What are the main stages of cell division in the context of Cambridge IGCSE Coordinated Science?

In the Cambridge IGCSE Coordinated Science curriculum, cell division primarily involves two processes: mitosis and meiosis. Mitosis is responsible for growth and repair, producing two identical daughter cells, while meiosis is crucial for sexual reproduction, resulting in four genetically diverse gametes.

How does mitosis differ from meiosis in terms of their roles in inheritance?

Mitosis and meiosis serve different roles in inheritance. Mitosis ensures that each new cell receives an exact copy of the parent cell's DNA, maintaining genetic consistency. In contrast, meiosis introduces genetic variation by reducing the chromosome number by half and allowing for recombination, which is essential for producing genetically diverse offspring.

Why is cell division important for organisms, as covered in the Cambridge IGCSE Coordinated Science syllabus?

Cell division is crucial for organisms because it enables growth, tissue repair, and reproduction. In multicellular organisms, mitosis allows for the replacement of damaged or dead cells, while meiosis is vital for producing gametes, ensuring genetic diversity and the continuation of species.

What are the key differences between prophase in mitosis and prophase I in meiosis?

In mitosis, prophase involves the condensation of chromatin into visible chromosomes and the breakdown of the nuclear envelope. In meiosis, prophase I is more complex, featuring homologous chromosomes pairing up and exchanging genetic material through crossing over, which increases genetic diversity.

How does the process of crossing over during meiosis contribute to genetic variation?

Crossing over occurs during prophase I of meiosis, where homologous chromosomes exchange segments of DNA. This process creates new combinations of alleles, contributing to genetic variation among offspring, which is a key concept in inheritance and evolution as taught in the Cambridge IGCSE Coordinated Science curriculum.

Why is "Stating that gametes are produced by mitosis" a common mistake in Cell Division ?

Why it happens: Students know mitosis is the common cell division and apply it to gamete production. How to avoid it: Gametes are produced by **meiosis** (to halve chromosome number). Mitosis produces somatic (body) cells for growth and repair. Source: 0654 Examiner Report 2022

Why is "Stating that meiosis produces genetically identical cells" a common mistake in Cell Division ?

Why it happens: Students confuse the two types of cell division. How to avoid it: Mitosis = identical cells. Meiosis = **genetically varied** cells (due to crossing over and independent assortment).

Why is "Stating that mutations are always harmful" a common mistake in Cell Division ?

Why it happens: The word 'mutation' has negative connotations in everyday language. How to avoid it: Most mutations are **neutral** (no effect on phenotype). Some are harmful; a small number can be beneficial (e.g. antibiotic resistance in bacteria, sickle cell trait protecting against malaria).

Why is "Stating that Down syndrome is caused by an extra chromosome 21, but attributing it to the wrong cause" a common mistake in Cell Division ?

Why it happens: Students know it involves an extra chromosome but do not explain non-disjunction. How to avoid it: Down syndrome = trisomy 21 caused by **non-disjunction** during meiosis. Always explain the mechanism: chromosome pair fails to separate → gamete with two chromosomes 21 → trisomy after fertilisation.

InheritanceCambridge IGCSE Coordinated Sciences 0654

Cell Division

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Cell Division — Cambridge IGCSE Coordinated Science 0654

Mitosis produces identical diploid cells for growth and repair. Meiosis produces haploid gametes with genetic variation. Cambridge tests the purpose and outcome of each type — not the detailed phases.

What you’ll learn

Mapped to the Cambridge IGCSE 0654 syllabus (2025-2027).

B21.1 — State the role of mitosis in growth, repair, and asexual reproduction.
B21.2 — State the role of meiosis in gamete production.
B21.3 — Compare mitosis and meiosis in terms of chromosome number and genetic variation.
B21.4 — Explain how meiosis produces genetic variation.

Mitosis — Cell Division for Growth and Repair

Mitosis produces two genetically identical daughter cells with the same chromosome number as the parent cell.

Mitosis: type of cell division producing TWO daughter cells that are genetically identical to each other and to the parent cell. Daughter cells are diploid (same chromosome number as parent).

When does it occur?

Growth (increasing cell number)
Repair of damaged tissues (replacing dead cells)
Replacement of worn-out cells (e.g. red blood cells replaced every ~120 days; skin cells constantly shed)
Asexual reproduction (producing clones)

What happens:

DNA replication — chromosomes duplicated (each becomes two chromatids)
Chromatids separate to opposite poles of the cell
Cell divides → two daughter cells, each with full (diploid) chromosome set
Daughter cells are GENETICALLY IDENTICAL to parent

Cancer and mitosis: Cancer = uncontrolled cell division. Mutated genes (proto-oncogenes → oncogenes) cause cells to divide without normal regulation → tumour formation. Risk factors: smoking (chemical mutagens), UV radiation (DNA damage), viruses (insert oncogenes).

