Scientists studying cell division in root tip meristems calculate the mitotic index to estimate the rate of growth.
The formula for the mitotic index is:
mitotic index=number of cells showing mitosistotal number of cells×100 \text{mitotic index} = \frac{\text{number of cells showing mitosis}}{\text{total number of cells}} \times 100 mitotic index=total number of cellsnumber of cells showing mitosis×100A student examines a prepared slide of an onion root tip and counts 12 cells undergoing mitosis and 138 cells in interphase (not undergoing mitosis). Calculate the mitotic index for this sample.
In another slide of a garlic root tip, the student calculates a mitotic index of 6.5%6.5\%6.5%. If the total number of cells counted in this slide was 400, calculate the number of cells that were undergoing mitosis.
Explain one difficulty a student might face when trying to accurately count the cells to calculate the mitotic index.
3 exam-style questions on Edexcel IGCSE Biology Cell structure. Each one has a worked solution and a mark scheme showing where the marks go.