What living things need — Biology, 7–10 years
Living things are active: they need materials and energy to grow, repair themselves and stay alive.
The basic needs of life
A living thing must get what helps it stay alive. Animals need water, air, food and a suitable place; plants need water, air, light and space. They also grow and make more of their own kind, although not always in the same way.
Why look for signs of life?
People often find things that move, grow or change, but movement alone does not prove that something is alive: a toy car moves too. Scientists needed a fair way to compare a seed, a cat and a stone. Looking for several signs together makes the judgement more reliable.
Example: a seed on a windowsill
Put a bean seed on damp cotton and check it each day. After two days, a root appears; after five days, a shoot rises and its leaves open. It has taken in water, used stored food for energy and grown. A dry pebble may get warm, but it does none of these things.
The moving-object mistake
It is easy to call a fire, a cloud or a robot alive because each one moves or changes. That is a reasonable first guess: living things do move and change. The stronger test asks whether the thing takes in materials, uses energy, grows or repairs itself, and produces new living things.
Choosing care for a living thing
Knowing what life needs helps you care for a plant or pet. A basil plant on a dark shelf may need light and water, while a rabbit needs food, clean water, air, space and safe shelter. The right care depends on the kind of living thing, not on one rule for everything.
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