When might a scientist use a model?

For the writer, scientific models are paradigms of set of patterns that is assumed to happen in a particular situation or circumstance which is why it was created and modeled, to explain a certain phenomenon. Take for instance the biogeochemical cycle model –water cycle. The water cycle model involves the different process which was observed happen as the current cycle has been experimented and predicted to happen again with the same process. 

Models can represent things that are too small to see.  Scientists rely on models to represent concepts and processes in physical science because models can represent things that are too small to see. In fact, they are actually used to give a better perspective of what is occurring on these hidden to the naked eye matters –which may include atoms, cells, and entities unseen and latent. It gives scientists the ideas and structure, restructure, integrate and ponder on new hypothesis on these matters.  

What are you trying to ask?