Explain how root hair cells are adapted to absorb water and mineral ions from the soil.

WJEC A-Level Biology (Wales) — 2.4 Adaptations for nutrition · Explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Plants absorb water and mineral ions from the soil through specialised cells in their roots.

Model answer (5 marks)

Root hair cells have a very large surface area, which increases the rate of absorption of water and mineral ions from the soil.

Water is absorbed by osmosis: water moves from the soil, where the water concentration is high, into the root hair cell, where the water concentration is lower, through the partially permeable cell membrane.

Mineral ions are taken up by active transport, which moves ions against their concentration gradient. Active transport requires energy, which is supplied by cellular respiration.

Examiner tips

Show the large surface area and link it to increased absorption rate. Explain osmosis for water and active transport for ions. Mention that active transport needs energy from respiration.

Common mistakes

Forgetting to state that active transport moves ions against a gradient. Confusing diffusion with osmosis for water uptake. Omitting the role of respiration as the energy source for active transport.

Mark scheme (5 marks)

Root hair cells have a large surface area
Large surface area increases the rate of absorption / diffusion / osmosis
Water is absorbed by osmosis — movement of water from a region of high water concentration in the soil to a region of low water concentration in the root hair cell through a partially permeable membrane
Mineral ions are absorbed by active transport — movement against the concentration gradient
Active transport requires energy (from respiration)

Key terms in this question

root hair cells