The reason we teach biology as a purely descriptive course is that it's really so complex that few teachers can handle its full details. So these courses get taught independently of each other. Chemistry in turn is laced with concepts from the physics course that students haven't yet taken. So science begins to look like no more than a recitation of words. Students have little basis for appreciating the structural way the concepts bind one another together.
Science is quite different from, say, history.
Humanities students develop maturity in a mosaic fashion. Learn about Byzantium one semester and English kings the next. The order isn't important, because the big picture emerges from many tiles. Far more than biology, history is too complex to be based on simple sequences. To teach science, we have to reveal a mathematical and logical structure that comes to rest on concepts and equations.