Science is the study of anything to do with life or our universe.
Science can study plants and animals because there is physical proof of it and you can literally cut it open and study it.
Science can't study the supernatural or aliens because of the simple fact that there is no proof. You ave to confirm what you see and be able to prove it.
We need things to survive. Such things are water, air, shelter, sunlight, and food.
The ostrich has long legs for running faster. You can get away from predators faster or even catch prey. One behavioral benefit is that they spend winter months in pairs or alone, this is a benefit because it is easier to find a mate that way. Another structural is that they have three stomachs to help grind dirt and rocks. this is a benefit because then they can eat stuff without having to worry about competition over food. They incubate there young for 35-40 days, they do this so they can teach them how to feed.
I think this is a scientific model. We would use a model rather than the real thing to give your perspective on how you look at it. Another reason is so we can recreate that thing without having to take it with us.
A system is a group of things that works together to accomplish something. Systems in our body work together so we can do everyday things such as walk, breathe, and live.
The system in this helps it to move . That is exactly what our body systems do, it helps us accomplish what we are supposed to do.