Explain why water moves out of a plant root hair cell when it is placed in a concentrated salt solution.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A plant root hair cell contains a dilute solution inside its vacuole. When the cell is placed in a concentrated salt solution, water moves out of the cell.
Model answer (4 marks)
Osmosis is the process by which water moves.
Water moves from an area of high water concentration to an area of low water concentration.
The concentrated salt solution outside the cell has a lower water concentration than the dilute solution inside the vacuole.
Water therefore moves out of the cell through the partially permeable plasma membrane.
Water moves from an area of high water concentration to an area of low water concentration.
The concentrated salt solution outside the cell has a lower water concentration than the dilute solution inside the vacuole.
Water therefore moves out of the cell through the partially permeable plasma membrane.
Examiner tips
- Use the term "osmosis" first. Explain the direction of movement using "high to low water concentration". State that the external solution has a lower water concentration. Mention the membrane is partially permeable to water.
Common mistakes
- Confusing solute concentration with water concentration. Saying water moves into the cell instead of out. Omitting that the membrane is partially permeable.
Mark scheme (4 marks)
- The process by which water moves is osmosis
- Water moves from a region of high water concentration to a region of low water concentration
- The salt solution outside has a lower water concentration than the cell contents
- Water moves out through the partially permeable membrane
Related
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