What does physiology study?

Physiology is the branch of biology that focuses specifically on the functions and activities of living organisms, including humans. This field of study examines how various systems of the body work together to maintain homeostasis and support life. It encompasses a range of processes such as how organs function, how muscles contract, how blood circulates, and how the body reacts to different stimuli.

The other choices, while related to biological sciences, address different aspects. The study of structures falls under anatomy, which distinguishes itself by focusing on the framework and parts of the body rather than their functions. The study of diseases would typically be associated with pathology, which examines the causes, effects, and progression of illnesses. Lastly, examining the cellular structure of tissues is part of cytology or histology rather than physiology, which takes a broader view by integrating these structures into the context of how they work in the whole organism. Thus, the correct choice clearly reflects the primary focus of physiology on bodily functions and activities.