Living things, including all organisms on Earth, are composed of both atoms and molecules. Atoms are the basic building blocks of matter, and they combine to form molecules. Molecules are groups of two or more atoms held together by chemical bonds.
In living organisms, atoms of various elements such as carbon, hydrogen, oxygen, nitrogen, and many others come together to form different types of molecules. For instance, carbohydrates are composed of carbon, hydrogen, and oxygen atoms arranged in specific structures. Proteins are made up of chains of amino acids, which consist of carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur. Nucleic acids, such as DNA and RNA, are composed of nucleotides containing atoms of carbon, hydrogen, oxygen, nitrogen, and phosphorus.
These molecules, in turn, interact with each other and with other cellular components to form the complex structures and systems found in living organisms. So, while living things are ultimately composed of atoms, it is the arrangement and interaction of molecules that give rise to the diversity and complexity of life.