Each xerophyte feature solves a stage of the water problem: reduce loss, store water or gain water. Write the feature, the problem it addresses and how it solves it.
This lesson is part of plant adaptations in SPM Biology. Transpiration is covered in transport in plants.
What is the sentence frame?
Use: “The plant has [feature], which [does what], so [effect on water].” Every adaptation answer can follow the same frame.
| Feature | How it helps |
|---|---|
| Thick waxy cuticle | Reduces evaporation from the leaf surface |
| Reduced or spiny leaves | Reduces surface area for transpiration |
| Sunken stomata | Traps humid air, reducing the diffusion gradient |
| Rolled leaves or hairs | Trap humid air near the stomata |
| Fleshy stem or leaves | Stores water |
| Deep or widespread roots | Increase water uptake |
Worked example: a cactus-like plant
An original description: a plant lives in a dry area. It has a thick waxy layer on the stem, leaves reduced to spines and a fleshy stem.
Reduce loss. The waxy cuticle is waterproof, so water cannot evaporate through the surface. The spines have a small surface area, so less water is lost by transpiration.
Store water. The fleshy stem stores water, so the plant can survive long dry periods.
Linking each feature to its effect makes a much stronger answer than a list.
The mistake that loses the reason mark
A student writes: “The xerophyte has a thick cuticle, small leaves and deep roots.” That is a list. It names features but says nothing about why they help.
The improved answer: “A thick cuticle reduces evaporation. Small leaves reduce the surface area for transpiration. Deep roots reach water far below the surface.”
How do I handle a feature I have not seen?
Ask what it does to water: does it reduce the gradient, reduce the surface, block evaporation or store water? For example, hairs on the leaf trap a layer of humid air next to the stomata, so the water vapour gradient is reduced.
A self-check question
A plant in a dry region has its stomata at the bottom of deep pits on the lower surface of rolled leaves. Explain how this reduces water loss.
Answer
The pits and the rolled leaf trap a humid layer of air around the stomata. This reduces the difference in water vapour concentration between the inside of the leaf and the air outside. Less water vapour diffuses out, so less water is lost by transpiration.
Next, see the opposite problem in explaining hydrophyte adaptations. The biological data interpretation trainer offers further practice.
If the explanation step still slips, SPM Biology one-to-one tuition lets a teacher drill the pattern on fresh plants.