Mitosis is a type of cell division that occurs during the cell cycle. Explain why mitosis is important to a multicellular organism, and describe what happens to the DNA of a cell during the cell cycle before mitosis takes place.

WJEC A-Level Biology (Wales) — 1.2 Cell structure and organisation · Explain · 5 marks · View as Markdown

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

Model answer (5 marks)

Mitosis is essential for a multicellular organism because it enables growth by producing new cells and it replaces or repairs damaged or old cells, ensuring tissue maintenance. During interphase, before mitosis, the cell grows and increases its organelle number. The DNA is also replicated, producing two identical copies of each chromosome so that each daughter cell receives a complete genome.

Examiner tips

  • Use the word ‘growth’ and ‘repair’ to hit the first two marks; mention ‘identical DNA’ for the third; describe interphase growth and organelle increase for the fourth and fifth marks.
  • Include the phrase ‘DNA is replicated’ – examiners look for this exact wording.
  • Keep the answer brief and structured to match the five points.

Common mistakes

  • Confusing meiosis with mitosis; describing gamete formation instead of somatic cell division.
  • Omitting the replication step or saying the DNA is ‘divided’ rather than ‘replicated’.
  • Failing to mention organelle increase or cell growth during interphase.

Mark scheme (5 marks)

  1. Mitosis allows the organism to grow
  2. Mitosis allows replacement / repair of old or damaged cells
  3. Mitosis produces two daughter cells with identical copies of DNA
  4. During interphase (before mitosis), the DNA is replicated / copied
  5. The number of organelles also increases / the cell grows during interphase

Key terms in this question

mitosis · cell cycle · DNA

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