Mitosis in a root tip Use either Allium cepa (onion) or Vicia faba (broad bean).

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 • Place root-tips of about 0.5 – 1 cm length in 5M HCl and leave for 5 minutes. • Wash with distilled water. • Place on a microscope slide with a few drops of lactoproprionic orcein stain. • 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). • 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). • 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. • 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).