BiologyCode 5090
Transpiration and translocation
What this topic asks you to be able to do
- Describe transpiration as the process in which water vapour is lost from leaves
- Understand that water passes by evaporation from mesophyll cell surfaces into the air spaces, and then leaves the leaf as water vapour by diffusing out through the stomata
- Explain: (a) how wind speed, together with changes in temperature, humidity and light intensity, affects the rate of transpiration (b) the way in which wilting takes place
- Investigate how wind speed, light intensity and shifts in temperature alter the rate of transpiration
- Account for the process by which water rises through the xylem, describing it as a transpiration pull that lifts a column of water molecules, which stay joined by attractive forces between the molecules
- Outline translocation as the transport of sucrose and amino acids through the phloem, moving from sources (regions that make or release these substances) to sinks (regions that consume or store them)
- Identify where tissues lie when viewed in transverse section across non-woody dicotyledonous roots and stems, limited to: xylem, phloem and cortex
- Give the functions of xylem: conveying water and mineral ions, and providing support
- Relate the way xylem vessels are built to their function, limited to: (a) thick walls containing lignin (lignification need not be covered in detail) (b) no cell contents (c) cells linked end-to-end without any cross walls, forming a single long continuous tube