Studying biology is like learning a new language. There are lots of new words. There are lots of new concepts. You even have to express yourself in a different way.
There is a section containing the core vocabulary – everything from abiotic to zoologist. The next section outlines the work of the scientists studied in the Biology course. The next two sections are the Option sections – Communication and Genetics. It was better to keep them separate so as to keep the course content clear. People studying genetics do not need to know about the ciliary organ, for example. Neither do the students of communication need to know all about transposable elements.