Physiology is best defined as?

Physiology is best defined as the study of the functions of living organisms. This field focuses on how various systems within an organism work, interact, and contribute to the overall functioning of life. It encompasses understanding processes such as respiration, circulation, digestion, and homeostasis, among others. By exploring the mechanisms behind these processes, physiology provides insight into how living beings maintain life, adapt to their environments, and respond to challenges.

The other options do not encompass the core focus of physiology. For instance, the study of body structure pertains more to anatomy, while the study of the environment could relate to various fields, including ecology or environmental science, rather than physiology specifically. The study of nature is too broad and does not directly relate to the mechanisms of life functions, which is the essence of what physiology seeks to explain.