An arctic fox, a cactus and a water lily each look the way they do for a reason. Their inherited features help them survive and reproduce where they live. Reading an organism's features from a picture or a description is a skill the exam tests often; the detailed adaptations of xerophytes and hydrophytes are Extended content.
An adaptive feature is an inherited feature that helps an organism to survive and reproduce in its environment. To describe one, name the feature and link it to a problem in the habitat: cold, drought, predators, too much water. Extended: xerophytes are plants adapted to dry places and reduce water loss; hydrophytes are plants adapted to living in water.
Start with the arctic fox in the sim. Click each feature, or its chip, and read why it helps in a cold, snowy habitat. Then try the plants.
Always link the feature to the environment. "It has thick fur" earns nothing on its own; "thick fur traps air, which insulates the fox against the cold" is an explanation.
Four quick checks. Each correct answer earns XP and records this skill on your profile.
In the sim, why does the arctic fox have small ears?
What two jobs does the thick white fur of the arctic fox do?
Which description fits an adaptive feature?
In the sim the fox's layer of fat is highlighted. Besides insulation, what does it do?
Exam questions often show a picture or table about an unfamiliar species and ask you to describe its adaptive features. Use the same method every time.
| Step | Ask yourself | Example: camel |
|---|---|---|
| 1 | What is the habitat like? | hot, dry, sandy desert |
| 2 | What feature is shown? | wide, flat feet |
| 3 | What problem does it solve? | spread the weight so it does not sink into soft sand |
| 4 | How does that help survival or reproduction? | it can walk long distances to find food and water |
Extended. Switch the sim to the cactus, marram grass and water lily. Xerophytes live where water is scarce, so their features cut water loss by transpiration or store water. Hydrophytes live in water, where the problems are getting light and exchanging gases, not saving water.
| Plant | Feature | How it helps |
|---|---|---|
| Cactus (xerophyte) | leaves reduced to spines | tiny surface area for water loss; protect the stem from animals |
| Cactus | thick waxy cuticle; few, sunken stomata | less evaporation and less water vapour diffusing out |
| Cactus | swollen green stem; wide shallow roots and a deep root | stores water and photosynthesises; absorbs rain quickly and reaches deep water |
| Marram grass (xerophyte) | leaf rolls up, hairs inside, sunken stomata on the inner surface | traps humid air, reducing the diffusion gradient for water vapour |
| Water lily (hydrophyte) | large, flat floating leaves | absorb as much light as possible |
| Water lily | stomata on the upper surface | in contact with the air for gas exchange |
| Water lily | large air spaces in stems and leaves | keep leaves afloat and let oxygen reach submerged parts |
| Water lily | long, flexible stems; little xylem | bend with water currents; water supports the plant |
Sunken stomata and hairs do not stop water loss completely. They trap moist air, so the concentration gradient of water vapour is smaller and the rate of diffusion out of the leaf is lower.
Unlocks once the four checks above are done. Worth more XP, written to IGCSE Paper 2 and Paper 4 standard.
Extended: which feature would you expect in a xerophyte?
Extended: why are the stomata of a water lily on the upper surface of the leaf?
Extended: marram grass rolls its leaves in dry, windy weather. This reduces water loss mainly because:
A desert mammal has very large ears with many blood vessels near the surface. The best explanation is:
This skill is now recorded on your profile. Keep the chain going.