What is a molecule? what are some molecules found in the human body?

in a simple way .

a molecule is made up of atoms or ions

some molecules found in the human body are H20 or CO2 or O2

affects the water bodies: excessive use of fertilizers causes eutrophication. the fertilizers which are used on plants affect the quality of land on which it is used, further causing erosion of soil. the fertilizers used on plants contain harmful chemical fumes which affect the environment.