The Earth holds countless living things that differ in shape and way of life, so grouping them by what they have in common is the only way to see them clearly.
The largest groups are kingdoms, and one common scheme uses five: bacteria (prokaryotes), protists, fungi, plants and animals.
Going down from kingdom to phylum, class, order, family, genus and species, each group gets narrower and its members look more alike.
Vertebrates are further split into fish, amphibians, reptiles, birds and mammals, and comparing how they breathe and how they control body temperature makes the differences clear.
How are living things classified?
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The five kingdoms that divide living things into five large groups, with examples of each
💡 Features of the five kingdoms
①Animals move by themselves and get food by eating other living things.
②Plants make their own food by photosynthesis.
③Fungi, such as mushrooms and moulds, reproduce by spores and break down dead matter.
④Protists are single-celled or simply built organisms whose cells have a nucleus, such as amoebas and paramecia.
⑤Prokaryotes are single cells without a nucleus; bacteria belong here.
Levels of classification
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The levels of classification narrowing from kingdom to species, using the grey wolf as an example
Levels of classification
kingdom → phylum → class → order → family → genus → species
Towards kingdom the groups are broader; towards species they hold living things that are more alike.
🔍 Reading the levels
①The groups narrow in the order kingdom, phylum, class, order, family, genus, species.
②The animal kingdom holds a huge number of animals, but a species holds only living things that are almost the same.
③A species is a group whose members can mate and produce offspring that can themselves reproduce.
④As the picture shows, the grey wolf belongs in turn to Animalia, Chordata, Mammalia, Carnivora, Canidae and Canis.
Diversity of vertebrates
Five groups of vertebrates
Classifying vertebrates
group
breathing organ
body temperature
examples
fish
gills
varies
goldfish, shark
amphibians
gills → lungs and skin
varies
frog, salamander
reptiles
lungs
varies
snake, turtle
birds
lungs (air sacs)
constant
sparrow, eagle
mammals
lungs
constant
human, whale
🦎 Key facts about vertebrates
①Fish, amphibians and reptiles are ectotherms: their body temperature changes with their surroundings.
②Birds and mammals are endotherms: they keep their body temperature steady.
③Young amphibians breathe with gills in water, and adults breathe with lungs and skin and can live on land.
④Whales live in water but breathe with lungs and feed their young on milk, so they are mammals.
Exam checklist
Key summary
biodiversity = genetic diversity + species diversity + ecosystem diversity
The greater the diversity, the better an ecosystem withstands change.
🎯 Exam points
①The five kingdoms are prokaryotes, protists, fungi, plants and animals.
②The levels are kingdom, phylum, class, order, family, genus and species.
③Whether two organisms are the same species depends on whether they can produce offspring that can reproduce.
④Ectotherms and endotherms differ in how they control body temperature.
⑤Protecting biodiversity keeps ecosystems stable and preserves resources such as food and medicines.
Examples and unit test
Example 1
Among the five kingdoms, which group makes its own food by photosynthesis, and which group reproduces by spores as a decomposer like mushrooms and molds?
1
The five kingdoms are prokaryotes, protists, fungi, plants and animals.
2
The group that makes food by photosynthesis is the plants, and the group that reproduces by spores and acts as decomposers is the fungi.
▸ plants / fungi
The five kingdoms are separated by observable features such as photosynthesis, the presence of a nucleus and the number of cells.
Example 2
In the classification ranks kingdom → phylum → class → order → family → genus → species, which rank is the broadest and which is the narrowest?
1
Towards kingdom the levels are broader; towards species they gather living things that are more alike.
2
So the broadest level is the kingdom and the narrowest is the species.
▸ Broadest = kingdom / narrowest = species
The lower the level, the more alike the living things grouped together.
Unit-test style
Which statement about classifying organisms is correct?
①Plantae gets its food by eating other organisms
②In the ranks, species is a narrower range than kingdom
③Fungi make food by photosynthesis
④Bacteria are made of cells that have a nucleus
⑤In the ranks, species is the broadest range
▸ ② In the ranks, species is a narrower range than kingdom
1
Kingdom is the broadest rank and species the narrowest, so species is a narrower range than kingdom.
2
Plantae makes food by photosynthesis (①), Fungi are decomposers, not photosynthetic (③), bacteria are prokaryotes without a nucleus (④), and kingdom is the broadest rank (⑤).