CIE IGCSE Biology: 复习笔记:8.1.6 Transpiration Stream: Extended

CIE IGCSE Biology: 复习笔记:8.1.6 Transpiration Stream: Extended

Water Vapour Loss: Extended

  • Evaporation takes place from the surfaces of spongy mesophyll cells
  • The many interconnecting air spaces between these cells and the stomata create a large surface area
  • This means evaporation can happen rapidly when stomata are open

Transpiration Stream: Extended

  • Water molecules are attracted to each other by cohesion - creating a continuous column of water up the plant
  • Water moves through the xylem vessels in a continuous transpiration stream from roots to leaves via the stem
  • Transpiration produces a tension or ‘pull’ on the water in the xylem vessels by the leaves
  • As water molecules are held together by cohesive forces (each individual molecule ‘pulls’ on the one below it), so water is pulled up through the plant
  • If the rate of transpiration from the leaves increases, water molecules are pulled up the xylem vessels quicker


The generation of the transpiration stream.