Pastel clay models of many living things lined up on a shelf, including mushrooms, a fern, coral shapes and various round forms
Body 101 · Lesson 7 · ages 8 to 13

The wall of life, every living thing is a relative

About two million kinds of living thing on Earth have been given names, and scientists think several million more are still waiting to be found. All of them, from the bacteria in a ditch to a great tree and to you, use the very same genetic code. That means every living thing on Earth shares a common ancestor. This lesson walks along the whole wall of life, one group at a time.

A pink desk with stacked books, a slide, and a conical flask of green liquid
1 · The map3 domains

The tree of life

People once split living things into plants and animals and nothing else. Then microscopes arrived, and later the reading of genetic code, and the truth turned out to be far richer. Today we use 3 great domains. Tap a box to see more.

The common ancestor of all life Bacteria Archaea Eukaryotes Protists Fungi Plants Animals Cells with no nucleuscalled prokaryotesCells with a nucleus, called eukaryotes
A surprise that changed the pictureArchaea look very much like bacteria, but reading their genetic code showed they are actually closer to us, the eukaryotes, than they are to bacteria. It is a good example of how grouping things by eye alone can lead you astray.
Several pastel petri dishes on a pink table, the middle one holding a pale green spiral pattern
2 · BacteriaThe most numerous on Earth

Bacteria, single cells that live everywhere

One teaspoon of soil holds more bacteria than there are people on Earth. Your own body carries about as many bacterial cells as it has cells of its own. Most do us no harm at all, and many are necessary for our lives. Tap to see each kind.

A small model of a hot spring with turquoise water, ringed by orange rock and little trees
3 · ArchaeaSurvivors in extreme places

Archaea, the group that was split off recently

Until 1977 people still thought of these as odd bacteria. Then a scientist called Carl Woese compared their genetic code and found they were a completely separate line. Many live in places where nothing else can.

Three clay water droplets, hollow and pale blue inside, on a pink surface
4 · ProtistsThe group holding everything else

Protists, a world in a drop of water

Protists are the eukaryotes that are not plants, not animals and not fungi. Most are single cells, but with a full nucleus. They are so varied that scientists say this is not really one group at all, but a collection of lines that have not been sorted out yet.

Half the planet's breath Phytoplankton in the sea, most of them protists, make about half of all the oxygen we breathe. The Amazon matters enormously, and so does the ocean.
Pink and white clay mushrooms growing on a log covered in green moss
5 · FungiCloser to animals than to plants

Mushrooms, moulds and yeasts

Fungi are not plants. They have no chlorophyll and cannot photosynthesise, so they digest food outside themselves and absorb it. Their cell walls are made of chitin, the same material as an insect's shell. Reading their genetic code showed that fungi are actually closer to animals than to plants.

The mushroom you see is only the tipThe mushroom is only the reproductive part. The real organism is a web of fine threads spread through the ground over a wide area. In Oregon there is a fungus whose threads cover several square kilometres, counted as the largest single living thing in the world.
Three clay pots holding ferns and moss, standing beside an open book
6 · PlantsThe planet's power stations

Plants, from moss to great trees

Every plant makes its own food from sunlight, water and carbon dioxide. But the earliest plants had no transport tubes and no seeds, so they had to stay close to water. In order of evolution, they go like this.

Clay models of a bird, a goldfish and an orange cat on a pink table, with a toy car and a potted plant beside them
7 · AnimalsMost of them have no backbone

Animals, with and without backbones

Every animal eats other living things, moves at least during part of its life, and has cells with no cell wall. What many people do not realise is that over 95 percent of animal species have no backbone, and nearly half of all animals are insects.

8 · The toolThe one biologists really use

A key for identifying living things

Biologists work through yes or no questions, one at a time, to narrow down which group something belongs to. Have a go. Think of any living thing, then answer truthfully.

GameRace the 45-second clock

Which group is it in?

Read the name of the living thing on the card, then pick the right group. A run of right answers earns a bonus.

Press start whenever you are ready
0points 45seconds

A right answer scores 10 points, and a longer run means a bigger bonus.

Review12 questions

Test yourself

Correct: 0 of 12

Fancy a game on this lesson?

Every question from this lesson is in the Body 101 arena. Race the clock, duel someone at home, play as a team, beat the bosses, or practise with no timer at all.

Play this topicThe whole arena