Aseel Samaro

Exploring the role of stomata

Plants are found in a huge range of habitats.

In order to photosynthesise, plants need a supply of carbon dioxide.

How do plants get carbon dioxide? Why does oxygen, a product of photosynthesis, not build up in the leaf?

Introduction

Land plants have pores (holes) on the underneath surface of their leaves.

These pores can open and close to control materials that flow in and out of the leaf.

These special structures are called stomata (the plural of stoma).

When a plant needs carbon dioxide, the stomata open, allowing the gas into the leaf.

Two guard cells, one on either side of each stoma, control the opening and closing of the stoma.

How do plants get the carbon dioxide they need?

Look at this picture. What shape are the guard cells?

What are stomata and where are they found?

Describe how gases pass in and out of a leaf.

What is the name of the cells that control the size of the stomata?

What are stomata and where are they found?Pores; on the underside of leaves

Describe how gases pass in and out of a leaf.Carbon dioxide diffuses into the leaf through the stomata and moves through it in

the air spaces in the spongy mesophyll. Oxygen passes through the air spaces and out of the stomata.

What is the name of the cells that control the size of the stomata?Guard cells; there is one either side of the stoma.

Guard cells have chloroplasts and can photosynthesise.

When the guard cells are full of water, they open the stomata.

As the plant takes in carbon dioxide (CO2) from the air, oxygen (O2), a waste product of photosynthesis, is removed through the stomata.

At the same time, water escapes from the plant.

A stoma cannot stay open because the guard cells shrink back as the water escapes, and so the stoma closes.

Observing stomata

Open and closed stomata

Why must guard cells come in pairs?

Draw an annotated diagram to explain how stomata control the flow of substances in and out of the leaf.

Explain why stomata are found on the underside of leaves.

Why must guard cells come in pairs?To form the hole, and to open and close the stomata.

They fill with water and open the stoma; when the guard cells contain a little water, they close.

Draw an annotated diagram to explain how stomata control the flow of substances in and out of the leaf.

Diagram should show open and closed stomata (as Figure 2.2.5b); labelled similarly explaining water concentrations.

Explain why stomata are found on the underside of leaves.There would be too much evaporation of water; from the leaf if the stomata were on the

upper surface.

Look closely at the photographs of stomata from different plants in the coming figure.

The number of stomata varies depending on environmental factors, such as:

The concentration of carbon dioxideThe humidity of the air.

Density of stomata

Stomata from different plants: one with low stomatal density and one with high stomatal density

Suggest two other environmental factors that will affect the number of stomata

Describe how environmental factors would affect the number of stomata

Suggest two other environmental factors that will affect the number of stomata

Temperature; availability of light

Describe how environmental factors would affect the number of stomata

Example: low carbon dioxide concentration may favour high stomatal density.

Plants respire just as animals do.

They respire all day and all night, but only photosynthesise during the hours of daylight.

Did you know…?

Thank you