Biology (also referred to as the biological sciences) is the science of life. It is the scientific study of the structure, function, growth, origin, evolution, and distribution of organisms. From a ToK perspective, organisms are objects behaving at the second dimension of complexity.

Four unifying principles form the foundation of modern biology:

There are a large number of biological science disciplines. A few of the more prominent include botany (the study of plants); zoology (study of animals); microbiology (microorganisms); cytology (study of cellular function); evolutionary biology (mechanisms and processes of evolution); physiology (the physical and chemical functions of the tissues and organ systems); and ecology (how organisms and their environment interrelate).