IGCSE Biology / Cell division
Mitosis and growth revision notes
Edexcel International GCSE Biology (4BI1), chapter 17: Cell division, specification point 3.28, 3.29. Free lesson.
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Mitosis is cell division that produces two genetically identical daughter cells, each with the full chromosome number. It is used for growth, repair, replacement and asexual reproduction.
What happens during mitosis
The stages are easiest to remember by following the chromosomes. DNA is copied before division begins, so each chromosome consists of two identical strands joined together.
Why the daughter cells are identical
Each new cell receives one of the two identical strands from every copied chromosome. Because the DNA was copied exactly, both daughter cells have the same genetic information and the full chromosome number. Mitosis keeps the chromosome number constant. If DNA were not copied first, division would leave each cell with only half the chromosomes.
Where mitosis happens and what it is used for
Mitosis is useful wherever an organism needs more cells or identical replacements. In plants, it is concentrated in meristems, regions at the root and shoot tips where growth occurs. Growth: repeated mitosis allows a fertilised egg to develop into a whole organism, with the same genetic information in every cell. Repair: damaged tissue is replaced by the same kind of cells, such as when a wound heals. Replacement: mitosis continually produces new cells to replace ones that wear out. Red blood cells last about 120 days, while skin cells last far less. Asexual reproduction:…
How to describe mitosis accurately
A description that says chromosomes line up and are pulled apart, making cells with half the chromosomes, misses the DNA-copying step. Mitosis produces cells with the full chromosome number; division that halves the number describes meiosis, not mitosis. State that DNA is copied before division. Explain that one identical strand from each chromosome goes to each new cell.