WHEN WE GET DOWN TO THE BITS AND PIECES… WELL… WE’RE ALL MADE OF THE SAME STUFF
Here, we can highlight a hierarchy of how organisms are organized, from the whole organism, to particular tissues (like an organ), to the single cell, to the organelles (like nuclei and mitochondria) within cells, to the molecular structures that form the building blocks of life (like proteins, sugars, fats, DNA), and finally to the individual atoms themselves. Implicit with the view of this organization is the realization that when you get towards the simpler side of the hierarchy, we’re all (and this is the all in terms of everything in the living world) basically made of the same stuff. This means there is remarkable crossover in the scientific knowledge obtained, regardless of the organism you choose to study.
This is huge in terms of how the life sciences work. It means that you can do a lot of work on things that are just easier to work with (say studying a bacteria versus studying a 2nd year university student) and still get a lot of useful information.