Organisms and Classification
The classification system
Classification groups organisms by shared features. Know the main groups: animals (vertebrates and invertebrates), plants, fungi, protoctists and bacteria. Vertebrates divide into fish, amphibians, reptiles, birds and mammals; learn one distinguishing feature of each, such as feathers for birds, mammary glands for mammals, moist skin for amphibians. A frequent trap is calling a whale a fish or a bat a bird; classification uses features, not habitat or movement.
Naming and keys
Binomial naming uses genus and species, with the genus capitalised and both words italicised or underlined. Dichotomous keys use pairs of contrasting statements to identify organisms. When using a key, always start at the first pair and follow one statement at a time; a common trap is skipping steps.
Adaptations
Organisms show adaptations to their environment: structural (shape, colour), behavioural (migration, hibernation) and physiological (sweating, enzyme changes). Questions often ask you to explain how an adaptation helps survival, so link the feature to a benefit.
Worked example
A student finds an organism with feathers and a beak. The key asks: feathers present? yes; then warm-blooded with beak? yes; the organism is a bird. Rule of thumb: follow the key strictly, one decision at a time.
Practical trap
When constructing a key, use observable features and make the two statements clearly opposite.