Factors affecting water uptake, and the potometer

Overview

How light, temperature, air movement and humidity change the rate of water uptake, why plants wilt on a hot windy day, and using a potometer to measure and calculate the rate.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   What effect does increasing light intensity have on the rate of water uptake by a plant, and why?

   Model answer

   It increases it, because the stomata open wider in the light so more water vapour escapes.

2. 2

   What effect does raising the temperature have on the rate of water uptake, and why?

   Model answer

   It increases it, because water evaporates from the leaf cells and diffuses away faster when it is warmer.

3. 3

   What effect does air movement have on the rate of water uptake, and why?

   Model answer

   It increases it, because moving air sweeps water vapour away from the leaf and keeps the concentration gradient steep.

4. 4

   What effect does very humid air have on the rate of water uptake, and why?

   Model answer

   It slows it, because the air outside the leaf is already moist so less water vapour diffuses out.

5. 5

   Why does a plant still take up some water in the dark?

   Model answer

   The stomata are not completely sealed, so a little water vapour still escapes, although far more slowly than in the light.

6. 6

   Explain why a plant may wilt on a hot, windy day.

   Model answer

   Water is lost from the leaves faster than the roots can replace it, so the cells lose their turgor and the plant droops.

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