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This lesson covers xylem transport and transpiration as required by the Edexcel A-Level Biology specification (9BI0). You need to understand the structure of xylem vessels, the cohesion-tension theory, factors affecting the rate of transpiration, and the use of potometers.
Plants, like large animals, have a small surface area to volume ratio relative to their metabolic needs. They require transport systems to move:
Plants have two separate transport tissues:
| Tissue | Direction of transport | Substance transported |
|---|---|---|
| Xylem | Roots → leaves (upward) | Water and dissolved mineral ions |
| Phloem | Source → sink (any direction) | Sucrose and amino acids |
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