Sorting and Classifying Living Things
≈ 20 minThere are millions of species, so scientists classify them: they sort organisms into groups whose members share observable features. Classification makes life findable — and it lets you predict things about an organism you have never seen before, just from the group it belongs to.
The broadest everyday groups are:
| Group | Makes its own food? | Moves about? | Example |
|---|---|---|---|
| Plants | yes, using sunlight | no | protea, maize |
| Animals | no — eats other organisms | yes | eland, hadeda, dung beetle |
| Fungi | no — absorbs food from dead or living matter | no | mushroom, bread mould |
Animals are split first into invertebrates (no backbone: insects, spiders, worms, snails) and vertebrates (with a backbone). Vertebrates are then sorted into five groups:
- fish — live in water, breathe with gills, scales;
- amphibians — moist skin, young live in water (platanna, rain frog);
- reptiles — dry scaly skin, eggs with leathery shells (tortoise, puff adder);
- birds — feathers, beaks, hard-shelled eggs;
- mammals — hair or fur, feed their young on milk.
Worked example — using a two-way key. A key asks yes/no questions that split a group in half each time.
- Does it have a backbone? No → invertebrate. Yes → go to 2.
- Does it have feathers? Yes → bird. No → go to 3.
- Does it feed its young on milk? Yes → mammal. No → go to 4.
A hadeda answers "yes" at question 2 and is identified as a bird in two questions.
A mushroom is growing on a dead log. It has no leaves, cannot make its own food, and takes in nutrients from the rotting wood. Which group does it belong to?
What is the general name for animals that have a backbone?
A learner collects 24 small animals from a school garden. She finds that 18 of them have no backbone. How many of the 24 are vertebrates?
Many learners call a whale a fish. Which piece of evidence shows most clearly that a whale is a mammal?