Explain how translocation moves sugars from a source to a sink in a plant.

Cambridge International IGCSE Biology (0610) — 8.1 Xylem and phloem · Explain · 4 marks · View as Markdown

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

A farmer grows tomato plants. During the growing season, sucrose produced in the leaves is transported to the developing fruits.

Model answer (4 marks)

Translocation occurs in the phloem.
Leaves act as the source where sucrose is produced.
Fruits (or roots, storage organs or growing regions) act as the sink where sugars are stored or used.
Translocation requires energy and is an active process.

Examiner tips

Use the exact terms ‘source’ and ‘sink’ and mention the phloem; this shows knowledge of the system.
Explain that the movement is driven by an active process – a key point for full marks.
Keep the answer short and to the point – examiners look for concise, accurate statements.
Mention that the source produces sucrose and the sink consumes or stores it – this links the two concepts.

Common mistakes

Confusing xylem with phloem; students may say ‘xylem transports sugars’. Using vague language like ‘sugar moves’ without specifying source/sink. Omitting that translocation is an active, energy‑requiring process.

Mark scheme (4 marks)

Translocation occurs in the phloem
Leaves act as the source (where sucrose is produced)
Fruits (or roots / storage organs / growing regions) act as the sink (where sugars are stored or used)
Translocation requires energy / is an active process

Key terms in this question

translocation · source · sink