Transpiration

• What is transpiration?

  Evaporation of water from mesophyll cells
• How does transpiration occur in leaves?

  Through diffusion via air spaces and stomata
• What apparatus is used to measure transpiration rates?

  A potometer
• What does a potometer measure?

  The rate of water uptake by a cut shoot
• Why is a potometer not accurate for measuring transpiration?

  Some water is used and does not evaporate
• How is the bubble potometer set up?

  A cut shoot is placed underwater
• What does the weight potometer measure?

  The loss in mass of a pot plant
• How long should a plant be on a balance for the weight potometer?

  At least 24 hours
• What must be covered to prevent evaporation in the weighing method?

  The compost around the shoot
• What is the purpose of the washing line method?

  To compare water loss in different conditions
• How are leaves prepared for the washing line method?

  They are detached, numbered, and weighed
• What environmental factors affect transpiration rates?

  Temperature, wind speed, humidity, light/darkness
• How does temperature affect transpiration?

  Warmer conditions increase evaporation rates
• What effect does wind speed have on transpiration?

  Higher wind speeds increase evaporation rates
• How does humidity affect transpiration?

  High humidity restricts evaporation rates
• What happens to stomata in darkness?

  Many plants close stomata to reduce water loss
• How does leaf surface area affect transpiration rates?


  Larger surface area increases transpiration rates
• What are the steps to use a potometer for measuring transpiration?


  • Set up the potometer with a cut shoot
  • Place the apparatus underwater to remove air bubbles
  • Measure the rate of water uptake
  • Create different environmental conditions for comparison
• What are the factors affecting the rate of transpiration?


  • Temperature: warmer conditions increase evaporation
  • Wind speed: higher speeds enhance evaporation
  • Humidity: high humidity decreases evaporation
  • Light/darkness: stomata close in darkness
  • Surface area: larger areas increase transpiration