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Teacher Information: Transpiration

Answers to Questions:

1. It is typically predicted that the light and wind will increase the rate of transpiration. This may not be apparent until after correction for surface area differences. Sometimes the wind, if too strong, may cause the leaves to droop or fold up and in this case they may transpire less. Stomates may close to counter the dehydration. If this happens, discuss the nature of science experimentation, e.g., the expected may not always be the result. Usually, after correction for surface area, the high humidity plant will transpire less than a control. A student may question whether the light increased the temperature of the leaf. If the light was too close the plant, temperature may indeed be a variable without a control.
2. Answers will vary - usually the light will produce the greatest rate of water loss. High light intensity increases water loss due to increased photosynthesis. Wind removes water vapor from the surface of the leaf more rapidly. It may increase the evaporation rate by increasing the gradient between water in the leaf air spaces and water vapor in the air.
3. Plants can increase or decrease water loss by:
   • Closing the stomata during water stress.
   • Reducing the number of stomata.
   • Waxy cuticles.
   • Fleshy, thick leaves.
   • Hairy surfaces.
   • Reducing the overall leaf surface area.

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