Based solely on logic (i.e. don't believe anything until others with experience chim in):
1) I'd guess so. I haven't seen much for white photosynthetic organisms in our tanks
2) based on #1, I don't have a clue
3) again, logic says flow comes from A. If flow came from B, I find it hard to believe that the gorg would grow into the direction of more resistance.
I could be completely wrong, but I wanted to take a stab at it.