Classification and variation
Biology · Key Stage 2 · The School
Grouping by real features
Vertebrates (with a backbone) split into mammals, birds, reptiles, amphibians and fish; invertebrates include insects, spiders, molluscs and worms. Classification groups by shared features, not by where an animal lives — a whale is a mammal and a bat is a mammal, however they move.
Branching keys
A key asks yes/no questions that split the group in half each time: "Does it have six legs?" Follow the branches to the name. Building your own key for six classroom objects teaches the logic faster than using one, because you must choose questions with clean, unarguable answers.
Two kinds of difference
Some variation is INHERITED (eye colour, natural hair colour); some is ENVIRONMENTAL (a scar, a suntan, a language you speak); much is both (height depends on genes and on diet). Sorting examples into the three cases is exactly the reasoning genetics needs later.
Eye colour: inherited. A scar: environmental. Blood group: inherited. Being able to speak Urdu: environmental. Natural hair colour: inherited. Height: BOTH — genes set the range, and food and health decide where in it you land. The test to apply: could this feature have been different if the person had lived a different life? If yes, the environment had a hand in it.