Explain how water moves from the soil into the xylem of a plant root, and describe the role of xylem tissue in transporting water through the plant.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Plants absorb water from the soil and transport it to their leaves. This process involves several specialised tissues working together.
Model answer (5 marks)
Water enters the root hairs by osmosis from the soil into the epidermal cells.
Water then moves cell‑to‑cell through the cortex, following a water‑potential gradient that drives it toward the xylem.
The xylem vessels are long, hollow, dead cells with no end walls, forming a continuous tube that allows water to travel unimpeded.
Xylem therefore transports water and dissolved mineral ions from the roots up through the stem to the leaves.
At the leaf surface water evaporates (transpiration), creating a negative pressure that pulls more water up through the xylem.
Water then moves cell‑to‑cell through the cortex, following a water‑potential gradient that drives it toward the xylem.
The xylem vessels are long, hollow, dead cells with no end walls, forming a continuous tube that allows water to travel unimpeded.
Xylem therefore transports water and dissolved mineral ions from the roots up through the stem to the leaves.
At the leaf surface water evaporates (transpiration), creating a negative pressure that pulls more water up through the xylem.
Examiner tips
- Use the word ‘osmosis’ for root‑hair uptake; mention water‑potential gradient for cortex movement. Describe xylem vessels as hollow, dead cells without end walls. Explain that transpiration creates a pull that drives upward transport.
Common mistakes
- Confusing diffusion with osmosis for root‑hair uptake. Forgetting to mention the continuous tube nature of xylem vessels. Overlooking the role of transpiration in pulling water up.
Mark scheme (5 marks)
- Water enters root hair cells by osmosis
- Water moves from cell to cell across the root cortex because there is a water potential gradient (towards the xylem)
- Xylem vessels are hollow/dead cells with no end walls, forming a continuous tube
- Xylem transports water (and mineral ions) up the plant from roots to leaves
- Water evaporates from the leaves (transpiration) which pulls more water up through the xylem
Key terms in this question
Related
- All Pearson Edexcel A-Level Biology A (9BI0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
More Plant structure and function questions
- Explain how meristem tissue enables a plant to grow. In your answer, refer to bo…
- Guard cells control gas exchange in plant leaves. Explain how the structure of g…
- A student investigating plant growth cuts off all the leaves from a young plant.…
- Phloem tissue transports sugars around a plant. Explain how the structure of phl…