Explain how the structure of root hair cells makes them well adapted for absorbing water and minerals from the soil.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Plants absorb water and minerals through root hair cells. These cells are found just behind the growing tip of roots and are in direct contact with the soil.
Model answer (4 marks)
Root hair cells have a very long, thin shape that gives them a large surface area relative to their volume.
The large surface area allows more water to enter the cell by osmosis, because the rate of diffusion/osmosis is proportional to the area across which it occurs.
Water moves into the cell by osmosis, down the concentration gradient from the high water concentration in the soil to the lower concentration inside the root hair cell.
Minerals are taken up by active transport, which moves ions against their concentration gradient and therefore requires energy (ATP).
The large surface area allows more water to enter the cell by osmosis, because the rate of diffusion/osmosis is proportional to the area across which it occurs.
Water moves into the cell by osmosis, down the concentration gradient from the high water concentration in the soil to the lower concentration inside the root hair cell.
Minerals are taken up by active transport, which moves ions against their concentration gradient and therefore requires energy (ATP).
Examiner tips
- Use the word "large surface area" and link it to increased rate of absorption. Explain osmosis as movement down a concentration gradient. Mention active transport for minerals and that it requires energy. Keep the answer concise and use the exact terminology from the mark scheme.
Common mistakes
- Confusing passive diffusion with osmosis. Forgetting to state that active transport moves minerals against a concentration gradient. Using vague terms like "more water" without explaining the mechanism.
Mark scheme (4 marks)
- Root hair cells have a large surface area
- Large surface area increases the rate of absorption / diffusion / osmosis
- Water enters by osmosis (down a concentration gradient / from high water concentration in soil to low water concentration in root hair cell)
- Minerals are absorbed by active transport (against the concentration gradient / requires energy)
Key terms in this question
Related
- Revision notes: Supplying the cell →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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