If an organism can grow on both nutrient agar and hektoen enteric agar, which would be better & why?

Answer 1

It depends on your purpose. Hektoen enteric agar is a selectic medium for enteric bacteria. It is good for isolation of enteric bacteria and for diagnosis purpose. For axenic culture (pure culture), a general medium such as nutrient agar should be better.

Answer 2

yes. as you noted viruses do not but I really question the definition of life. I think that it is actually very difficult to define life per say because self replicating proteins were the first things to happen. So when did life begin? Cell walls? You can see where this goes.