Which of the following best defines physiology?

Physiology is best defined as the study of the functions and processes of living organisms. This encompasses how various systems within an organism, including cells, tissues, organs, and systems, work together to support life. It investigates processes like metabolism, respiration, reproduction, and homeostasis, providing insight into how organisms respond to their environment and maintain internal stability.

The other options, while related to biological science, do not capture the broad and dynamic essence of physiology. For example, the study of disease processes focuses specifically on pathological changes, which is a narrower field within medicine and biology. The study of cell structures pertains more to cytology and anatomy rather than physiology. Lastly, focusing solely on body organs limits the scope of physiology, as it encompasses not just individual organs but also their functional interrelationships and systems within living organisms. Thus, the accurate and holistic definition of physiology aligns with the study of how living organisms function as a whole.