AS Biology: Plants: Xerophytes

Plants in different habitats have different adaptations:

• Mesophytes: plants adapted to a habitate with adequate water
• XEROPHYTES: plants adapted to dry habitat
• Halophytes: plants adapted to a salty habitat
• Hydrophytes: plants adapted to a freshwater habitat

XEROPHYTES ADAPTATIONS

• Thick cuticle - stops uncontrolled evaporation though leaf cells
• Small leaf surface area - less surface area for evaporation and transpiration
• Low stomata density - smaller surface area for diffusion
• Sunken stomata, stomatal hairs, rolled leaves - maintains humid air around stomata e.g. marram grass
• Extensive root - maximise water uptake
• Spines - protect from animals

Sunken stomata - creates a local humidity, decreases exposure to air currents; moist air is trapped here in the diffusion pathway and reduces evaporation rate

Rolled leaves: traps moist air so reducing transpiration. Plus, smaller surface area of lead is exposed to the drying effects of the wind.

Stomata on inside of the rolled leaf creates local humidity/decreases exposure to air currents because water vapour evaporates into air space rather than atmosphere. e.g. marram grass Fewer stomata decreases transpiration as this is where water is lost.

Marram grass

Marram grass possesses:

Rolled leaves leaf hair and sunken stomata. These adaptation make it resistant to dry conditions and of course sand dunes which drain very quickly and retain very little water.

OCR, June 03, Q3.

Some plants, such as cacti, inhabit dry areas. These plants of dry areas are known as xerophytes. Reduction of water loss by the process of transpiration/evaporation can be achieved by employing a variety of adaptations. In some species the leaves are needle-like, which reduces the surface area to volume ratio, whilst in others the epidermis is covered by a thick layer of waxy cuticle. In order to conserve the greatest amount of water, many species shut their stomata during the day,