Every time your body grows, heals a cut or replaces worn-out cells, it uses mitosis: a nuclear division that makes genetically identical cells. Extended: why the chromosomes are copied first, how the copies separate, and how stem cells give rise to specialised cells.
Mitosis is nuclear division giving rise to genetically identical cells. It is used for growth, repair of damaged tissues, replacement of cells and asexual reproduction. Extended: the chromosomes are replicated exactly before mitosis, and during mitosis the copies separate, so each daughter cell keeps the same chromosome number.
Fig. 1: mitosis in a cell with two pairs of chromosomes gives two genetically identical cells
Section 01
Copy, line up, separate.
The sim cell has two pairs of chromosomes: red ones came from one parent and blue ones from the other. Press Next step and watch the readout of chromosomes per cell at every step.
Mitosis is a nuclear division that gives rise to genetically identical cells. You do not need to learn the names of its stages.
Extended.Exact replication: before mitosis, each chromosome is copied exactly, so it is made of two identical strands joined in the middle.
Extended.Copies separate: during mitosis the two copies of each chromosome are pulled to opposite ends of the cell, so each daughter cell gets one copy of every chromosome. The chromosome number stays the same: 4 in the sim, 46 in a human body cell.
Examiner trap
Mitosis does not halve the chromosome number. A human body cell with 46 chromosomes gives two cells that each have 46, with exactly the same alleles.
Stage 1 · Learn
Check what the sim just showed you
Four quick checks. Each correct answer earns XP and records this skill on your profile.
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In the sim, how many chromosomes are in each cell at the end of mitosis?
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At the step Chromosomes copied, what has happened to each chromosome?
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What happens at the step Copies separate?
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Extended: after pressing Stem cell, what does one daughter cell become?
Section 02
What mitosis is for.
Mitosis makes more cells that are just like the parent cell. That is exactly what an organism needs whenever new body cells are required.
Role
Example
Growth
a zygote dividing to form an embryo; root tips and shoot tips growing
Repair of damaged tissues
new skin cells closing a cut; a broken bone healing
Replacement of cells
replacing red blood cells and the lining of the gut as they wear out
Asexual reproduction
a potato tuber or a strawberry runner producing offspring identical to the parent
Section 03
Stem cells.
Extended. Press Stem cell (Extended) in the sim above. One daughter cell stays round and unspecialised; the other stretches into a long muscle cell.
Stem cells are unspecialised cells that divide by mitosis to produce daughter cells that can become specialised for specific functions.
Keeping a supply: one daughter cell can remain a stem cell and divide again, while the other develops into a specialised cell such as a muscle cell, a red blood cell or a nerve cell.
Where: embryos contain stem cells that can become almost any cell type; adults keep some, for example in bone marrow, which makes new blood cells.
Examiner trap
Stem cells are not already specialised. They become specialised only after dividing, when a daughter cell develops a particular structure and job.
Stage 2 · Exam
Exam-style questions
Unlocks once the four checks above are done. Worth more XP, written to IGCSE Paper 2 and Paper 4 standard.
Finish the four checks above to unlock the exam questions
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Which describes mitosis?
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Which process does NOT involve mitosis?
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Extended: a human body cell has 46 chromosomes. How many chromosomes will each daughter cell have after mitosis?
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Extended: which statement about stem cells is correct?
Skill unlocked
Mitosis, mastered.
This skill is now recorded on your profile. Keep the chain going.