Explain the Role of the Stomata in Gas Exchange in Plants

What did the plant say to its stem? 

​I'd never leaf you! 

Now all jokes aside, plants rely on their leaves for survival. Plants use sunlight to make glucose - this process is called photosynthesis.

Plants have different structures that help them to make glucose.

One of the main structures is the leaf. A leaf has many adaptations that allow it to carry out photosynthesis effectively. Let's look at these in more detail below:

The leaf is quite a complicated organ when looked at under a microscope, as you can see from the picture above! 

In order to photosynthesise, plants need carbon dioxide and water. These reactants are essential to make glucose. They also release oxygen which is essential for us to stay alive!

So how do plants get this carbon dioxide and water?

On the underside of the leaf are small holes or pores called stomata. These pores (stoma for one pore) allow carbon dioxide to enter from the environment.

Stomata have guard cells on either side of them, to control their size. If the guard cells swell up the stomata will become smaller or close completely. If the guard cells shrink the opposite happens -  the stomata open.

Stomata are open during the day and closed at night. Why might that be?

Well, at night there's no sunlight, so plants can't photosynthesise, so there's no need for the stomata to be open. During the day, the carbon dioxide is able to enter the leaf to be used for photosynthesis.

When the stomata open to allow carbon dioxide in, water vapour from the plant escapes. It's a bit like opening the front door on a very cold day to let a guest in - in doing so the heat from your house escapes - it can't be helped! Having the stomata closed at night prevents further water loss. Remember that the plant needs water for photosynthesis, so it wants to hold onto it as much as possible!

In the following activity, we will look at the role of the stomata in gas exchange.