Muscular and skeletal system
The human body
People sometimes call the human body a machine-the most wonderful one ever built. Of course, the human body is not a machine. But it can be compared to one in many ways. Like a machine, the body is made up of many parts. Each part of the body, like each part of a machine, does special jobs. But all the parts work together and so make the body or the machine run smoothly. Also like a machine, the body needs energy to work. In such a machine as a car, the energy comes from petrol. In the body, it comes from food and oxygen. Although the human body can be compared to a machine, it is far more amazing than any machine. It can do things that no machine can do. For example, the body can grow. The body starts out as one cell. In time, this tiny cell develops into a body consisting of trillions of cells.