Which concept reflects the biological distinctions between males and females?

The concept that reflects the biological distinctions between males and females is indeed sex. In sociology, "sex" refers specifically to the biological and physiological characteristics that define humans as female or male, such as reproductive organs, chromosomes, and hormonal profiles. This is distinguished from "gender," which pertains to the roles, behaviors, activities, and expectations that societies consider appropriate for men and women.

Understanding this distinction is crucial in sociology, as it allows for an exploration of how social constructs around gender can differ significantly from biological sex. The implications of these concepts extend into various areas, including the study of gender roles, identity, and how society views and treats individuals based on their biological sex.