Biology is an extremely broad subject because it is defined as the study of all living organisms. The branches of biology typically focus on a single topic or problem that can usefully be grouped together, such as the study of fish or the development of embryos. It is possible to study the same topic within different areas of biology, albeit from different perspectives. Some commonly known types biology include ecology, genetics, and biochemistry. There are many minor branches of biology, and people proposing that certain topics be included as branches must consider whether this isolation is useful from a practical standpoint.
Some of the most common branches of biology deal with one type of living organism and tend to look at all aspects of that organism, including cellular, physical, and evolutionary development. Mycology, for example, is the biological study of fungi, and ichthyology is the study of fish. Broader branches of biology include zoology, the study of animals, and botany, the study of plants.
It is also possible to look at biology in terms of what level of the organism is being studied. Anatomy, for example, is the study of broad physical form, cell biology is the study of cells, and molecular biology is the study of biology on the level of molecules. Within organisms, it is possible to look at specific biological systems, as is the case in neurobiology.
Often, biology looks at processes rather than states, as is the case with evolutionary biology. Sometimes, biological studies are primarily theoretical, which is true of astrobiology, the study of life on other planets and throughout the universe. Biology can also be used to study organisms that no longer exist using physical remains. Ethology, the study of animal behavior, looks not at the physical form of an organism but at its instincts and activities. Sociobiology similarly studies sociological behaviors from a biological stance.
In some cases, branches of biology work on solving existing problems rather than describing how the world works. This is certainly the case with biomechanics, which has as its primary focus the integration of humans with prosthetic devices, and agriculture, which studies the ways in which humans can cultivate plants. Conservation biology is unique because it attempts to conquer the question of how to preserve the current state of the earth for as long as possible, which is a uniquely human concern. From these examples it is clear that humans often use branches of biology not only to talk about the world but also to attempt to fix problems like serious diseases, the extinction of various species, and even moral concerns about living organisms.