Translocation (AQA GCSE Combined Science: Trilogy: Biology): Revision Note

Translocation

• The soluble products of photosynthesis are sugars (mainly sucrose) and amino acids: collectively they are referred to as cell sap

• These are transported around the plant in the phloem tubes which are made of living, elongated cells (as opposed to xylem vessels which are made of dead cells)

• Phloem tissue transports dissolved sugars from the leaves to the rest of the plant for immediate use or storage

• The cells are joined end to end and contain pores in the end cell walls (called sieve plates) which allow easy flow of substances from one cell to the next

• The transport of sucrose and amino acids in phloem, from regions of production to regions of storage or use, is called translocation

• Dissolved food is always transported from source (where it’s made) to sink (where it’s stored or used).

• Transport in the phloem goes in many different directions depending on the stage of development of the plant or the time of year

  • During winter, when many plants have no leaves storage organs are a source and other respiring tissues are sinks

  • During a growth period (e.g. during the spring), leaf buds and terminal buds are sinks

  • During the summer, the photosynthesising are a source and the roots where sugars are being stored are sinks

Diagram of translocation

Use this image

Comparing xylem and phloem tissue