Levels of organization: zooming out from an atom

Open Google Maps on your house and keep zooming out: your house, your street, your mohalla, your city, Pakistan, Earth. Same place, but at every zoom level you notice things you couldn't see before — and lose details you could.

Biologists study life the same way. Start with atoms, zoom out to cells, then to a whole organism, and finally to all living things on Earth. Each level has its own features that the level below doesn't have.

Here's a surprise at the very bottom: of the 92 naturally occurring elements, only about 16 are commonly used to build living things. These are called bioelements, and in the human body just six of them — oxygen, carbon, hydrogen, nitrogen, calcium and phosphorus — make up 99% of the mass.