7.1.4

Adaptations to Water Availability

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Xerophytic Plants

Xerophytic plants are specialised to dry habitats where water availability is low. The plants have evolved a number of features to prevent water loss.

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Fewer stomata

  • Xerophytic plants have evolved to have fewer stomata to avoid dehydration.
    • The stomata of most plants remain open during the day to allow the exchange of carbon dioxide and oxygen for photosynthesis.
    • Water is also lost through the stomata when they are open. In dry environments, this could dehydrate the plant.
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Sunken stomata

  • The stomata of xerophytes are also sunk into pits in the epidermis.
    • The pits trap moist air. This decreases the water potential gradient between the inside of the leaves and the outside.
    • The lower water potential gradient slows the rate of diffusion of water out of the stomata.
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Hairs

  • Xerophytic plants have fine hairs covering the epidermis.
    • The hairs trap moist air in the same way as the sunken pits.
    • The hairs decrease the rate of water loss.
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Curled leaves

  • The leaves of xerophytes are often curled up so that the stomata are sheltered from the wind.
  • Wind increases the rate of diffusion of water from outside the plant.
    • The curling of the leaves helps reduce the effect of wind and so slows the rate of water loss.
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Cuticle

  • The leaves and stems of xerophytic plants are covered in a waxy cuticle.
    • The cuticle is waterproof and so reduces the rate of evaporation of water.

Jump to other topics

1Cell Structure

2Biological Molecules

3Enzymes

4Cell Membranes & Transport

5The Mitotic Cell Cycle

6Nucleic Acids & Protein Synthesis

7Transport in Plants

8Transport in Mammals

9Gas Exchange

10Infectious Diseases

11Immunity

12Energy & Respiration (A2 Only)

13Photosynthesis (A2 Only)

14Homeostasis (A2 Only)

15Control & Coordination (A2 Only)

16Inherited Change (A2 Only)

17Selection & Evolution (A2 Only)

18Classification & Conservation (A2 Only)

19Genetic Technology (A2 Only)

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