6.14B Explain how plants are adapted to survive in extreme environments…

The idea

Plants in extreme environments face too much water loss, intense light, heat, cold or shortage of water. Adaptations reduce transpiration and protect the plant. Small, narrow or rolled leaves reduce surface area exposed to sun and wind, so less water evaporates. A thick waxy cuticle on the leaf surface is waterproof and limits evaporation through the epidermis. Fewer, sunken or hairy stomata trap moist air and slow diffusion of water vapour out of the leaf. Each feature must be linked to its effect: for example, a rolled leaf with stomata on the inside keeps humid air around the stomata, lowering the water potential gradient and reducing transpiration. Answers should name the adaptation, describe its structure and explain the mechanism by which it helps survival.

What earns the marks

• Small or narrow leaves reduce the surface area for evaporation, lowering water loss in dry or windy habitats.
• A thick waxy cuticle is waterproof and reduces evaporation of water through the leaf epidermis.
• Fewer stomata, or stomata sunken in pits or covered by hairs, trap moist air and reduce the diffusion gradient for water vapour leaving the leaf.
• Rolled leaves enclose the stomata on the inner surface, keeping humid air close to them and cutting transpiration.
• Each adaptation must be explained by linking its structure to reduced water loss and therefore improved survival in the extreme environment.

Common mistakes and how to put them right

• Listing adaptations without explaining them.

  Put it right: State the mechanism, for example that a thick cuticle is waterproof and so limits evaporation.

• Claiming small leaves increase photosynthesis directly.

  Put it right: Their main benefit is reducing surface area and so water loss.

• Saying stomata 'close permanently' as the only adaptation.

  Put it right: Describe structural features such as sunken stomata and hairs that reduce water loss.

Exam tips

• Use the pattern 'adaptation → structure → effect on water loss → survival benefit' for each point.
• Name the specific leaf feature (cuticle, stomata, leaf size or shape) rather than writing 'special leaves'.
• Link every explanation back to the extreme condition, such as drought, heat or strong wind.