If I was asked to combine the clauses that you mention in your example into a single sentence in order to link the underlying ideas shared by both (rhythm and dancing) I would add a subordinating conjunction such as although and rearrange them as follows:
Although not everyone thinks they have rhythm, dancing can be a fun and active hobby.
The cell theory proposes that all living organisms are made up of cells, who in turn come from other cells, as well as that cells are responsible for the structure and organization of living things.
