1. how is modeling useful to scientists?

A model can help scientist to study the things that are difficult to understand that can not be observed directly. It allows scientists to examine and visualize that might not be accessible physically. All the natural science is based on the models, these are suggested and tested by observations.

A model is useful to scientists because it helps show what they have experimented and evidence that it works.

It's either -limiting factors or -scarce resources but i'd go with my first answer since the food and water are abundant they really aren't scarce