To fix the semantics of different kinds of parthood relations we require axioms which go beyond those characterizing partial orderings. I formulate such axioms and show their implications for bio-ontologies. Specifically, I discuss parthood relations among masses, for example among body substances such as blood and portions thereof, and among components of complexes, for example between your stomach and your gastro-intestinal system. I contrast these with the relation of being contained in (as your lungs are contained in your thorax). The axioms considered are rooted in mereology, the formal theory of parts and wholes. By making explicit the differences between the different kinds of relations they support different kinds of data integration in bioinformatics.