The Cell Cycle and Mitosis

This lesson covers the cell cycle and mitosis as required by the Edexcel GCSE Biology specification (1BI0), Topic 1: Key Concepts in Biology. You need to understand the stages of the cell cycle, describe what happens during mitosis, and explain why mitosis is important for growth and repair.

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Why Do Cells Divide?

Cells divide for three main reasons:

1. Growth — multicellular organisms grow by increasing their number of cells.
2. Repair — damaged or worn-out cells are replaced by new identical cells (e.g. skin cells, blood cells).
3. Asexual reproduction — some organisms reproduce by mitosis, producing genetically identical offspring (clones).

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The Cell Cycle

The cell cycle is the series of events that take place in a cell, leading to cell division and the production of two new daughter cells. It is a continuous process divided into three main stages:

1. Interphase (the longest stage)

Interphase is the period of the cell cycle before mitosis begins. The cell prepares for division. Interphase occupies approximately 90% of the total cell cycle time.

During interphase: