Describe the role of the phloem in a flowering plant, including the substances transported and the direction of movement.

Pearson Edexcel International GCSE Biology (4BI1) — 2.10 Transport: flowering plants · Describe · 4 marks · View as Markdown

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

Model answer (4 marks)

Phloem is the tissue that transports sucrose (and sometimes amino acids) throughout a flowering plant.

It carries these substances in both directions, moving material from the source (e.g. leaves where photosynthesis occurs or storage tissues) to the sink (e.g. roots, growing shoots, fruits or seeds).

This bidirectional movement of sugars and other nutrients is called translocation.

Examiner tips

  • Use the term "phloem" and "translocation". Mention both sucrose and amino acids. State source and sink clearly. Show bidirectional movement.

Common mistakes

  • Confusing phloem with xylem. Forgetting to mention the direction (source to sink). Using vague terms like "nutrients" without specifying sucrose or amino acids.

Mark scheme (4 marks)

  1. Phloem transports sucrose (and/or amino acids) through the plant.
  2. Transport in phloem occurs in both directions / from source to sink.
  3. Substances move from areas where they are made or stored (source, e.g. leaves) to areas where they are needed or used (sink, e.g. roots, growing regions, fruits).
  4. This process is called translocation.

Key terms in this question

phloem

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