Mitosis%20in%20a%20root%20tip

1
Mitosis in a root tip Use either Allium cepa
(onion) or Vicia faba (broad bean). The roots of
onion/broad bean are very convenient for showing
stages of mitosis, provided they are fresh and in
a growing condition. Chromosomes of Allium 2n
16 NOTE 3 zones of growth can be detected-
division
enlargement
differentiation
The most satisfactory squashes of roots can be
made by the following technique, using
acetic-orcein stain (or propionic-orcein) METHOD

1. Place root-tips of about 0.5 1 cm length in 5M
   HCl and leave for 5 minutes.
2. Wash with distilled water.
3. Place on a microscope slide with a few drops of
   lactoproprionic orcein stain.
4. Macerate with a glass rod (or break up the root
   tip with a needle so that it is spread out thinly
   (try to keep the arrangement of the root so you
   know which cells were part of the extreme tip).
5. Put on a coverslip and using a piece of filter
   paper press down gently with your thumb (press
   down vertically and do not displace the
   coverslip).
6. View the slide under low power and look for
   stages of mitosis. Using the high power
   magnification draw cells showing at least three
   different stages.
7. Select random fields of view in areas where you
   find dividing cells. Count the number of cells in
   interphase, prophase, metaphase, anaphase and
   telophase. Use these numbers to calculate the
   percentage of time spent in each stage of the
   cell cycle.

2
Photograph of an onion root-tip squash
From AQA AS Jan 2005, Unit 2 making use of
biology
0.02 mm
Safety!
Wear eye protection when handling hydrochloric
acid!
Irritant! Hydrochloric acid (HCl).