Root hair cells are adapted to absorb water and mineral ions from the soil. Explain how root hair cells are adapted for this function, and describe the processes by which water and mineral ions enter the root hair cell.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
Root hair cells have a long, thin extension that greatly increases their surface area, allowing more contact with the soil.
Water enters the cell by osmosis: water moves from the soil, where the water potential is higher, into the cell, where the water potential is lower, through the semi‑permeable plasma membrane.
Mineral ions are taken up by active transport. Active transport moves ions against their concentration gradient, from the low concentration in the soil to the high concentration inside the cell, and it requires energy derived from cellular respiration.
Water enters the cell by osmosis: water moves from the soil, where the water potential is higher, into the cell, where the water potential is lower, through the semi‑permeable plasma membrane.
Mineral ions are taken up by active transport. Active transport moves ions against their concentration gradient, from the low concentration in the soil to the high concentration inside the cell, and it requires energy derived from cellular respiration.
Examiner tips
- Mention the large surface area first; link it to increased absorption. Explain osmosis as net movement from high to low water potential. State that mineral ions use active transport and that it requires ATP from respiration.
Common mistakes
- Failing to mention the increased surface area of root hairs. Confusing passive diffusion for the uptake of mineral ions. Omitting that active transport requires energy from respiration.
Mark scheme (5 marks)
- Root hair cells have a large surface area (due to the hair-like extension)
- Water enters by osmosis — net movement from a region of high water concentration (soil) to a region of low water concentration (cell) through a partially permeable membrane
- Mineral ions enter by active transport
- Active transport moves mineral ions against the concentration gradient (from low concentration in soil to high concentration in the cell)
- Active transport requires energy (from respiration)
Key terms in this question
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