What branch of medicine studies the chemical processes within living organisms?

The branch of medicine that focuses on the chemical processes within living organisms is toxicology. Toxicology examines how various substances interact with biological systems, providing insights into the effects of drugs, poisons, and environmental chemicals on health. This includes understanding the metabolism of these substances and how they can cause harm or benefit living organisms.

In contrast, pathology deals with the study of diseases, including their causes and effects on the body, without a primary emphasis on chemical processes. Ophthalmology is concerned specifically with eye diseases and treatment, and radiology focuses on the use of imaging techniques to diagnose and manage medical conditions. Toxicology stands apart by concentrating directly on the biochemical and physiological impacts of chemicals, making it the correct answer in this context.