Classification · Grade 4
There are millions of different kinds of living things. To make sense of them, scientists sort them into groups by the features they share: this is classification. Animals with a backbone are vertebrates, those without are invertebrates, and every living thing belongs to a kingdom and has a two-part scientific name. Keys help us identify an organism step by step.
Key facts
- Vertebrates have a backbone. There are five groups: fish (scales, gills, fins), amphibians (moist skin, lay eggs in water), reptiles (dry scaly skin, lay leathery eggs on land), birds (feathers, beaks, hard-shelled eggs) and mammals (hair or fur, feed their young on milk).
- Invertebrates have no backbone: insects (6 legs, 3 body parts), arachnids such as spiders (8 legs, 2 body parts), crustaceans (hard shell, many legs), molluscs (soft body, often a shell), worms and jellyfish.
- Carl Linnaeus sorted living things into groups inside groups: kingdom, phylum, class, order, family, genus, species.
- Five kingdoms: animals, plants, fungi, protists (single-celled organisms with a nucleus) and prokaryotes (bacteria).
- Every species has a two-part (binomial) name: the genus, then the species, written in italics. Humans are Homo sapiens; the lion is Panthera leo and the tiger Panthera tigris.
- Two species in the same genus are closely related. Scientists now also group life into three domains, using chemical analysis of cells: Archaea, Bacteria and Eukaryota.
- A key is a set of questions, each with two answers, that leads you to the name of an organism.