Summary
Evaporation of water from leaves that pulls water up the plant through the xylem.
In depth
About 99 percent of water taken up is lost. Rate increases with light, temperature, wind and low humidity; it is measured with a potometer. Transpiration cools leaves and drives mineral transport.
Water vapour diffuses from the moist leaf interior through stomata to drier air. Factors: humidity gradient, wind removes the boundary layer, and temperature. Plants balance water loss and CO2 gain.
Example: a potometer measures water uptake as a proxy for transpiration.
Transpiration pulls water and minerals, cools leaves (latent heat) and keeps turgor. A large oak tree can transpire hundreds of litres a day. Factors include stomatal opening, leaf area, humidity, wind, light and temperature. Xerophytes reduce loss with thick cuticles, sunken stomata, hairs, rolled leaves (marram grass) and reduced leaves.
A potometer measures water uptake (an approximation of transpiration), and weight loss or cobalt chloride paper can be used. Plants face a trade-off: opening stomata for CO2 means losing water, and for each CO2 gained, hundreds of water molecules may be lost in C3 plants.
Example: guttation, water droplets at leaf edges at night, results from root pressure when transpiration is low.
Frequently asked questions
What is Transpiration?
Evaporation of water from leaves that pulls water up the plant through the xylem.
Which area of biology covers Transpiration, and how advanced is it?
Transpiration is one of the 56 topics in Plant Biology. It is rated Intermediate, so it suits learners who already know the core vocabulary. Related topics in this area include Stomata, Leaves, Cohesion-Tension Theory.
Can you give an example of Transpiration?
A large tree can transpire hundreds of litres a day.
What should I learn before Transpiration?
Work through the Beginner topics in Plant Biology first, such as Plant Kingdom, Photosynthesis, Chlorophyll, then return to Transpiration. Intermediate topics assume the Beginner vocabulary.
What topics are related to Transpiration?
The closest topics to Transpiration are Stomata, Leaves, Cohesion-Tension Theory, Plant Water Potential. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Transpiration?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Transpiration. To practise the whole of Plant Biology, use the Plant Biology quiz.
How is Transpiration different from Stomata?
Transpiration: Evaporation of water from leaves that pulls water up the plant through the xylem. Stomata: Pores on leaves flanked by guard cells that open and close to regulate gas exchange and water loss. Read both side by side and note what each one explains.
How should I study Transpiration step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Stomata and explain the difference aloud. Finally, take the Plant Biology quiz and come back to this page for any question you miss.