Here's why:

* Atoms are the smallest unit of an element that retains the chemical properties of that element. They are the building blocks of all matter, including you, the air you breathe, and the chair you're sitting on.

* Molecules are formed when two or more atoms bond together.

* Cells are the basic unit of life, and they are made up of many different types of molecules.

So, while molecules and cells are important levels of organization, they are built upon the foundation of atoms.