Why is a living thing a system?

Any living thing has multiple things going on in it's body at one time and all are working on separate or similar tasks in the organism, therefore they work as a system.

Living things is related to one another. I think thats why they are called as a system.

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Aform of energy that is reflected or emitted from objects in the form of electrical and magnetic waves that can travel through space. there are many forms of  electromagnetic  energy including gamma rays, x rays, ultraviolet radiation, visible light, infrared radiation, microwaves and radio waves.