What is Diversity in Living Things?
All the differences within and between living things — including every species on Earth, from the tiniest bacterium to the largest whale.
Look around you. From the grass in a park to the birds flying overhead, from the mould on old bread to the fish in the ocean — life comes in an astonishing variety of shapes, sizes, and forms. This variety is what we call biodiversity.
Scientists estimate there are millions of different species on Earth. To make sense of this incredible diversity, scientists sort and group living things based on their similarities and differences. This process is called classification.
Think about a library. If every book was placed randomly on shelves, finding what you need would be nearly impossible. By organising books into categories — fiction, science, history — you can find things much more easily. Classification does the same thing for living things!
What Makes Something Alive? The Characteristics of Living Things
Before we can classify living things, we need to ask: what actually makes something alive? Scientists have identified seven key characteristics that all living things share. A helpful way to remember them is the acronym MRS GREN:
A memory aid for the seven characteristics of living things: Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, and Nutrition.
| Letter | Characteristic | What it means |
|---|---|---|
| M | Movement | Organisms move some or all of their parts |
| R | Respiration | Organisms release energy from food |
| S | Sensitivity | Organisms detect and respond to changes in their environment |
| G | Growth | Organisms increase in size and complexity |
| R | Reproduction | Organisms produce offspring |
| E | Excretion | Organisms remove waste products |
| N | Nutrition | Organisms obtain food/energy |
Plants move too — just much more slowly than animals! A sunflower slowly turns its head to track the Sun across the sky. This response to light is called phototropism.
If something displays all seven of these characteristics, it is considered alive. This is why a fire is not a living thing — it moves, grows, and needs oxygen, but it cannot reproduce or excrete waste in a biological sense.
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