Cell Division Notes

Edexcel GCSE Biology: Revision notes

Key facts

  • The cell cycle: interphase (DNA replicates), mitosis, then cytokinesis.
  • Mitosis has four stages: prophase, metaphase, anaphase, telophase.
  • It makes two genetically identical diploid daughter cells.
  • It is needed for growth, repair and asexual reproduction.
  • Cancer is uncontrolled cell division, forming a tumour.

The cell cycle

The cell cycle has three stages: interphase, mitosis and cytokinesis.

The cell cycle is the series of stages between one division and the next. In interphase the cell grows, replicates its DNA (each chromosome becomes two sister chromatids) and makes new organelles. In mitosis the nucleus divides; in cytokinesis the cytoplasm and membrane divide.

DNA replication happens in interphase, before mitosis.

  1. 1

    Interphase

    The cell grows, replicates DNA and produces new organelles.

  2. 2

    Mitosis

    The nucleus divides.

  3. 3

    Cytokinesis

    The cytoplasm and membrane divide, forming two daughter cells.

Then back to step 1

The cell cycle.

When is DNA replicated?

Stages of mitosis

Mitosis divides the nucleus in four stages, then cytokinesis splits the cytoplasm.

In prophase, chromosomes condense and the nuclear envelope breaks down. In metaphase they line up at the equator. In anaphase sister chromatids are pulled to opposite poles. In telophase the nuclear envelope re-forms around each set. Cytokinesis then splits the cytoplasm into two daughter cells.

  1. 1

    Prophase

    Chromosomes condense; nuclear envelope breaks down.

  2. 2

    Metaphase

    Chromosomes line up at the equator.

  3. 3

    Anaphase

    Sister chromatids are pulled to opposite poles.

  4. 4

    Telophase

    Nuclear envelope re-forms around each set.

  5. 5

    Cytokinesis

    The cytoplasm splits into two daughter cells.

Stages of mitosis.

In which stage are sister chromatids pulled apart?

What mitosis produces

Mitosis produces two genetically identical diploid daughter cells.

Each daughter cell has the same chromosome set as the parent: it is diploid. Do not confuse this with meiosis, which produces genetically different haploid gametes.

The stages of mitosis
Mitosis produces two daughter cells, each with the same chromosomes as the parent.

Mitosis

Cells produced:
Two daughter cells
Chromosomes:
Diploid: same set as the parent
Genetically:
Identical

Meiosis

Cells produced:
Gametes
Chromosomes:
Haploid
Genetically:
Different

How do the daughter cells of mitosis compare with the parent cell?

Why mitosis matters

Mitosis is essential for growth, repair and asexual reproduction.

A cut heals because mitosis produces new skin cells identical to the surrounding tissue.

  1. 1

    Parent cell

    copies its DNA

  2. 2

    Mitosis

    divides into two identical cells

  3. 3

    Growth and repair

    more cells, or replacement of damaged ones

  4. 4

    Asexual reproduction

    identical offspring

One mitosis, three uses.

Growth

  • Increases cell number

Repair

  • Replaces damaged cells

Asexual reproduction

  • Produces genetically identical offspring

A cut skin heals. Which process makes the new cells?

Cancer

Cancer is caused by changes in cells that lead to uncontrolled cell division.

Changes in cells cause uncontrolled mitosis. The cells form a mass of abnormal cells called a tumour. Always link cancer to uncontrolled cell division.

  1. 1

    Cell changes

    Changes in a cell affect its control of division.

  2. 2

    Uncontrolled mitosis

    The cell divides again and again.

  3. 3

    Tumour

    A mass of abnormal cells forms.

How cancer develops.

What causes cancer?

Try an exam question

Describe what happens to the chromosomes and the nucleus during mitosis.

[4 marks]

That's the notes covered.

Carry on to the next subtopic.