Transport in Plants: Phloem and Translocation

This lesson covers phloem transport and translocation as required by the Edexcel A-Level Biology specification (9BI0). You need to understand the structure of phloem tissue, the mechanism of translocation (the mass flow hypothesis), the concepts of sources and sinks, and the evidence supporting the mass flow hypothesis.

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Structure of Phloem

Phloem is a living transport tissue that carries dissolved organic solutes — primarily sucrose and amino acids — from where they are produced (sources) to where they are needed (sinks).

Sieve Tube Elements

Sieve tube elements are the main conducting cells in phloem. They are arranged end to end to form sieve tubes.