What is mitosis and why is it important in the context of inheritance?

Mitosis is a type of cell division that results in two genetically identical daughter cells from a single parent cell. It is crucial for growth, repair, and asexual reproduction in organisms. In the context of inheritance, mitosis ensures that each daughter cell receives an exact copy of the parent cell's DNA, maintaining genetic consistency across cells.

How does mitosis differ from meiosis in terms of genetic inheritance?

Mitosis and meiosis are both forms of cell division, but they serve different purposes. Mitosis results in two identical daughter cells and is involved in growth and repair, while meiosis produces four genetically diverse gametes for sexual reproduction. Meiosis introduces genetic variation through processes like crossing over, which is not a feature of mitosis.

What are the main stages of mitosis and what happens in each stage?

Mitosis consists of four main stages: prophase, metaphase, anaphase, and telophase. In prophase, chromosomes condense and become visible, and the nuclear envelope breaks down. During metaphase, chromosomes align at the cell's equator. In anaphase, sister chromatids are pulled apart to opposite poles of the cell. Finally, in telophase, nuclear membranes reform around each set of chromosomes, and the cell begins to divide.

Why is mitosis considered a key process in the IB MYP Science curriculum?

Mitosis is a fundamental biological process that is essential for understanding growth, development, and genetic stability in organisms. In the IB MYP Science curriculum, studying mitosis helps students grasp key concepts of cell biology and inheritance, providing a foundation for more advanced topics in genetics and molecular biology.

How can errors in mitosis affect an organism's genetic inheritance?

Errors in mitosis, such as nondisjunction or chromosome missegregation, can lead to cells with abnormal numbers of chromosomes, a condition known as aneuploidy. This can result in genetic disorders or diseases, such as cancer. Understanding these errors is important for studying genetic inheritance and the implications of cellular malfunction in the IB MYP Science curriculum.

Why is "Confusing mitosis with meiosis." a common mistake in Mitosis?

Why it happens: Names sound similar. How to avoid it: MITOSIS: 2 IDENTICAL cells; MEIOSIS: 4 UNIQUE cells. Mitosis = body cells; meiosis = sex cells.

Why is "Mixing the order of P-M-A-T." a common mistake in Mitosis?

Why it happens: Many stages. How to avoid it: Mnemonic: P-M-A-T. 'Prophase Means Anyone Telephone'. Or 'Please Mind All Tropics'.

InheritanceIB MYP Sciences (Years 1-5)

Mitosis

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Mitosis — IB MYP Sciences: how one cell becomes two identical daughter cells

Mitosis is the cell division that produces two GENETICALLY IDENTICAL cells. It's how you grow, heal and replace worn-out cells. This MYP Sciences note covers the purpose, the four stages, and the difference from meiosis.

What you’ll learn

Mapped to the IB MYP Sciences subject guide (2026 onwards).

MYP Sciences A — State the purpose of mitosis and the number of daughter cells produced.
MYP Sciences A — Name the four stages of mitosis.
MYP Sciences A — Contrast mitosis with meiosis.
MYP Sciences D — Link uncontrolled mitosis to cancer.

Purpose and stages of mitosis

One cell → two identical cells. Four stages: P-M-A-T.

Mitosis is the type of cell division that produces TWO GENETICALLY IDENTICAL daughter cells. Each has the SAME number of chromosomes as the original parent cell (46 in humans).

Purposes:

Growth — a baby grows from a single cell into trillions, all by repeated mitosis.
Repair — when you cut your skin, mitosis builds new cells to close the wound.
Replacement — your gut lining renews every few days, your blood cells every few months.
Asexual reproduction — bacteria, some plants and a few animals reproduce by mitosis alone.

Before mitosis starts, the cell COPIES all its DNA. Each chromosome becomes a pair of identical 'sister chromatids' joined at the centre.

Four stages of mitosis (mnemonic: P-M-A-T):

Prophase: chromosomes condense and become visible; nuclear membrane breaks down.
Metaphase: chromosomes line up across the MIDDLE of the cell.
Anaphase: sister chromatids pulled APART to opposite ends.
Telophase: two new nuclear membranes form; chromosomes uncoil.

Then cytokinesis splits the cytoplasm — and you have two daughter cells.

One cell → 2 IDENTICAL cells, both with full chromosome set.
DNA replicates BEFORE mitosis starts.
Four stages: Prophase, Metaphase, Anaphase, Telophase (P-M-A-T).
Used for growth, repair, replacement, asexual reproduction.

Cancer — mitosis out of control

Cancer cells divide uncontrollably and don't stop.

Healthy cells divide only when needed. The cell cycle has CHECKPOINTS — proteins that decide whether a cell should proceed to divide or pause to fix problems first.

If the genes controlling these checkpoints are damaged (by mutation), the cell may divide CONTINUOUSLY → forming a TUMOUR. If the tumour cells stay put it's BENIGN (often harmless). If they spread to other parts of the body it's MALIGNANT (cancerous).

What causes the damage?

Carcinogens: chemicals that mutate DNA (e.g. tobacco smoke compounds, some industrial solvents, asbestos fibres).
Radiation: UV from sunbeds and the sun, X-rays in high doses, gamma rays.
Some viruses: HPV → cervical cancer; hepatitis B/C → liver cancer.
Inherited mutations: BRCA1/2 genes increase breast/ovarian cancer risk.
Age and chance: random replication errors accumulate over time.

