Cambridge O Level Biology · Syllabus 5090 · Transport in Flowering Plants
Transpiration Rate
What is Transpiration Rate?
The volume or mass of water vapour lost from a plant's leaves in a given time. It rises when the water-vapour concentration gradient between the leaf air spaces and the atmosphere becomes steeper, as it does in moving air or in dry air; when evaporation from the mesophyll surfaces becomes faster, as it does at higher temperature; and when the stomata are open, as they usually are in the light. It falls in humid air, in still air and in darkness, and it can also fall in extreme heat or drought, when the stomata close to conserve water.
This definition is part of the Transport in Flowering Plants chapter in Cambridge O Level Biology.
Last reviewed Syllabus 2026-2028