A system is an assemblage of parts, working together, forming a functioning whole.

A general term to mean either a transfer or transformation of energy or matter

Both matter and energy are exchanged across the boundaries of the system (Organic)/e.g: Human

Energy but not matter is exchanged across the boundaries of the system (e.g atoms, Earth)

A model is a simplified description designed to show the structure or workings of an object, system or concept