Transpiration: results

The graph clearly shows that the humidity inside the polythene bag is increasing with time. This increase in humidity is due to the transpiration from the plant.

Answers to questions

1. The small pores that are found on the undersides of leaves are called stomates.
2. Transpiration accounts for approximately 10% of all evaporating water.
3. Plants pump the water up from the soil to deliver nutrients to their leaves.
4. Darkness, internal water deficit, and extremes of temperature tend to close stomates and decrease transpiration; illumination, ample water supply, and optimum temperature open stomates and increase transpiration. You could test this by comparing the transpiration from a control leaf to that of similar sized leaves in different environmental conditions.
5. The guard cells control the opening and closing of the stomates in response to various environmental stimuli.

Teachers’ notes

Not all scientists agree on the significance of transpiration. Transpiration was previously thought to provide the energy to move water in the plant and also to cool the plant. Now scientists believe that transpiration is just an unfortunate side-effect of the stomates' main function of absorbing carbon dioxide and expelling oxygen in photosynthesis.

Credits, comments and further info

This experiment was written by Pico Technology.