What is chemsity and what does it have to do with science

Chemistry is the study of the composition of matter and the ways in which matter interacts, combines, and changes under certain conditions.  Although not as fundamental as physics, chemistry is a very basic and broad science.  It helps us explain bodily interactions and natural process (biochemistry), it helps us to manufacture new medications, and true chemistry research will always follow the scientific method.

Because a model would make the investigation easier to understand