Explain why the leaves of a plant act as a source during translocation, and name two regions of the same plant that would act as sinks.

Cambridge International IGCSE Biology (0610) — 8.4 Translocation · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

Leaves produce sucrose and amino acids by photosynthesis, so they are the source.
The sucrose is loaded into the phloem and transported away from the leaves.
Two sink regions are the roots and the developing fruits.

Examiner tips

Use the term ‘source’ for leaves and ‘sink’ for other organs. Show the transport route via the phloem. Name two different sinks – e.g. roots and fruits – to gain full marks.

Common mistakes

Calling the leaves a sink instead of a source. Only naming one sink or repeating the same organ twice. Using vague terms like ‘other parts’ without specifying sinks.

Mark scheme (4 marks)

Leaves produce / synthesise sucrose and/or amino acids (by photosynthesis)
These substances are transported away from the leaves (to other parts of the plant) via the phloem
One correct named sink region (e.g. roots / buds / fruits / growing regions / storage organs)
A second, different correct named sink region

Key terms in this question

translocation · source · sink