Observe the mitosis in cells

Observe the mitosis in cells

How to prepare a root of onion


a Cut off 1-2 cm of the root tips. Put in a small volume of ethanoic acid and carmin on a test tube.

b Meanwhile, heat 10-25 cm3 of acetic carmin to 90 °C.

c Wash the root tips in cold water for 1 minute.

d Cut each about 2 mm from the growing root tip. Discard the rest, but keep the tips

e Cover with a water drop and the coverslip and then squash

f Place the slide and coverslip on a double layer of paper towel and fold the paper over the coverslip. Make certain that the slide is on a flat surface and squash down on the coverslip with a strong vertical pressure, using your thumb. Do not twist or roll the thumb from side to side


g View the root tips under a microscope (x400 magnification) and look for the chromosomes within cells which are actively dividing.

h Locate the meristematic zone, which has small, apparently ‘square’ cells with nuclei which are large relative to the whole cell area.

D’après svt ac.Lyon

m If cells are overlapping, squash the slide again. Avoid moving the coverslip from side to side.

n Make sketches of (or take photographs of) cells that show any of the stages of mitosis.

o If we have time we can calculate the mitotic index :

Mitotic index = number of actively dividing cells in field of view/ Total of cells in field of view

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