The orgin of eukaryotes was a precondition of multi-cellularity and increased complexity of organisms. Again, the first eukaryotes had a more flexible morphology than prokaryotes. This led to the evolution of organelles and the separation of cellular function. Eventually, colonies of these eukaryotic cells emerged such that a division of labor occured where certain groups of cells reproduced, others fed, and so forth. In our labs on soil biodiversity, we provided you with several different types of media for growing soil microorganisms.
Different organisms have different growth requirements and growth rates.
By using several different media we provided a greater number of different growing environnments in which to potentially capture a greater number of different species living in the samples than had we only used one media. In order to capture the thousands of microrganisms living in a pinch of soil, we would need to provide for the necessary growth conditions of each species - temperature, acidity, air pressure, appropriate nutrients, etc. Of the organisms that we know exist, we cannot account for all of the conditions required to grow them. In addition, there are many more organisms, whose existence is yet undiscovered, and for which we would most certainly miss using the techniques we used. A large mountain lake is separated into two lakes by a volcanic eruption, leading to a barrier between populations of an aquatic beetle.