When we look at the world, we can usually tell the difference between a living creature—like a playful puppy—and a non-living thing, like a rock. But what exactly makes that puppy alive while the rock isn’t? And why does it matter? Let’s dig in! 

A not very long list needs to be considered to define a living being. Let's call it checklist for life.

• Grow and develop – from a seed to a tree, or a tadpole to a frog.

• Reproduce – creating new life, either on its own (like bacteria) or with a partner (like us humans).

• Respond to its environment – have you ever seen a flower lean toward the sun? That’s life in action!

• Use energy – plants use sunlight, animals eat, and even tiny cells break down nutrients to fuel their activities.

• Maintain homeostasis or “keeping balance,” like our bodies staying warm even on a cold day.

These five traits are part of what scientists call the “characteristics of life.” If something meets these conditions, it’s considered alive.

Some things, like viruses, challenge this distinction, as they only show some life traits when they’re in a living host. This makes them a bit like "halfway" creatures in the world of science.