Transpiration Investigations

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A couple of simple investigations around "Transpiration" would be looking at how light affects transpiration and how temperature affects transpiration.


Transpiration Demonstration

  • Identify a single plant (e.g. a salal bush).
  • Securely fasten a plastic bag over one leaf of the plant using a twist tie.
  • Cover the bottom side of another leaf with vasoline. This will block the stomata from releasing water. Securely fasten a plastic bag around this leaf with a twist tie.
  • The next day, return to the plant. Water should have evaporated out of the stomata of the leaf that was not covered in vasoline, so you should see water on the inside of the bag. The vasoline should have blocked evaporation from the stomata on the other leaf, and you should see no water inside the bag.


How Does Light affect Transpiration

  • Have students make a prediction if there are differences in transpiration rates in light or dark conditions.
  • In the morning, select 2 similar-sized plants of the same species. Securely fasten a plastic bag around a branch of each plant. Cover one plant with a tarp. At the end of the day, check to see how much water has collected in each of the plastic bags.
  • Which bag has more water collected in it?


How does temperature affect transpiration?

  • Have students make a prediction if there are differences in transpiration rates in warm or cool conditions.
  • In the morning, select two similar sized plants, one in the greenhouse and one outside. Securely fasten a plastic bag around a branch of each plant. Measure the air temperature by each plant. At the end of the day, check to see how much water has collected in each of the plastic bags.
  • Which bag has more water collected in it?