That makes sense Darkblade.
I wonder how effectively plants can utilize citrate in the water column since citric acid is produced from the oxidation of the pyruvate in the mitochondria.
Hard to speculate; you could trace the path of the molecule with radioactive C14, but it is more hassle than it is worth.
One could also speculate that the process is done by bacteria, and that the CO2 generated as a byproduct is absorbed by plants as it diffuses across the cellular membrane.
Basically, glucose crosses the cell membrane. Glycolysis (break the glucose into two pyruvate molecules) occurs in the cytoplasm. Then the pyruvate moves into the mitochondria. We still don't have citric acid. Now we have to oxidize the pyruvates. Finally, after moving into the mitochondria, utilizing multiple enzymes to create the citric acid the kreb cycle can begin. It begins inside the mitochondria not the water column.
To be nitpicky, glucose is transported across the cell membrane, and does not simply cross it.
The process you have described for the metabolism of pyruvate is correct for eukaryotes. The process is similar in prokaryotes, but occurs in the cytoplasm and not in the mitochondria.
I would imagine citric acid would become buffered rather quickly. How much can actually be transported into the mitochondria for the process to start? It doesn't seem a viable way to produce CO2 to me.
It would essentially be buffered immediately upon dissolution in water. I believe there is a plasma membrane citrate transporter that would transport citrate across the cellular membrane, but am unsure as to its actual mechanism of action.
So refreshing to think of cellular biology like this; I have been focusing on a completely different thing for the last 2 years, so it's nice to be able to recall these things