• Evaporation and diffusion of water from a plants surface (leaves)
  • Evaporation creates a slight shortage of water so more is drawn up from the roots through the xylem cells to replace it
  • Called transpiration stream
  • A side-effect of how leaves are adapted for photosynthesis. they have to have stomata so gases can be exchanged more easily

Transpiration rate is affected by:

  • Light intensity – brighter the light, higher the transpiration rate
  • Temperature – the warmer it is, higher the transpiration rate
  • Air flow – stronger the wind, higher the transpiration rate
  • Humidity – the drier the air, higher the transpiration rate

Guard cells

  • Kidney shape – opens and closes stomata – more on bottom because shadier, less water loss
  • When plant has lots of water, guard cells fill, go plump, turgid, when is short become flaccid and close to stop too much water vapour from escaping. close at night to save water loss