The chemistry of a living body

What are living things?

The coconut tree in the garden, a bird in flight, the mould growing on a stale loaf of bread and bacteria too small to see — all of these are living things. Do you remember how we sorted them into groups in earlier grades?

Have you ever wondered what the bodies of these living things are made of?

If you could magnify a leaf, or one of your own fingernails, far enough, what you would find in the end is chemical compounds. Every one of those compounds is built from a few elements bonded together in different ways. In other words, living things, just like non-living things, are made of elements.

Scientists have so far discovered about 118 elements. Of these, about 92 elements occur naturally in a stable form (that is, they were not made in a laboratory). Only about 25 of them are used to build living bodies. These elements are not gathered in one place in the body. They are spread through different parts such as bone, blood and muscle, as different compounds.