Explain why a cell must copy its chromosomes before mitosis can occur.

AQA GCSE Biology (8461) — 4.1.2 Cell division · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Chromosomes carry the cell’s DNA, which contains all the genes required for its functions.

Before a cell enters mitosis, the chromosomes must be duplicated so that each daughter cell will receive a complete set of chromosomes.

If the chromosomes were not copied, each daughter cell would inherit only half the genetic material, leading to a loss of genes.

Duplicating the chromosomes ensures that the two daughter cells are genetically identical to the parent cell and that the correct genetic information is passed on.

Examiner tips

  • Use the term ‘chromosomes’ and ‘DNA’ early. Show the logical sequence: DNA → duplication → mitosis → identical daughters. Mention loss of genes if not duplicated. Keep answer concise, 4 points.
  • common_mistakes
  • :
  • Confusing mitosis with meiosis. Failing to state that each daughter cell must receive a full set of chromosomes. Using vague phrases like ‘copying the cell’ instead of ‘duplicating the chromosomes.’

Mark scheme (4 marks)

  1. Chromosomes contain the genetic material / genes / DNA of the cell
  2. Mitosis produces two daughter cells that must each receive a full set of chromosomes
  3. If chromosomes were not copied first, each daughter cell would only receive half the number of chromosomes
  4. The daughter cells are genetically identical to the parent cell / copying ensures the correct genetic information is passed on

Key terms in this question

chromosomes · mitosis

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