Biochemistry is the science that looks at living things through chemistry. It asks what molecules are doing in a cell: how food becomes energy, how DNA is copied, how a vitamin helps a reaction, why a poison stops one. In school it sits between biology and chemistry, and you need a little of both. Doctors use it every day without always saying the long word — a hospital “biochem” blood panel is biochemistry at work. Though actually, the tidy dictionary makes it sound like one neat box. In real labs the edges blur into molecular biology, physiology, and nutrition. People still say biochemistry when they mean “the chemistry of the body or of cells”. It is a formal school-and-lab word; in casual talk someone might just say “body chemistry” and be understood, if not precise.