Digestion is the process of breaking down food into simpler substances. Digestion is of two types: mechanical or physical digestion, and chemical digestion.
Chemical breakdown
It is called digestion.
Catabolism
Digestion
compounds
elements
Substances that cannot be chemically broken down into simpler substances are called elements.
If the above didn't answer your question, a substance that can be broken down into simpler substances is called a compound. Even the simplest compounds can be broken down into individual elements.
That would be an Element.
they are called chemical elements.
Electrolysis is the process by which ionic substances are decomposed (broken down) into simpler substances when an electric current is passed through them.
digestion
This kind of reaction is called "decomposition".
Atom of carbon?
This is called molecule.
A chemical reaction, though often it is not a simpler substance.