[Campbell Biology P.631] In the cyanobacterium Anabaena , why do specialized cells called he... | Practice Question
In the cyanobacterium Anabaena , why do specialized cells called heterocysts perform nitrogen fixation instead of photosynthesis, and how do they overcome the challenge of oxygen sensitivity?
A: Heterocysts perform nitrogen fixation because their enzymes are inactivated by oxygen produced during photosynthesis, and their thickened cell walls restrict O2 entry.
B: Heterocysts perform photosynthesis, and other cells perform nitrogen fixation, with O2 freely entering all cells.
C: Heterocysts can perform both photosynthesis and nitrogen fixation simultaneously due to their unique structure.
D: The thickened cell wall of heterocysts allows oxygen to easily enter, facilitating both processes.
Explanation
In Anabaena , photosynthesis produces O2, which inactivates the enzymes involved in nitrogen fixation. Therefore, specialized heterocysts perform nitrogen fixation, and their thickened cell wall restricts O2 entry to protect the nitrogen-fixing enzymes.