Final answer:
Everything in the universe is made of elements, which are the simplest building blocks of matter. These elements are composed of atoms, which can combine to form molecules, and are fundamental to all matter, including the human body.
Step-by-step explanation:
Almost every situation that you can imagine involves chemistry, because everything in the universe is made of elements. To study the chemical level of organization, scientists consider the simplest building blocks of matter: subatomic particles, atoms, and molecules. All matter in the universe is composed of one or more unique pure substances called elements, familiar examples of which are hydrogen, oxygen, carbon, nitrogen, calcium, and iron.
The smallest unit of any of these pure substances (elements) is an atom. Atoms are made up of subatomic particles such as the proton, electron, and neutron. Two or more atoms combine to form a molecule, such as the water molecules, proteins, and sugars found in living things. Molecules are the chemical building blocks of all body structures.
These elements must have been made (fused) somewhere in the universe, and the only place hot enough to make them is inside stars. This is one of the fundamental discoveries of twentieth-century astronomy. Moreover, there are 118 elements, but only 92 occur naturally. The remaining elements are synthesized in laboratories and are unstable. Each element is designated by its chemical symbol, such as C for carbon and Ca for calcium.