Histology primarily focuses on the study of what?

Histology is the branch of biology that examines the microscopic structure of tissues. It delves into how tissues are organized and how their composition contributes to their functions within the body. Understanding histology is crucial for various fields, especially in health and medicine, because it provides insights into how tissues respond to stress, injury, and disease.

While studying the structures of the human body (the first option) plays a role in histology, it is more comprehensive in its focus on the intricate details of tissue types, which include connective, epithelial, muscle, and nervous tissues. The functions of organs (the second option) involve understanding how those organs operate, but histology emphasizes the tissue composition that forms the organs, serving as a foundational aspect for their function. Physical activity in the body (the fourth option) relates to biomechanics and physiology rather than the cellular and tissue structures that histology investigates. Therefore, the core focus and essence of histology lie in the structure and composition of tissue, making that the correct answer.