A student places a plant cell into a concentrated sugar solution. Describe what happens to the plant cell, using the terms turgid, flaccid, plasmolysis and partially permeable membrane in your answer.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
The sugar solution is more concentrated than the cell, so water moves out of the cell by osmosis.
Water moves from a region of higher water concentration (inside the cell) to a region of lower water concentration (the surrounding solution) across the partially permeable membrane.
The cell loses water and becomes flaccid – its volume decreases and the cytoplasm shrinks.
If water continues to leave, plasmolysis occurs – the cytoplasm pulls away from the cell wall.
Water moves from a region of higher water concentration (inside the cell) to a region of lower water concentration (the surrounding solution) across the partially permeable membrane.
The cell loses water and becomes flaccid – its volume decreases and the cytoplasm shrinks.
If water continues to leave, plasmolysis occurs – the cytoplasm pulls away from the cell wall.
Examiner tips
- Use the exact terms turgid, flaccid, plasmolysis, partially permeable membrane.
- Show the direction of water movement and the cause (concentrated solution).
- Explain the change in cell state (flaccid to plasmolysis).
Common mistakes
- Confusing turgid with flaccid; describing the cell as turgid when it has lost water.
- Omitting the term partially permeable membrane or the direction of water movement.
- Not mentioning plasmolysis or describing it incorrectly.
Mark scheme (4 marks)
- The solution is more concentrated than the cell contents, so water moves out of the cell by osmosis
- Water moves from a region of higher water concentration (inside the cell) to a region of lower water concentration (the surrounding solution) across the partially permeable membrane
- The cell loses water and becomes flaccid (the volume of the cell decreases / the cytoplasm shrinks)
- If water continues to leave, plasmolysis occurs — the cytoplasm pulls away from the cell wall
Key terms in this question
partially permeable membrane · turgid · flaccid · plasmolysis
Related
- All Cambridge International IGCSE Biology (0610) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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