Biology is a natural science discipline that studies living things. It is a very large and broad field due to the wide variety of life found on Earth, so individual biologists normally focus on specific fields. These fields are either categorized by the scale of life or by the types of organisms studied. Scale of Life For example, the scale of biology can cover everything from genetics, biochemistry and molecular biology – studying the molecules of life inside our cells and how they help us function – to cell biology which focuses on the basic unit of life. There is also anatomy, physiology and other fields that focus on whole organisms, and to even larger scales such as animal behavior, population biology, and ecology and systematics that study groups and entire communities of organisms.