Adaptations to Water Availability
Biology: Cambridge International A Level, topic 7.1.4
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.
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.
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.
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.
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.
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.
Test yourself on Adaptations to Water Availability
Which of the following statements about xerophytic plants are true?
Which of these are NOT a feature of xerophytic plants to control water loss?