Children are often told that the small unit of life is the cell when we are studying plants, animals, and people (life science).
But, in physical science, we are told that the smallest unit of matter is the atom.
They are both true.
Living Things are made up of matter that is made up of atoms and molecules, too.
You see a cell has many components like ribosomes, mitochondria, and lysosomes. These components are made up of large molecules and the molecules are made up of atoms.
Proteins, sugars, and fats are all molecules. The oxygen that your cells so desperately need is a molecule.
Inside the cell, chemical reactions are happening all the time! Inside the cell, you will find atoms as part of molecules. Their electrons in an atom are busy beavers participating in all kinds of movement during the chemical reactions that keep a person alive. In the cellular level, the processes that provide oxygen (respiration), energy (glucose), and building things like antibodies are pure chemistry!