Transpiration

Plants evaporate great amounts of water – is that what the stomata are for?

Not really. Plants have their stomata to take up the CO₂ they need for photosynthesis. At the same time they lose water from the plant body. The technical term for this kind of water loss is transpiration. The stomata consist of specialized cells, two of which are able to change their shape.

And that’s how they open and close?

Yes. They close the stomata when it is not possible to do photosynthesis or when the plant faces a water deficit. When the stomata are closed, the cuticle – a protective film on top of the leaf – ensures that hardly any water is lost at all. At the same time, no CO₂ is allowed into the plant.

So the stomata help the plant to keep a balance between necessary photosynthesis and non-avoidable transpiration.

Yes, between starving and dying of thirst, so to speak.