Transpiration

Transpiration is the loss of water vapour from the aerial parts of a plant, predominantly through the stomata of the leaves. While transpiration is an inevitable consequence of gas exchange, it plays a vital role in driving the movement of water through the plant. This lesson covers the factors that affect transpiration rate, the potometer practical, guard cell function and xerophyte adaptations, as required by Edexcel GCSE Biology (1BI0) Topic 6.

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What is Transpiration?

Transpiration is defined as the loss of water vapour from the surfaces of a plant, mainly through the stomata in the leaves.

The Process

1. Water evaporates from the surfaces of mesophyll cells inside the leaf
2. The water vapour collects in the air spaces in the spongy mesophyll
3. The water vapour diffuses out through the open stomata into the surrounding atmosphere
4. This diffusion occurs because the air inside the leaf is usually more humid (higher concentration of water vapour) than the air outside