So in this sense then, human beings themselves are obligate metabolic parasites on the planetary ecosystem, particularly on other life forms (plants, animals, microbes). The term "parasite" here is used in the metabolic sense of relying on another organism to produce essential compounds one cannot produce oneself. The molecules we must obtain fully synthesized from our diet are called essential nutrients. And for a Sukunaarchaeum, everything is an essential nutrient.

Agent Smith said a virus: https://www.youtube.com/watch?v=L5foZIKuEWQ

yeah, but he was biased against humans because of their smell. Though a virus might not be accurate.

Are there any animals which don’t need components from another organism? Isn’t heterotrophy one of the notable attributes of Animalia? There are the infamous sea slugs which eat algae then use the algae’s photosynthetic chloroplasts to photosynthesize the chemical energy they need, but they still need the algae to make those chloroplasts.

Interesting to realize that all animals are parasites (or perhaps symbiotes in some rare cases?) when you zoom out and look at the big picture. Almost makes me feel a bit guilty for not being a self-sustaining plant.

As I understand it, it's not so much that they got "hung up" on some specific capabilities for theoretical reasons, but that it's rare to find cells without these capabilities. In other words, it's nature that seemed so "hung up" on these things.

well people want simple models and explanations -- just like physicists want to model cows as "spherical boing boing cows"

We can survive without a constant stream of incoming raw materials. I wouldn’t think that makes us any less alive. Nor are we a parasite on the food.

You could make a distinction here in that we only need raw materials, we don't need another organism to reproduce. Mosquitos can also easily consume raw materials in the form of nectar to survive, but they need to take blood from other animals if they want to reproduce. If you go along this chain of thought, you can come up with arbitrary definitions.

We need mitochondria.

They are technically no longer individual life forms. They sure used to be, but we merged quite some time ago. Of course that opens a whole other can of worms with respect to who you really are. You're trillions of microorganisms living together and quite a few of them don't even share your DNA.

We need 20 different amino acids to build all our proteins. We can synthesize 11 of them (non-essential amino acids), but we must obtain the other 9 Essential Amino Acids fully formed from the food we eat.