Leaves, water uptake and extreme environments — Edexcel GCSE Combined Science
The factors that affect the rate of water uptake and transpiration, measuring it with a potometer, and transpiration rate calculations.
Revision notes
2 short notes, in the order of the specification. Each one in short:
The rate of water uptake by a plant depends on the rate of transpiration, which is increased by higher light intensity, more air movement and higher temperature. Light opens the stomata, moving air carries water vapour away to keep a steep concentration gradient, and warmth makes water evaporate and diffuse faster. A potometer measures the rate.
A rate of transpiration or water uptake is the change in a quantity divided by the time taken, for example the distance a bubble moves in a potometer per minute. Percentage change in mass equals change in mass divided by original mass, times 100. Calculate a mean from repeats first, and always give the unit, such as mm per minute.
Exam questions
4 exam-style questions (13 marks), each with its mark scheme.
Answer the questionsFlashcards
6 cards: flip them, mark what you knew, and practise the rest.
Practise the cardsMind map
The whole of plant structures and their functions on one page, so you can see where this subtopic fits.
Open the mind mapPrint it
Free PDFs to print or save.
Quick check questions
What does a potometer measure?
Show answer
The rate of water uptake of a leafy shoot.
Why does moving air increase the rate of transpiration?
Show answer
It carries away water vapour, keeping a steep concentration gradient so water vapour diffuses out faster.
A bubble in a potometer moves 24 mm in 8 minutes. What is the rate?
Show answer
24 ÷ 8 = 3 mm per minute.
Why does a higher temperature increase the rate of water uptake?
Show answer
Water evaporates from the leaf cells faster and water vapour diffuses out faster, so more water is pulled up the xylem.
Frequently asked questions
How does light intensity affect the rate of transpiration?
A higher light intensity increases the rate of transpiration. The stomata open in the light, so more water vapour can diffuse out of the leaf, and more water is pulled up through the xylem. In low light or darkness the stomata close, so less water vapour is lost and the rate of water uptake falls.
How does a potometer work?
A potometer measures the rate of water uptake of a leafy shoot. As the shoot takes up water, an air bubble moves along a capillary tube. The distance the bubble moves in a set time is a measure of the rate. You can compare conditions, for example with and without a fan, or in the light and in the shade.
Written and checked against the Edexcel GCSE Combined Science (1SC0) specification · Updated October 2026