Cancer TREATMENT often aims to kill rapidly-dividing cells:

Chemotherapy: drugs that damage replicating DNA.
Radiotherapy: targeted radiation kills tumour cells.
Surgery: removes the tumour.
Immunotherapy: helps the immune system recognise cancer cells.

MYP criterion D classic: 'Discuss the ethics and challenges of cancer treatment.' Strong answers cover: side effects (chemo affects healthy cells too), early detection, lifestyle prevention, cost and access.

Cancer = uncontrolled mitosis.
Causes: carcinogens, radiation, some viruses, mutations.
Treatments target rapidly-dividing cells (chemo) or use radiation/surgery.

Mitosis vs meiosis

Two completely different kinds of cell division.

Feature	MITOSIS	MEIOSIS
Number of daughter cells	2	4
Chromosome number per daughter	Same as parent (46 in humans = diploid)	HALF the parent (23 = haploid)
Genetic identity to parent	Identical	All different — and different from each other
Purpose	Growth, repair, replacement	Making sex cells (sperm and egg) for sexual reproduction
Where it happens	Most body cells	Testes and ovaries only

So mitosis is the workhorse for body growth and repair. Meiosis is the special division for producing gametes — which fuse during fertilisation to restore the chromosome number in the new individual.

This is why sexual reproduction creates VARIETY: each sex cell has a unique random combination of the parent's chromosomes, and fertilisation joins two such random combinations. Asexual reproduction (by mitosis only) gives clones.

Mitosis: 2 identical daughters, full chromosome set. Body cells.
Meiosis: 4 unique daughters, HALF chromosome set. Sex cells only.
Mitosis = clones; meiosis = variety.

How it’s examined

Criterion A asks for purpose, stages and contrast with meiosis. Criterion D often asks about cancer or stem cell ethics.

Sources: IB MYP Sciences guide (IBO, official subject guide). Last reviewed 2026-05-25.

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Step-by-step worked examples — Mitosis

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

1Order of mitosis stages
Getting started• stages
Question
List the four stages of mitosis in order.
Step-by-step solution
1. Step 1
  P-M-A-T: Prophase, Metaphase, Anaphase, Telophase.
Answer
Prophase, Metaphase, Anaphase, Telophase.
2Why mitosis matters
Building confidence• purpose
Question
Give three roles of mitosis in the human body.
Step-by-step solution
1. Step 1
  GROWTH — a fertilised egg becomes ~37 trillion cells by mitosis.
2. Step 2
  REPAIR — wound healing depends on mitosis to make replacement cells.
3. Step 3
  REPLACEMENT — gut lining, skin and blood cells are constantly worn out and replaced.
Answer
Growth, repair (healing), and replacement of worn-out cells.
3Why cancer is dangerous
Stretch• cancer
Question
Explain why cancer is described as 'uncontrolled mitosis'.
Step-by-step solution
1. Step 1
  Normally, cells only divide when needed — checkpoint genes regulate the cell cycle.
2. Step 2
  If those genes are damaged by mutation, cells keep dividing without stopping.
3. Step 3
  This forms tumours. Malignant tumours can spread, disrupting organs and ultimately threatening life.
Answer
Mutations in regulator genes remove checkpoints → cells divide endlessly → tumours form → if malignant, they spread and disrupt organs.

Key Definitions and Keywords — Mitosis

Definitions to memorise and the exact keywords mark schemes credit for mitosis answers — sharpened from recent examiner reports for the 2026 IB MYP Sciences sitting.

Mitosis
Examiner keyword
Cell division producing two genetically identical daughter cells with the full chromosome number.
Diploid
Examiner keyword
Having two complete sets of chromosomes (46 in humans). Most body cells.
Haploid
Examiner keyword
Having one set of chromosomes (23 in humans). Sex cells (sperm and egg).
Meiosis
Examiner keyword
Cell division producing four genetically unique haploid daughter cells (sex cells).

Common Mistakes and Misconceptions — Mitosis

The traps other students keep falling into on mitosis questions — taken from recent IB MYP Sciences examiner reports and mark schemes — and how to avoid them.

✕Confusing mitosis with meiosis.
Why it happens
Names sound similar.
How to avoid it
MITOSIS: 2 IDENTICAL cells; MEIOSIS: 4 UNIQUE cells. Mitosis = body cells; meiosis = sex cells.
✕Mixing the order of P-M-A-T.
Why it happens
Many stages.
How to avoid it
Mnemonic: P-M-A-T. 'Prophase Means Anyone Telephone'. Or 'Please Mind All Tropics'.

Practice questions

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Mitosis — frequently asked questions

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Mitosis

Short Study Notes in the form of Slides

Short Study Notes — Mitosis

Detailed Notes

What you’ll learn

How it’s examined

1Order of mitosis stages

2Why mitosis matters

3Why cancer is dangerous

Mitosis

Diploid

Haploid

Meiosis

✕Confusing mitosis with meiosis.

✕Mixing the order of P-M-A-T.

Practice questions

Past paper style quiz

Assess your understanding

Mitosis — frequently asked questions