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7. Plant Transport

  • Why do organisms with a small surface area to volume ratio need a transport system?
  • How is xylem and phloem distributed in the roots, stems and leaves of dicotyledonous plants?
  • What is the structure and function of xylem vessels, sieve tube elements and companion cells?
  • Can you explain the movement of water between plant cells, and between plant cells and their environment, using the term water potential?
  • Can you explain how water is transported from the root cortex to the air surrounding the leaves – with reference to adhesion, cohesion and the transpiration stream?
  • What is transpiration?
  • Why is transpiration a consequence of gaseous exchange?
  • What factors affect transpiration rate?
  • How is a potometer used to estimate transpiration rates?
  • How are the leaves of some xerophytes adapted to reduce water loss?
  • What is translocation?
  • Can you explain how the mechanism of transport in phloem involves active loading at the source, and removal at the sink? Can you state the evidence for and against this mechanism?
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