CB2.1 — Mitosis and the cell cycle (Edexcel 1SC0)
Mitosis is cell division for growth and repair — producing two genetically identical daughter cells from one parent cell.
The cell cycle
- Interphase (longest stage): DNA replication; cell grows; organelles duplicate.
- Mitosis: nucleus divides into two identical nuclei.
- Cytokinesis: cytoplasm divides; two daughter cells formed.
Stages of mitosis (PMAT)
- Prophase: chromosomes condense and become visible; nuclear envelope breaks down.
- Metaphase: chromosomes line up at the cell equator.
- Anaphase: chromatids pulled to opposite poles by spindle fibres.
- Telophase: nuclear envelopes reform around each set of chromosomes.
Key facts
- Human body cells contain 46 chromosomes (23 pairs).
- Each chromosome is replicated in interphase → two chromatids joined at centromere.
- Daughter cells are genetically identical to each other and to the parent cell.
- Mitosis occurs in all body cells for growth, repair and asexual reproduction.
Cancer
Cancer is uncontrolled cell division — mitosis continues without the normal regulatory signals. Causes include: mutations in DNA (from UV light, ionising radiation, certain chemicals), viral infections.
- Tumour: mass of rapidly dividing cells.
- Benign tumour: does not invade surrounding tissue.
- Malignant tumour: invades and spreads to other parts of the body (metastasis).
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