A student places a red blood cell into distilled water. Describe and explain what happens to the red blood cell.

Cambridge International IGCSE Biology (0610) — 3.2 Osmosis · Describe and explain · 4 marks · View as Markdown

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

Model answer (4 marks)

Water moves into the red blood cell by osmosis.
Water moves from a region of higher water concentration (distilled water) to a region of lower water concentration (inside the cell) across the partially permeable membrane.
The cell swells and increases in volume.
The cell bursts (lyses) because it has no cell wall to resist the pressure.

Examiner tips

  • Use the word ‘osmosis’ to show understanding of the process.
  • Explain the direction of water movement using concentration terms.
  • Mention the lack of a cell wall as the reason for bursting.

Common mistakes

  • Forgetting to state that water moves by osmosis.
  • Not explaining the direction of water flow.
  • Claiming the cell will simply ‘grow’ without bursting.

Mark scheme (4 marks)

  1. Water moves into the red blood cell by osmosis
  2. Water moves from a region of higher water concentration (distilled water) to a region of lower water concentration (inside the cell) across the partially permeable membrane
  3. The cell swells / increases in volume
  4. The cell bursts / lyses because it has no cell wall to resist the pressure

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