Explain how the structure of a root hair cell is adapted for the absorption of water and mineral ions from the soil.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Root hair cells have a long, thin hair‑like extension that greatly increases the surface area of the cell membrane in contact with soil water.
They contain a large central vacuole with concentrated cell sap, lowering the water potential inside the cell and creating a gradient that drives water into the cell by osmosis.
The plasma membrane is rich in protein carrier and transporter proteins (ion channels and pumps) that actively move mineral ions into the cell against their concentration gradients.
Many mitochondria supply ATP via aerobic respiration to power these active transport processes.
They contain a large central vacuole with concentrated cell sap, lowering the water potential inside the cell and creating a gradient that drives water into the cell by osmosis.
The plasma membrane is rich in protein carrier and transporter proteins (ion channels and pumps) that actively move mineral ions into the cell against their concentration gradients.
Many mitochondria supply ATP via aerobic respiration to power these active transport processes.
Examiner tips
- Use the word ‘adapted’ to link structure to function; mention surface area, vacuole, transport proteins, and mitochondria.
- Show the water potential gradient and active transport explicitly; include ATP source.
- Keep each point concise and use exam‑specific terminology.
Mark scheme (4 marks)
- Root hair cells have a long, thin hair-like extension that greatly increases the surface area of the cell membrane in contact with soil water.
- Root hair cells have a large central vacuole containing a concentrated cell sap, which lowers the water potential inside the cell, maintaining a water potential gradient so water enters by osmosis.
- Root hair cells possess a high density of protein carrier / transporter proteins (ion channels / pumps) in their plasma membrane for the active transport of mineral ions against their concentration gradient.
- Root hair cells contain many mitochondria to provide ATP (via aerobic respiration) to power the active transport of mineral ions.
Key terms in this question
Related
- All IB DP Biology Standard Level (2023 syllabus) revision notes →
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- Decode the mark scheme abbreviations →
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