18.2 Adaptive features
- Syllabus
- 0610–2026–2027
- Topic
- 18.2
- Level
- —
Learning objectives
18.2.1Adaptive feature as an inherited• Describe an adaptive feature as an inherited feature that helps an organism to survive and reproduce in its environment18.2.2Interpret images or other information• Interpret images or other information about a species to describe its adaptive features18.2.3Adaptive features of hydrophytes• Explain the adaptive features of hydrophytes and xerophytes to their environments
Define an adaptive feature by fitness
An adaptive feature is an inherited feature that helps an organism survive and reproduce in its environment.
A feature increases fitness only if it improves the probability of survival and reproduction under the conditions of that environment. For example, camouflage can reduce detection by predators or prey, increasing the chance of surviving to reproduce.
A useful change acquired during an individual's lifetime is not automatically an adaptive feature: the feature must be inherited and linked to survival and reproduction in the environment.
Explain adaptive features from evidence
Interpret an image or description in three linked moves: 1. state the feature you can actually observe; 2. explain the physical or biological function it could provide; 3. connect that function to survival and reproduction in the stated environment.
Observed feature: a cheetah has a streamlined body. Function: reduced air resistance helps it run quickly. Environmental advantage: catching prey improves its chance of surviving and reproducing.
Do not name a hidden feature that the image does not show, and do not stop at appearance. The explanation must connect evidence to a functional advantage in the given habitat.
Explain hydrophyte and xerophyte adaptations
Hydrophytes live in water, where support and water supply are abundant but gas exchange may be limited by submergence. Xerophytes live where water is scarce, so they must obtain water and reduce loss by transpiration.
| Plant and feature | Mechanism and environmental advantage |
|---|---|
| hydrophyte: large air spaces | lower density for buoyancy and provide internal routes for gas diffusion |
| floating hydrophyte: stomata on upper surface | exposes stomata to air for gas exchange |
| hydrophyte: thin or absent cuticle | little need to prevent water loss; allows easier exchange |
| submerged hydrophyte: narrow or divided leaves | reduces resistance to water flow |
| hydrophyte: reduced roots, xylem and support tissue | water surrounds the plant and provides support |
| xerophyte: thick waxy cuticle | reduces evaporation from the leaf surface |
| xerophyte: small, rolled or spine-like leaves | reduces exposed surface area and traps humid air |
| xerophyte: hairs and sunken or fewer stomata | traps still humid air and reduces the water-vapour gradient or diffusion |
| xerophyte: deep or widespread roots | reaches deep water or rapidly absorbs water over a wide area after rain |
| xerophyte: succulent stem or leaves | stores water for dry periods |
State the mechanism for the observed plant: not every hydrophyte floats and not every xerophyte has every listed feature. A feature is adaptive only when its effect matches the habitat.