Why do I sleep?

What happens if you don't sleep well? Which parts of your body never sleep? How many hours of sleep does your body need? Find the answers to these questions and much, much more in this picture-packed introduction to the human body. An ideal first introduction to biology and health, Science in Action explores the human body with fun experiments and activities. What happens if you don't sleep well? Which parts of your body never sleep? How many hours of sleep does your body need? Find the answers to these questions and much, much more in this picture-packed introduction to the human body. An ideal first introduction to biology and health, Science in Action explores the human body with fun experiments and activities.