Living things is a huge group and is equal to life on Earth.
Living things are normally divided into very broad groups called kingdoms, of which the ones we mostly think of are plants and animals.
The smallest living thing is called an organism. Organisms are composed of one, or more, cells, and can grow, reproduce and, through evolution, adapt to their environment. All living things, no matter how different they seem, are based on cells that live in water. Our bodies are full of water, just as the leaves of plants are.
The earliest life on Earth existed at least 3.5 billion years ago, and we can still find fossil algae (small green plant-like organisms) in Western Australia.
Since emerging, life has evolved into a variety of forms, which biologists have classified as you can see in the diagram.
The group we are used to dealing with is a species - a group of living things that can breed together. The video show a ground squirrel. This ground squirrel is a species.
