The Cell Cycle and Mitosis

Cell division is essential for growth, repair and replacement of cells in multicellular organisms. The Edexcel A-Level Biology specification (9BI0) requires a detailed understanding of the cell cycle, including interphase and the stages of mitosis, as well as the role of mitosis in organisms and how the cell cycle is controlled.

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The Cell Cycle

The cell cycle is the ordered sequence of events that takes place from the formation of a cell to the point at which it divides into two new daughter cells. In actively dividing human cells, the cell cycle typically lasts around 24 hours, though this varies significantly depending on cell type.

The cell cycle consists of three main phases:

1. Interphase (approximately 90% of the cell cycle)
2. Mitosis (nuclear division)
3. Cytokinesis (division of the cytoplasm)

The following diagram shows the stages of the cell cycle as a continuous loop:

graph LR
    A["G1<br/>Cell growth"] --> B["S Phase<br/>DNA replication"]
    B --> C["G2<br/>Preparation"]
    C --> D["Mitosis<br/>Nuclear division"]
    D --> E["Cytokinesis<br/>Cell division"]
    E --> A

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Interphase