions
1. Suggest names of a few tissues, which are suitable for the study of mitosis.
2. Why is mitosis also known as equational division?
3. What shape would a metacentric and a sub-metacentric chromosome exhibit
during the anaphase stage?
4. How does cytokynesis differ in plant and animal cells?

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