What is transpiration?
Quick answer
Transpiration is the process by which plants release water vapor into the air, mostly through tiny pores in their leaves called stomata. It pulls water up from the roots, keeps plants cool, and moves nutrients. Most of the water a plant absorbs, often more than 90%, is lost this way.
Plants don’t sweat, but they do something very similar, and it keeps water moving through every forest, field and houseplant on Earth.
How transpiration works
- Roots absorb water from the soil.
- Water travels up through tubes called xylem, like straws inside the stem.
- In the leaves, water evaporates into air spaces.
- Water vapor escapes through stomata, mainly on the underside of leaves.
- As water leaves, it pulls more water up behind it, a force called the transpiration pull.
This can lift water to the top of trees over 100 meters tall, without any pump.
What are stomata?
Stomata are microscopic openings surrounded by guard cells that open and close. They let in carbon dioxide for photosynthesis, but also let water out. On hot, dry days, plants close them to save water, which is why wilting plants grow more slowly.
What speeds it up?
| Factor | Effect on transpiration |
|---|---|
| Heat | Increases it |
| Wind | Increases it, by carrying moist air away |
| Low humidity | Increases it |
| Bright light | Increases it, as stomata open for photosynthesis |
| Dry soil | Decreases it, as stomata close |
Why it matters
- Cooling: Like sweating, evaporation keeps leaves from overheating.
- Nutrients: Water carries minerals from the soil to every part of the plant.
- Rain: Transpiration returns huge amounts of water to the air. Forests like the Amazon help create their own rainfall.
A large tree can release hundreds of liters of water on a hot summer day.
Transpiration vs evaporation
Evaporation is water turning to vapor from any surface, like a puddle. Transpiration is evaporation through living plants. Together, scientists call them evapotranspiration.
Why leaves change color and fall when transpiration slows in autumn: why leaves change color. Growing plants at home? See how to grow herbs.
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