Mitosis: 2 identical diploid daughters. For growth, repair, replacement, asexual reproduction.
Daughter cells are genetically identical — same chromosome number as parent.
Cancer = uncontrolled mitosis.

Meiosis — Cell Division for Gamete Production

Meiosis produces four haploid cells with genetic variation — the process that generates the diversity needed for evolution.

Meiosis: type of cell division producing FOUR daughter cells with HALF the chromosome number (haploid). Each cell is genetically DIFFERENT from the others and from the parent.

When does it occur? ONLY in reproductive organs (testes and ovaries in animals; anthers and ovaries in plants). Produces gametes (sperm, eggs, pollen).

Two divisions in meiosis:

Meiosis I: Homologous chromosome pairs separate → 2 haploid cells (but still have doubled chromatids)
Meiosis II: Sister chromatids separate → 4 haploid cells

Sources of genetic variation in meiosis:

Independent assortment: Homologous chromosomes align randomly at the equator in Meiosis I → each gamete gets a random mix of maternal and paternal chromosomes. For humans (23 pairs) → 2²³ ≈ 8 million possible gamete types from assortment alone.
Crossing over: Homologous chromosomes exchange segments (at chiasmata) during Meiosis I → new allele combinations created.

Comparison:

Feature	Mitosis	Meiosis
Divisions	1	2
Daughter cells	2	4
Chromosome number	Diploid (2n)	Haploid (n)
Genetic variation	None (identical)	Yes
Occurs in	All body cells	Reproductive organs only
Purpose	Growth, repair	Gamete production

Meiosis: 4 haploid daughters, all genetically different. For gametes only.
Variation from: independent assortment + crossing over of homologous chromosomes.
Meiosis I separates homologous pairs; Meiosis II separates chromatids.

How it’s examined

Paper 4: 'State TWO differences between mitosis and meiosis' (2 marks — must be clear differences e.g. number of cells produced AND genetic variation). 'Explain why gametes are haploid' (2 marks — so that fertilisation produces the correct diploid number). 'State TWO ways in which meiosis produces genetic variation' (2 marks — independent assortment + crossing over). MCQ tests whether a scenario describes mitosis or meiosis.

Sources: Cambridge IGCSE Coordinated Sciences 0654 syllabus 2025-2027 (B21); 0654 Examiner Reports 2022-2024. Last reviewed 2026-05-14.

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Step-by-step worked examples — Cell Division

Step-by-step solutions to past-paper-style questions on cell division , written exactly the way a tutor would explain them at the board.

1State TWO differences between mitosis and meiosis
Extended• mitosis, meiosis, comparison
Question
State TWO differences between mitosis and meiosis.
Step-by-step solution
1. Step 1
  Number of daughter cells: mitosis produces 2 daughter cells; meiosis produces 4 daughter cells.
2. Step 2
  Genetic content: mitosis produces daughter cells that are genetically identical to the parent cell (and to each other), diploid; meiosis produces daughter cells that are genetically different, haploid.
3. Step 3
  Additional differences: mitosis = one division; meiosis = two divisions. Mitosis: growth, repair, asexual reproduction; meiosis: gamete production in reproductive organs.
Answer
Mitosis: 2 daughter cells, genetically identical, diploid. Meiosis: 4 daughter cells, genetically different, haploid. 2. Mitosis: one nuclear division; meiosis: two nuclear divisions.
2Explain why meiosis produces genetic variation but mitosis does not
Extended• meiosis, genetic variation, crossing over
Question
Explain why meiosis produces genetic variation but mitosis does not.
Step-by-step solution
1. Step 1
  In meiosis, crossing over occurs during the first division — homologous chromosomes pair up and exchange segments of DNA, producing new combinations of alleles on each chromosome.
2. Step 2
  Independent assortment: chromosomes of each homologous pair separate independently → different combinations of maternal and paternal chromosomes in each gamete.
3. Step 3
  Fertilisation (random fusion of two gametes) further increases variation.
4. Step 4
  In mitosis, DNA is copied exactly before division. Each daughter cell receives an identical set of chromosomes — no new allele combinations are formed.
Answer
Meiosis produces variation through: (1) crossing over — new allele combinations on chromosomes; (2) independent assortment — random separation of homologous pairs. Mitosis produces exact DNA copies — no new combinations, so no variation.
3Chromosome number in egg cells
Core• meiosis, haploid, gametes
Question
A person has 46 chromosomes in their skin cells. State how many chromosomes would be found in their egg cells.
Step-by-step solution
1. Step 1
  Skin cells are body (somatic) cells — they are diploid (2n = 46).
2. Step 2
  Egg cells are gametes, produced by meiosis. Meiosis halves the chromosome number → egg cells are haploid (n = 23).
Answer
23 chromosomes. Egg cells are haploid, produced by meiosis, which halves the chromosome number from 46 to 23.
4Explain why Down syndrome occurs
Extended• Down syndrome, non-disjunction, trisomy 21
Question
Explain why Down syndrome occurs in some individuals.
Step-by-step solution
1. Step 1
  During meiosis in the formation of gametes, chromosome 21 (or another pair) may fail to separate correctly — this is called non-disjunction.
2. Step 2
  One gamete ends up with two copies of chromosome 21 (instead of one). The other gamete has none.
3. Step 3
  If the gamete with two copies of chromosome 21 is fertilised by a normal gamete (one copy), the resulting zygote has three copies of chromosome 21 (trisomy 21).
4. Step 4
  The individual has 47 chromosomes instead of 46. This causes the characteristic features of Down syndrome.
Answer
Non-disjunction during meiosis causes chromosome 21 to fail to separate; a gamete with two copies of chromosome 21 is fertilised by a normal gamete; the zygote has three copies of chromosome 21 (trisomy 21) — resulting in Down syndrome (47 chromosomes total).

