Differentiated tissues take more time to develop than do undifferentiated tissues. bacteria, for example, reproduce a new generation every 20 minutes, but humans take about 20 years. bacteria occupy more ecological niches than humans occupy and have much more total biomass. what, if any, is the advantage of differentiation?

One of advantage of differentiation is that organisms with differentiation are larger. Larger organism live longer and have bigger possibility to fight against predators and find food. Second, organisms can built of multiple component parts that have different functions. Third, that organisms can better protecting genes from the damage of mutagens.

Yes it would be a physical change.