Explain how root hair cells and xylem vessels are each adapted to allow water to be transported from the soil to the leaves of a plant.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Plants must absorb water from the soil and transport it to every part of the plant. This involves two key structures: root hair cells and xylem vessels.
Model answer (5 marks)
Root hair cells have a very large surface area, which increases the rate of water uptake by osmosis.
Water enters root hair cells by osmosis, moving from a region of high water concentration in the soil to a region of lower water concentration inside the cell.
Xylem vessels are made from hollowed‑out dead cells with their end walls removed, forming a continuous tube for water to flow through.
The walls of xylem vessels are impermeable to water, so water is kept inside and flows upwards through the tube.
Xylem vessels are strengthened with lignin, which supports the plant and keeps the vessels open so water can flow freely.
Water enters root hair cells by osmosis, moving from a region of high water concentration in the soil to a region of lower water concentration inside the cell.
Xylem vessels are made from hollowed‑out dead cells with their end walls removed, forming a continuous tube for water to flow through.
The walls of xylem vessels are impermeable to water, so water is kept inside and flows upwards through the tube.
Xylem vessels are strengthened with lignin, which supports the plant and keeps the vessels open so water can flow freely.
Examiner tips
- Use the exact terms ‘large surface area’, ‘osmosis’, ‘hollowed‑out dead cells’, ‘impermeable walls’, and ‘lignin’ as these are the key phrases the mark scheme looks for.
- Structure the answer in five clear points, each addressing one of the scheme points.
- Show the direction of water movement (soil to cell) to demonstrate understanding of osmosis.
- Mention that lignin provides mechanical support to keep vessels open.
Mark scheme (5 marks)
- Root hair cells have a large surface area, which increases the rate of water uptake by osmosis.
- Water enters root hair cells by osmosis, moving from a region of high water concentration in the soil to a region of lower water concentration inside the cell.
- Xylem vessels are made from hollowed-out dead cells with their end walls removed, forming a continuous tube for water to flow through.
- Xylem vessel walls are impermeable to water, so water is kept inside and flows upwards through the tube.
- Xylem vessels are strengthened with lignin, which supports the plant and keeps the vessels open so water can flow freely.
Key terms in this question
Related
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