Explain why red blood cells, which are placed into pure water, will eventually burst.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Red blood cells are specialised cells found in the blood. They do not have a cell wall.
Model answer (4 marks)
Red blood cells are placed in pure water, a very dilute solution. Because the cell membrane is partially permeable, water moves into the cell by osmosis from the dilute external solution to the more concentrated interior. As water enters, the cell swells and its volume increases. Red blood cells lack a rigid cell wall, so the increased internal pressure cannot be resisted and the membrane ruptures, causing the cell to burst.
Examiner tips
- Show the direction of water movement (outside to inside) and link it to osmosis.
- Explain that the lack of a cell wall means no structural support.
- Use the terms ‘swells’, ‘increases in volume’ and ‘bursts’ to match the mark scheme.
- Mention the role of the cell membrane’s permeability.
Mark scheme (4 marks)
- Water moves into the red blood cell by osmosis
- Water moves from the dilute solution (pure water) to the more concentrated solution (cell contents) through the partially permeable cell membrane
- The cell swells / increases in volume as water enters
- The cell bursts because it has no cell wall to provide support / withstand the increased pressure
Related
- Revision notes: Transport in cells →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
More Transport in cells questions
- Explain what happens to a plant cell when it is placed in a concentrated sugar s…
- Explain how oxygen moves from the air sacs (alveoli) in the lungs into the blood…
- Explain why active transport is needed to absorb mineral ions into plant root ha…
- Explain how glucose is absorbed from the small intestine into the blood when the…