I don’t normally post in the Traditional Section, but I hope I’m not censured for doing so in response to this question. I have worked in a clinical microbiology laboratory (MT, ASCP) for almost 30 years and consider bacteria and other “little guys” my close buddies.
Yes, there are bacteria that are obligate aerobes, which require oxygen to survive. The best example we see all the time in the lab is Pseudomonas aeruginosa.
There is a huge difference between bacteria and mammals (humans) in the method of reproduction. Bacteria reproduce through binary fission, which means just what the name says–they split and form more of themselves. Mammals reproduce sexually. I don’t need to go into details.
So IMO, an analogy between a living bacteria and a living human being is rather difficult to sustain, as they are from totally different “kingdoms” in the classification systems. Bacteria are part of “Monera” while humans are part of “Animalia,” at least in the old Linnean classification system. I know that there are newer classification systems based on DNA, but in these also, humans and bacteria are far apart. Yes, they have some similiarities their design, but they’re not the same. Therefore IMO, a analogy between Monera and Animalia based on their reproductive methods is an invalid analogy.
I don’t think that any credible scientist will question whether or not a human fetus at any stage of development, including the very youngest zygote, is “living.” Of course it’s living as long as it has not died in utero. It is not viable outside the mother’s womb, just as no mammal is viable outside the mother’s womb. But that does not negate its biology–it is living tissue.
The actual question is, “Is the fetus a human being?” A fetus possesses all the DNA of a human being, so for that reason, many scientists will answer, “Yes, a fetus is a human being based on DNA.”
But many people, including scientists, consider a fetus a “potential human being” because they define “human” as more than just a certain sequence of DNA. This is a dangerous conclusion, IMO. At what point in its development does the fetus become an “actual” human being? Tricky question for the “potential human” crowd to try to answer. Many would say, “When it becomes viable outside the womb.” But this answer is not valid, as many MANY humans are not viable outside of a womb without extraordinary medical intervention. Are these creatures then not actual human beings?
Again, I hope no one objects to my sharing the perspective of a working microbiologist who daily interacts with bacteria.