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Transport in plants: xylem, transpiration and phloem translocation

Exchange and transport · Lesson 3 of 4

Lesson 3 of 4

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Lesson 3 of 4 · Exchange and transport

Transport in plants: xylem, transpiration and phloem translocation

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Describe the structure of xylem vessels and explain how lignified, dead, hollow cells are adapted for the transport of water and mineral ions and for support.
Explain the movement of water through roots and across plant tissues in terms of water potential gradients, including the apoplast and symplast pathways and the role of the Casparian strip in the endodermis.

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Explain transpiration as the evaporation of water from mesophyll cell walls followed by diffusion of water vapour through stomata, and relate this to the cohesion-tension mechanism of ascent of sap in xylem.

Investigate and interpret factors affecting transpiration rate, including light intensity, temperature, humidity and air movement, using potometer data with appropriate evaluation of limitations.

Describe the structure of phloem tissue, including sieve tube elements and companion cells, and explain how each is adapted to translocation.

Explain translocation in terms of the mass flow hypothesis, including active loading at sources, movement of sucrose solution by pressure gradients, and unloading at sinks.

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