Cells and organisation · GCSE Biology

Cell division and stem cells

The cell cycle, mitosis, meristems, embryonic and adult stem cells, and the ethics of therapeutic cloning.

UNDERSTAND→RETRIEVE→REMEMBER
THE MEMORY HOOK
Mitosis makes two identical body cells for growth and repair. Stem cells are unspecialised, so they can still become other cell types. Embryonic stem cells can become any cell; adult stem cells are more limited.

The important bits

What you need to know

  1. 1

    Before mitosis, the cell grows and replicates its DNA so there are two copies of each chromosome.

  2. 2

    Mitosis produces two daughter cells with identical sets of chromosomes. It is used for growth, repair and asexual reproduction.

  3. 3

    A stem cell is unspecialised and can divide to form specialised cells. In animals, embryonic stem cells can become any cell type; adult stem cells, for example in bone marrow, can become a limited range such as blood cells.

  4. 4

    Plant meristems in shoot and root tips contain stem cells that can differentiate into any plant tissue throughout life. This is why cuttings and tissue culture work.

  5. 5

    Stem cells can be used to treat conditions such as diabetes or paralysis in principle, and bone marrow transplants already treat blood disorders.

  6. 6

    Therapeutic cloning produces an embryo with the patient’s genes so that stem cells are not rejected. There are ethical objections to using embryos, and there is a risk of viral infection from cultured cells.

  7. 7

    Cancer is caused by uncontrolled cell division. Benign tumours stay in one place; malignant tumours invade neighbouring tissues and may form secondary tumours.

Go deeper

Mitosis is a copying process

The cell cycle is not just “the cell splits”. DNA must be copied first, otherwise each daughter cell would get half the genome. In mitosis the copies are pulled apart so each new cell receives a full, identical set of chromosomes. That is why your skin cells match your other body cells genetically. Meiosis is different: it produces gametes with half the chromosomes and introduces variation. If a question says growth of a shoot, healing a cut, or replacing blood cells, the answer is mitosis. If it says sperm, egg or variation, you have left this topic.

Go deeper

Stem cells in the exam, not in the headline

Write what the cell can still become, not a slogan. Embryonic stem cells can differentiate into any specialised cell type. Adult stem cells are already partly restricted. Plant meristem cells remain flexible, which is why a root cutting can grow a whole new plant. Evaluation questions want a balanced argument: potential to treat paralysis or diabetes, existing use in bone marrow transplants, versus destruction of embryos, religious or ethical objections, and the chance that transplanted cells could be infected or grow uncontrollably. Finish with a judgement that uses the biology.

WORKED EXAMPLE

See the idea in action

A patient with leukaemia receives a bone marrow transplant. Bone marrow contains adult stem cells that can divide and specialise into healthy white blood cells. The donor cells must be a close match so the immune system does not destroy them. This treatment already exists; using embryonic stem cells for spinal repair is still largely experimental and raises the embryo ethics question.

Exam technique

Turn knowledge into marks

Mitosis: two identical cells, growth and repair. Stem cells: unspecialised, can differentiate. In evaluation, give one medical advantage, one ethical or practical risk, and a conclusion. Do not confuse mitosis with meiosis.

Common mistakes

Do not give these marks away

  1. 01

    Saying mitosis produces gametes, or that the daughter cells are genetically different.

  2. 02

    Writing that adult stem cells can become any cell type.

  3. 03

    Giving only an ethical opinion on embryonic stem cells with no biological use or risk.

QUICK RETRIEVAL

What is the purpose of mitosis in human body cells?

ATo make gametes with half the chromosomes

BTo produce two genetically identical cells for growth and repair

CTo create variation in offspring

DTo swap genes between chromosomes

Show the answer

To produce two genetically identical cells for growth and repair. Mitosis copies the chromosomes and splits them evenly so each daughter cell matches the parent. Gametes are made by meiosis.

Quick questions

If this is the bit you searched

What is a stem cell?

An unspecialised cell that can divide and differentiate into specialised cells. Embryonic stem cells can become any type; adult stem cells are more limited.

Where are stem cells found in plants?

In meristems, especially shoot and root tips. They can differentiate into any plant tissue throughout the plant’s life.