Discussion
Transformation of normal cyanobacterial cells into heterocysts involves
Answer: A
Heterocyst formation involves synthesis of nitrogenase and retention of photosystem I.
Nitrogenase is destroyed by oxygen, so filamentous cyanobacteria such as Anabaena fix nitrogen in specialised heterocysts. During differentiation the cell builds a thick glycolipid and polysaccharide envelope that limits oxygen entry, switches on the nif genes to make nitrogenase, and dismantles photosystem II, the oxygen-evolving photosystem. Photosystem I is kept, because cyclic electron flow around it supplies the large amount of ATP that nitrogen fixation needs.
Losing photosystem I would leave the heterocyst short of ATP, so the options with loss of photosystem I are wrong, and the options with loss of nitrogenase contradict the whole purpose of the heterocyst, which is nitrogen fixation.
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