Transpiration and translocation

What the syllabus asks of you

• Describe transpiration as the loss of water vapour from leaves
• Understand that water evaporates from the surfaces of the mesophyll cells into air spaces and then diffuses out of the leaves through the stomata as water vapour
• Explain: (a) the effects of wind speed, and the variation of temperature, humidity and light intensity on transpiration rate (b) how wilting occurs
• Investigate the effects of wind speed, light intensity and temperature variation on transpiration rate
• Explain the mechanism by which water moves upwards in the xylem in terms of a transpiration pull that draws up a column of water molecules, held together by forces of attraction between water molecules
• Describe translocation as the movement of sucrose and amino acids in the phloem from parts of plants that produce or release them (sources) to parts of plants that use or store them (sinks)
• Identify the positions of tissues as seen in transverse sections of non-woody dicotyledonous roots and stems, limited to: xylem, phloem and cortex
• State the functions of xylem as transport of water and mineral ions, and support
• Relate the structure of xylem vessels to their function, limited to: (a) thick walls with lignin (details of lignification are not required) (b) no cell contents (c) cells joined end-to-end with no cross walls to form a long continuous tube