The living beings which inhabit the earth are all very different both in size and in form. However, they all have something in common and that is their chemical composition.

If we analyse living matter, in other words the thing which makes up living beings, we find some elements in large quantities:carbon, oxygen, hydrogen and nitrogen.Of all these elements carbon is the one that really characterises living matter.

Atoms of carbon can be combined with many other atoms to form a wide variety of molecules. Some of these molecules are very big (like proteins). It is these molecules that form living matter.--81.184.59.173 12:49, 5 November 2005 (UTC)Cristina