It doesn't need to be that complicated. If a single cell with chlorophyll can convert light to matter then that is all you need. Cells die, something evolves to use that dead matter to feed on. Voilą you have a food chain.
Admittedly, your method makes much more sense than my hare-brained idea
And there's the added advantage that you don't have to muck about with all that chemistry stuff of actually building the molecules you need to grow out of simpler molecules and elements -they are already there if you ingest something that has done all the hard work for you. Ideally the human body
is the best food for an organism like the human body
-it contains all the vitamins and minerals and whatnot -in the right proportions even