PLZ HELP! Nitrogenase, the enzyme that catalyzes nitrogen fixation, is inhibited whenever free O2 reaches a critical concentration. Consequently, nitrogen fixation cannot occur in cells wherein photosynthesis produces free O2. Consider the colonial aquatic cyanobacterium Anabaena, whose heterocytes are described as having "a thickened cell wall that restricts entry of O2 produced by neighboring cells. Intracellular connections allow heterocysts to transport fixed nitrogen to neighboring cells in exchange for carbohydrates." Given that the enzymes that catalyze nitrogen fixation are inhibited by oxygen, what are two "strategies" that nitrogen-fixing prokaryotes might use to protect these enzymes from oxygen? A) Package them in membranes that are impermeable to all gases, and package these enzymes in specialized cells or compartments that inhibit oxygen entry
B) Be obligate anaerobes, and package these enzymes in specialized cells or compartments that inhibit oxygen entry
C) Be obligate anaerobes, and be facultative aerobes
D) Be facultative aerobes, and package these enzymes in specialized cells or compartments that inhibit oxygen entr