Cell Division by Mitosis

This lesson covers the cell cycle and mitosis as required by AQA GCSE Biology specification 4.1.1. You need to understand why cells divide, the stages of the cell cycle, and what happens during mitosis. You also need to know about the role of mitosis in growth, repair, and asexual reproduction.

---

Why Do Cells Divide?

Cells need to divide for three main reasons:

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

---

The Cell Cycle

The cell cycle is the series of stages a cell goes through as it grows and divides. It consists of three main phases:

1. Interphase (Growth Phase)

This is the longest phase of the cell cycle — the cell spends most of its life in interphase. During interphase, the cell: