This definitions covers Key Definitions within Transpiration for GCSE Biology. Transpiration process, stomatal control, factors affecting rate, plant adaptations, measuring transpiration, and practical investigations It is section 14 of 21 in this topic. Make sure you can use the exact wording confidently, because definition marks are often lost through vague language.
Key Definitions
Transpiration: The evaporation of water from the surfaces of mesophyll cells inside the leaf, followed by diffusion of water vapour through air spaces and out via open stomata into the surrounding air.
Transpiration stream: The continuous movement of water through a plant — from soil, through root hair cells by osmosis, across the root cortex, up through xylem vessels, and out through stomata via transpiration.
Stomata (singular: stoma): Pores in the leaf epidermis through which gas exchange and water vapour loss occur. Opened and closed by guard cells.
Guard cells: Pairs of kidney-shaped cells flanking each stoma. Changes in their turgor pressure (controlled by potassium ion movement) open and close the stomatal pore.
Potometer: An apparatus used to measure the rate of water uptake by a cut plant shoot. It measures water uptake, which is approximately equal to (but not identical to) the transpiration rate.
Xerophyte: A plant adapted to survive in an environment with very little water, such as a desert. Xerophytes typically have structural and physiological adaptations to reduce the rate of transpiration.
Wilting: Loss of rigidity (turgor) in plant cells when the rate of transpiration exceeds the rate of water uptake from the soil, causing cells to become flaccid.
Practice questions for Transpiration
What is transpiration?
Describe the three stages of transpiration in a leaf.
Quick recall flashcards
What is a xerophyte?
A plant adapted to survive in dry/arid conditions with limited water availability (e.g., cacti, marram grass).
What is a potometer?
An apparatus that measures the rate of water uptake by a plant shoot. Used to estimate transpiration rate (though actually measures uptake, not loss).