Translocation: Phloem

While the xylem transports water and minerals upward from the roots, the phloem transports dissolved organic substances — primarily sucrose and amino acids — around the plant. This process is called translocation. This lesson covers the structure of phloem, the mechanism of translocation, and the key differences between xylem and phloem, as required by Edexcel GCSE Biology (1BI0) Topic 6.

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What is Translocation?

Translocation is the transport of dissolved sugars (mainly sucrose) and other organic molecules such as amino acids through the phloem tissue of a plant.

Why Sucrose?

Plants convert glucose (made by photosynthesis) into sucrose for transport because:

• Sucrose is more chemically stable than glucose — it is less reactive and less likely to be broken down during transport
• Sucrose is a disaccharide (made of glucose + fructose) — it is soluble in water, making it easy to transport as a dissolved solution
• At the destination, sucrose is converted back to glucose (or other molecules) for use by cells

Exam Tip: In exams, be specific — phloem transports sucrose (not "sugar" or "glucose"). The mark scheme usually requires the word "sucrose".

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Sources and Sinks