For example, the human organ interactions are studied as part of the body system, even though the body cannot exist without food, air, water, et cetera. Heat and light from the sun, minerals from the earth, and water build life. The water cycle, combined with the ocean currents, move nutrients and moisture necessary for life. This subsystem greatly impacts weather patterns and life. Whale adaptations studied.
Limbs work as levers.
The systems are bound together in a unit. Scale denotes magnitude. Blowing wind varies from a baby's breath to a hurricane. Size is relative to the viewer and distance. Structure describes the form of an object.