The "Normal" type of Pokemon tends to have a Terran sort of cell structure. In many ways, they behave like normal animals, sometimes being confused for such. However, the "moves" Normal-type Pokemon can use vary greatly from the Earthly norm. With Normal-type powers and abilities, some Pokemon have the capacity to regenerate themselves, move at speeds unknown to other animals, shoot concentrated beams of energy, and even explode.
"Flying" type of Pokemon seem to be some offshoot of the Normal type, and as a rule tend to have wings or some kind of flight apparatus. Like Fighting-type Pokemon, they have hyper-dense muscle, but only in the muscles along and around the wings. This allows Pokemon of the Flying type to generate enormous aerial force, some even able to cut things with their wings or generate G-force winds.
"Bug" types tend to be quite interesting, as they generally share a symbiotic relationship with a sort of non-Pokemon creature, the Blood Mite (Sanguiparvulus utiliparasitus), living in its blood stream. Such Pokemon of the Bug type end up resembling Earth arthropods themselves, as well as acquiring some abilities shared with arthropods here on Earth (sapping bodily fluids, generation of silk, etc.). Most of the Bug types have exoskeletal armor along with their internal skeletons, which tend to be weaker as a result.