Key Definitions and Keywords — Cell Division

Definitions to memorise and the exact keywords mark schemes credit for cell division answers — sharpened from recent examiner reports for the 2026 0654 sitting.

Mitosis
Examiner keyword
A type of cell division producing two genetically identical diploid daughter cells from one parent cell. Used in growth, repair, and asexual reproduction.
Meiosis
Examiner keyword
A type of cell division that produces four genetically non-identical haploid daughter cells. Occurs in reproductive organs to produce gametes. Introduces genetic variation.
Diploid (2n)
Examiner keyword
A cell or organism containing two complete sets of chromosomes (one from each parent). Human body cells: 2n = 46.
Haploid (n)
Examiner keyword
A cell containing one set of chromosomes. Gametes are haploid. Human gametes: n = 23.
Mutation
Examiner keyword
A random, spontaneous change in the DNA base sequence (gene mutation) or chromosome structure/number (chromosomal mutation). Can be caused by radiation or mutagens.
Non-disjunction
Examiner keyword
The failure of homologous chromosomes (or chromatids) to separate correctly during meiosis, resulting in gametes with abnormal chromosome numbers.

Common Mistakes and Misconceptions — Cell Division

The traps other students keep falling into on cell division questions — taken from recent Cambridge IGCSE 0654 examiner reports and mark schemes — and how to avoid them.

✕Stating that gametes are produced by mitosis
0654 Examiner Report 2022
Why it happens
Students know mitosis is the common cell division and apply it to gamete production.
How to avoid it
Gametes are produced by meiosis (to halve chromosome number). Mitosis produces somatic (body) cells for growth and repair.
✕Stating that meiosis produces genetically identical cells
Why it happens
Students confuse the two types of cell division.
How to avoid it
Mitosis = identical cells. Meiosis = genetically varied cells (due to crossing over and independent assortment).
✕Stating that mutations are always harmful
Why it happens
The word 'mutation' has negative connotations in everyday language.
How to avoid it
Most mutations are neutral (no effect on phenotype). Some are harmful; a small number can be beneficial (e.g. antibiotic resistance in bacteria, sickle cell trait protecting against malaria).
✕Stating that Down syndrome is caused by an extra chromosome 21, but attributing it to the wrong cause
Why it happens
Students know it involves an extra chromosome but do not explain non-disjunction.
How to avoid it
Down syndrome = trisomy 21 caused by non-disjunction during meiosis. Always explain the mechanism: chromosome pair fails to separate → gamete with two chromosomes 21 → trisomy after fertilisation.

Practice questions

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Cell Division — frequently asked questions

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Cell Division

Short Study Notes in the form of Slides

Short Study Notes — Cell Division

Detailed Notes

What you’ll learn

How it’s examined

1State TWO differences between mitosis and meiosis

2Explain why meiosis produces genetic variation but mitosis does not

3Chromosome number in egg cells

4Explain why Down syndrome occurs

Mitosis

Meiosis

Diploid (2n)

Haploid (n)

Mutation

Non-disjunction

✕Stating that gametes are produced by mitosis

✕Stating that meiosis produces genetically identical cells

✕Stating that mutations are always harmful

✕Stating that Down syndrome is caused by an extra chromosome 21, but attributing it to the wrong cause

Practice questions

Past paper style quiz

Assess your understanding

Cell Division — frequently asked questions