Xerophyte

In the syllabus and the exam

Xerophyte is one of three habitat-based plant categories tested alongside hydrophyte and mesophyte, and questions typically give a labelled diagram or a described plant and ask candidates to identify it as a xerophyte before explaining how at least two or three named features reduce water loss or maximise water storage and uptake. Commonly cited xerophytic features include a thick waxy cuticle, sunken stomata (often in pits, sometimes covered by hairs that trap moist air), reduced leaf surface area (leaves modified into spines, as in a cactus), a thick fleshy stem or leaf for water storage, and an extensive or deep root system for reaching underground water. Full marks require pairing each feature with its specific effect, for example 'sunken stomata trap a layer of moist air around the pore, lowering the water vapour concentration gradient and so reducing the rate of transpiration', rather than the incomplete statement that sunken stomata simply 'reduce water loss'. A common error is listing a feature that actually belongs to a hydrophyte, such as large air spaces for buoyancy, or naming a feature without stating the mechanism by which it conserves water. Candidates should also be able to compare a xerophyte with a mesophyte of the same general plant type, explaining why the desert plant needs additional features that an ordinary garden plant, growing where water is not limited, does not. Candidates should further note that some xerophytes also fold or roll their leaves during the driest part of the day, temporarily reducing the leaf surface area exposed to the drying effect of moving air.

Example

A cactus stores water in its thick, fleshy stem and has spines instead of broad leaves, two xerophytic features that together cut the surface area available for water loss by transpiration.

Related terms

AdaptationHydrophyteStoma

Source:SRC-DSKP-EN