"the question of where an organism begins and ends"
Ludwig [or Ludwik] Fleck ([1935] 1980), observed that the bacteria in human intestines meet the requirement of an organism as a "viable whole," though also notes that they are considered to be treated as part of the larger system of a human
However, following this logic to its extension: "the entire ecosystem of which humans play a part may well be designated as a viable whole--an organism--in its turn. Opening up the boundaries around what seemed a self-evident whole, the organism, goes together in Fleck's text with opening up the boundaries of science. That, too, he shows, is not an impermeably closed off self. Its boundaries leak."
see his Genesis and Development of a Scientific Fact