Investigating the effect of increasing temperatures on transpiration

Transpiration is the loss of water from a plant. Transpiration mainly occurs from the leaves. Water vapour diffuses out of the stomata ( tiny pores mostly found on leaves ).

Loss of water from the leaves creates a pull on the water in the xylem cells, drawing water up the plant. This movement of water from roots to leaves is called the transpiration stream.

Xylem cells form a continuous tube from the leaves of a plant to the roots, a bit like a drinking straw providing a continuous flow of water.

The transpiration stream transports minerals and water around the plant and keeps cells turgid ( full of water ) so they can support the plant without it wilting.

Rate of Transpiration Experiment

How does increasing temperature and airflow around a plant affect the transpiration rate?

This simple investigation uses a hairdryer to increase the airflow and temperature around the leaves of a celery stick to find out how the transpiration rate is affected.

You’ll need

Two celery stalks with leaves

Food colouring

Water

A hairdryer

Ruler

Instructions

Choose two stalks of celery with leaves that are similar in size.

Cut them to the same length.

Place each stalk in a container of water and food colouring. Make sure the same amount of water and food colouring is used for each sample.

Celery in coloured water for a transpiration investigation

For half an hour, blow warm air from a hairdryer over the leaves of one celery stalk every 5 minutes.

After half an hour, remove the celery stalks from the water and carefully slice them to see how far up the coloured water has reached.

celery stalk cut in half to show how far water coloured with food colouring has reached up the stalk. — Celery stalk exposed to heat from a hairdryer – notice the wilted leaves.

Celery cut to see how far up the stalk food colouring and water has reached in a transpiration investigation — Celery stalk not exposed to heat from a hairdryer

food colouring and water that has travelled up a celery stalk. The blue food colouring can be clearly seen in the celery

How does increasing airflow and temperature affect the rate of transpiration

We found that the celery sample exposed to heat from the hairdryer had a much faster rate of transpiration than the celery that was not exposed to heat.

The coloured water had travelled much further up the stalk of the sample exposed to heat than the one not.

How the movement of air affects transpiration

Air flow removes water vapour from around a leaf, creating a concentration gradient ( low concentration of water in the air and high concentration in the leaf ) between the leaf and air, increasing water loss from the leaf. If there’s not much airflow, the water vapour doesn’t move far from the leaf, so there’s a high concentration of water inside and outside of the leaf and so no concentration gradient for diffusion.

How temperature affects transpiration

Higher temperatures mean water molecules evaporate at a faster rate which increases the rate of transpiration.

What else affects the rate of transpiration

The amount of light also affects the transpiration rate. Stomata close in the dark so water cannot diffuse out.

More experiments to investigate transpiration

These colourful flowers look much more impressive than the celery, but the process is the same!

white carnations with colourful petals thanks to transpiration.

Water is transported up the stem of a plant by a process called capillary action. You can try this out by placing paper flowers into a tray of water and watching them open up.