Homework 5.1

Cambridge International AS and A Level Biology © Cambridge University Press 2014 1

The mitotic cell cycle

Answering these questions will help you to understand the structure of a chromosome and to apply your knowledge of the cell cycle in the interpretation of data.

1 a Describe the structure of a chromosome. [5]

b Explain the importance of telomeres. [4]

c The mitotic index can be used to quantify the proportion of cells which are undergoing mitosis. Mitotic index is calculated by dividing the number of cells observed in mitosis in the field of view by the total number of cells in the field of view.

In an investigation, the mitotic index was calculated for cells in a root, at different distances from the tip.

The results are shown below.

Distance from root tip / mm / Mitotic index
0.5 / 0.12
1.0 / 0.08
1.5 / 0.04
2.0 / 0.02
2.5 / 0.01
3.0 / 0.01

i Plot a graph to show the relationship between mitotic index and the distance from the root tip. [4]

ii Using these results, describe the relationship between the distance from the root tip and the mitotic index. Suggest an explanation for the change in mitotic index. [3]

[Total: 16]

Cambridge International AS and A Level Biology Teacher’s Resource 1