Factors affecting water uptake

Plant structures and their functions · Leaves, water uptake and extreme environments · note 2 of 4

Spec 6.12Download these notes (PDF)5 pages

Factors affecting water uptakeSpec 6.12

The rate at which a plant takes up water depends on the rate of transpiration. When more water is lost from the leaves, more is pulled up through the xylem. Three environmental factors affect it.

Effect of environmental factors on water uptake
Factor	Effect on water uptake	Explanation
Light intensity	Higher light intensity increases the rate	Stomata open in the light, so more water vapour can diffuse out of the leaf. Low light or darkness makes the stomata close.
Air movement	More air movement increases the rate	Moving air carries away water vapour from around the stomata. This keeps a steep concentration gradient, so water vapour diffuses out faster.
Temperature	Higher temperature increases the rate	Water evaporates from the cells faster, and water vapour particles move faster, so diffusion out of the leaf is faster.

A potometer is used to measure 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 moved in a set time is a measure of the rate. You can compare the rate in different conditions, for example with and without a fan, or in the light and in the shade.

A potometer: a leafy shoot sealed with an airtight seal into a water-filled tube, a water reservoir with a tap, and a capillary tube over a ruler with an air bubble that moves towards the shoot; the end of the capillary dips into a beaker of water. — A potometer: the **distance the bubble moves** in a set time measures the rate of water uptake.