Ijmb Model Questions Vol1 2017 Biology Question 2

A student investigates the effect of colchicine on mitosis in the root tip cells of Allium cepa (onion). Three sets of root tips are prepared: 1. Control (no colchicine) 2. 0.1 % colchicine solution for 4 h 3. 0.5 % colchicine solution for 4 h For each set, 200 cells are examined under a microscope and the numbers of cells observed in the four stages of mitosis are recorded as shown in the table. | Treatment | Prophase | Metaphase | Anaphase | Telophase | |-----------|----------|-----------|----------|-----------| | Control | 30 | 20 | 15 | 10 | | 0.1 % | 20 | 35 | 10 | 5 | | 0.5 % | 10 | 45 | 5 | 5 | Tasks: a) Calculate the mitotic index for each treatment. (Mitotic index = (total number of cells in all mitotic stages / total cells examined) × 100%). b) Identify which treatment shows the highest mitotic index. c) Explain the observed effect of colchicine on the distribution of cells among the mitotic stages. d) Suggest one precaution that should be observed when preparing the colchicine solutions to avoid experimental artefacts.