Explain how the structure of the xylem is adapted to transport water from the roots to the leaves of a plant.

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 need to move water from the soil, through the roots, up the stem and into the leaves where it is used in photosynthesis. This transport is carried out by the xylem.

Model answer (5 marks)

Xylem vessels are formed from dead cells that have been hollowed out, so they contain no cytoplasm.
The end walls between adjacent vessels are removed, creating a continuous tube.
This uninterrupted pathway allows water to move from root to leaf without obstruction.
The vessel walls are thick and lignified, making them impermeable to water.
The lignin‑strengthened, water‑impermeable walls keep the water directed upwards rather than leaking into surrounding tissues.

Examiner tips

Use the word ‘hollowed out’ and ‘dead cells’ to show understanding of cell death. Mention the removal of end walls to form a continuous tube. Explain how lignin makes walls impermeable and strengthens them. Link the impermeability to directed upward flow.

Common mistakes

Forgetting that xylem cells are dead and hollow. Confusing xylem with phloem or not mentioning lignin. Failing to explain how impermeability prevents lateral leakage.

Mark scheme (5 marks)

Xylem vessels are made from hollowed-out dead cells / have no cell contents
The end walls between cells are removed / broken down, forming a continuous tube
This allows water to pass through without obstruction / allows continuous uninterrupted flow of water
The walls of the xylem are impermeable to water / strengthened with lignin
Impermeability / lignin ensures water is directed upwards rather than leaking sideways into surrounding tissue

Key terms in this question

xylem