Roles of mitosis and meiosis at Higher Level: The same statement as SL. At HL a four-mark 'distinguish between mitosis and meiosis' is a favourite Paper 2 opener.
Practise this as you read
- State why the nucleus divides before the cell.
- Distinguish between mitosis and meiosis.
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The big idea: In eukaryotes the nucleus divides before the cell does, so that no daughter cell is left anucleate (without a nucleus).
The points to remember
- The nucleus holds the cell's genes, which control the cell's activities.
- An anucleate cell cannot make new proteins for long and can never divide.
- So nuclear division (mitosis or meiosis) comes first.
- Then cytokinesis splits the cytoplasm between the new nuclei.
Remember it as: Divide the nucleus, then the cell.
Real example: phloem sieve tubes. The sieve tube cells of phloem lose their nucleus as they mature and can never divide again. A companion cell beside each one keeps its nucleus and supports it.
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Two kinds of nuclear division: Mitosis keeps the chromosome number and the genome the same. Meiosis halves the chromosome number and makes every cell genetically different.
| Mitosis | Meiosis | |
|---|---|---|
| Chromosome number | Kept the same | Halved |
| Genome of daughter cells | Identical to the parent | Different: genetic diversity |
| Daughter cells | Two | Four |
| Roles | Growth, repair, replacement, asexual reproduction | Making gametes for sexual reproduction |
Why halve the number?: At fertilisation two gametes fuse. If they were not haploid, the chromosome number would double in every generation.
How it is asked: A Paper 2 'distinguish between mitosis and meiosis', a 1B 'distinguish between the cells produced', or a 1A item on what each division does to the chromosome number.
IB-style questionDistinguish[4 marks]
Distinguish between cell division by mitosis and by meiosis in eukaryotes.
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