Form 4 · Common mistakes

Cell Division, common mistakes

The mistakes SPM students make on Cell Division, why each one loses marks, and the correct version.

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The mistakes, why they lose marks, and the fix

Common mistake	Why it loses marks	What earns the mark
Saying mitosis produces gametes.	Gametes are produced by meiosis; mitosis produces body cells for growth and repair.	State that meiosis produces gametes, while mitosis produces identical diploid body cells.
Writing that meiosis produces two cells.	Meiosis has two successive divisions, so it produces four cells, not two.	State that meiosis produces four haploid cells, while mitosis produces two diploid cells.
Confusing diploid and haploid.	Diploid (2n) cells have chromosomes in pairs; haploid (n) gametes have one of each pair.	State that a body cell is diploid with paired chromosomes and a gamete is haploid with single chromosomes.
Getting the order of the mitosis stages wrong.	The stages always run prophase, metaphase, anaphase, telophase.	Keep the order PMAT: prophase, metaphase, anaphase, telophase.
Saying meiosis happens in every cell of the body.	Meiosis occurs only in the reproductive organs, such as the testes and ovaries.	State that ordinary body cells divide only by mitosis; meiosis is limited to reproductive organs.
Treating a tumour and cancer as the same thing.	Only a malignant tumour that invades and spreads is classified as cancer; a benign tumour does not spread.	State that a tumour becomes cancer only when it is malignant and able to invade and spread.
Thinking the chromosome number doubles after mitosis.	Mitosis keeps the diploid number constant; the number neither doubles nor halves.	State that the daughter cells of mitosis have the same diploid number as the parent cell.
Saying DNA is replicated during mitosis.	DNA is replicated during interphase, before the mitotic phase begins.	State that DNA replication happens in interphase, so chromosomes enter mitosis already doubled.
Using 'chromosome' and 'chromatid' as if they are the same.	After replication, one chromosome consists of two identical sister chromatids joined at a centromere.	State that a replicated chromosome is made of two sister chromatids until they separate in anaphase.
Saying homologous pairs separate during mitosis.	Mitosis separates sister chromatids; homologous pairs separate only in meiosis I.	State that sister chromatids separate in mitosis, while homologous pairs separate in meiosis I.
Thinking the chromosome number is halved during meiosis II.	The number is halved in meiosis I when homologous pairs separate; meiosis II separates sister chromatids.	State that the reduction to haploid happens in meiosis I, not meiosis II.
Assuming cytokinesis is the same in plant and animal cells.	An animal cell forms a cleavage furrow, while a plant cell forms a cell plate because of its cell wall.	State that animal cells pinch in with a cleavage furrow and plant cells build a cell plate.

How to avoid these mistakes

Build a detailed comparison table of mitosis and meiosis, covering the number of daughter cells produced, their ploidy, and the biological purpose each division serves.
Learn the four stages of mitosis in order, prophase, metaphase, anaphase, telophase, and draw a simple, clearly labelled sketch of the chromosomes at each stage.
Explain, in full sentences rather than one word, why halving the chromosome number in the gametes keeps the species' chromosome number constant across every generation.
Sketch the four stages of mitosis in order, labelling what happens to the chromosomes in each one.
Write out, step by step, how meiosis reduces the chromosome number from diploid to haploid across its two divisions.
Explain in your own words why a malignant tumour is dangerous, using the idea of uncontrolled cell division.

Frequently asked questions

What is the difference between mitosis and meiosis?

Mitosis produces two genetically identical diploid cells and is used for growth and repair. Meiosis produces four genetically different haploid cells (gametes) and halves the chromosome number, which keeps the species number constant at fertilisation and adds variation. Both processes begin from the same parent cell, but they are used for entirely different biological purposes.

Why must gametes be haploid?

If gametes were diploid, fertilisation would double the chromosome number every generation. Because meiosis makes haploid gametes, the diploid number is restored, not doubled, when the sperm and egg fuse, keeping it constant across generations. This restoration of the diploid number at fertilisation is the whole reason meiosis exists.

How is cancer related to cell division?

Cancer arises when the normal controls on the cell cycle fail and cells divide continuously without stopping. This uncontrolled mitosis forms a tumour, and a malignant tumour can spread to other tissues. Not every tumour is cancerous, only a malignant one that invades and spreads is classified as cancer.