Ramblings

Of all the elements in the periodic table, six are the most abundant in living organisms: carbon, hydrogen, nitrogen, oxygen, sulfur, and phosphorus. The goal of life is to obtain these elements in a form that they can be used in directly, or to synthesize them into a useable form. Also, once obtained, these elements are required for different things. Sometimes an organism needs oxygen because it is an element that is part of a structural molecule the organism is synthesizing (think - a starchy cell wall). But sometimes oxygen is necessary because an animal needs it to get energy out of it (for example, to power the building of that starchy cell wall).

The question is - what are the useable forms of those elements, and how are those useable forms created. For example, we don't make the vitamin B12 but we do require it to live. Is there an abundance of vitamin b12 on the earth already, or does it have to be made? If we don't make it, what does? How does it make it?

These are fundamental questions in biology, and an emerging theme is that eukaryotes (roughly, organisms with a nucleus, many of which are multicellular) aren't great at making their own nutrients. Single celled prokaryotes, different from eukaryotes n several ways includng being anucleate and unicellular, are great at synthesizing these molecules from materials that are not useful to humans. For example, Escherichia coli cells in the human astrointestinal tract synthesize vitamin B12 that we subsequently take up and use. The emerging model is that eukaryotes use prokaryotes n symbiotic associations to live in places they otherwise couldn't live because the prokaryotes provide nutrition to the eukaryote, just as in the example above.

More on this later - i was trying to build up to another cool association, but took too long getting there.