What would any living organism do without oxygen?

For hundreds of millions of years Oxygen has been poisonous to life on earth. Life on earth (written large) evolved over time to be able to cope with, and eventually rely on, oxygen. On Earth, though, there are also many species that can survive for unlimited periods without oxygen, and others (called obligatory anaerobes) for which oxygen is poisonous, and can only exist in oxygen-free conditions.

~MistyMia~

I hope this helps and was what you were looking for.

the cell cycle is the final answer! : )

hydrogen is a compound or a single element and a element is a pure substence that cannot be separated into simpler subtances

clorine is a compound its a chemical substance that forms when two or more different elements combine

so both hydrogen and clorine are compounds