There are millions of kinds of living things — so scientists sort them into groups by the features they share. Today you'll learn how, then you will predict each creature's group.
Before we start — you sort things every day — toys, animals, foods. What features do you use to decide what goes together?
With millions of living things, we group them by features they share — it makes them far easier to study and name. We look at clues like: does it have a backbone? does it have fur, feathers, or scales? how does it get its food?
The broadest groups are kingdoms, told apart by how a thing is built and how it gets food: Plants make their own by photosynthesis · Animals eat other living things · Fungi absorb food from dead matter · Protists are mostly tiny single cells (amoebas, algae) · Bacteria are even tinier single cells with no nucleus.
Animals split in two. Vertebrates have a backbone (a spine). The vast majority — about 97% — are invertebrates with no backbone: insects, spiders, worms, snails. A quick clue among them: insects have 6 legs and 3 body parts; arachnids (spiders) have 8 legs and 2 body parts.
The backboned animals fall into five groups, told apart by skin, breathing, eggs, and body heat: Mammals (fur, feed milk, warm-blooded) · Birds (feathers, lay eggs, warm-blooded) · Reptiles (dry scales, eggs on land, cold-blooded) · Amphibians (moist skin, start in water then land, cold-blooded) · Fish (wet scales, gills, fins, cold-blooded).