A level Biology B · Edexcel 9BI0 · Topic 2D
The cell cycle and mitosis
Key points
- Interphase (G1, S, G2) is the longest stage: the cell grows, makes organelles and replicates its DNA in the S phase.
- Mitosis: prophase (chromosomes condense, nuclear envelope breaks down), metaphase (chromosomes line up at the equator on spindle fibres), anaphase (centromeres split, chromatids pulled to opposite poles), telophase (nuclear envelopes reform), then cytokinesis.
- Mitosis makes two genetically identical diploid cells for growth, repair and asexual reproduction.
- Mitotic index = number of cells in mitosis ÷ total number of cells counted.
- In the root tip practical, tissue is treated with acid to separate cells, stained and squashed into a single layer.
- Uncontrolled mitosis can lead to cancer.
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Multicellular organisms grow, repair damage and sometimes reproduce asexually by making new cells that are genetically identical to the parent. The cell cycle is the ordered sequence of events that makes this possible.
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