Explanation about why is it important to have eight hour of sleep every night

Sleeping is one of the most important things you need to do every night.I wonder why you have to sleep just only for eight  hour?what is sleep? sleep is when you close your eyes and your body shuts down and gives you a good nice relaxing time you even begin to start growing.

The reason why it is really important for younger people to have several hour of sleep is because when they go to school they need to pay attention to what the teacher is teaching class which mean you need a good,nice,healthy breakfast and even have a good night rest.