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Difficulty: HardKingdom Monera: Bacteria and Cyanobacteria

In nitrogen-fixing filamentous cyanobacteria, specialized cells called heterocysts lack Photosystem II activity, thereby preventing oxygen production that would otherwise inhibit the enzyme nitrogenase.

Answer: Answer

Answer

The statement is TRUE.
Heterocysts are specialized cells in certain cyanobacteria (such as Anabaena) adapted for nitrogen fixation. Because nitrogenase is oxygen-sensitive, heterocysts modify their photosynthetic apparatus to eliminate Photosystem II, preventing internal oxygen generation while retaining Photosystem I for ATP production.

Step-by-Step Solution

1
Analyze the oxygen sensitivity of nitrogenase during prokaryotic nitrogen fixation.
The nitrogenase enzyme complex reduces atmospheric nitrogen (N2N_2) to ammonia (NH3NH_3), but it is highly sensitive to molecular oxygen (O2O_2) and rapidly denatured by it.
Understanding enzyme inhibition by oxygen is required to analyze prokaryotic adaptation strategies.
2
Examine structural and photosynthetic modifications in cyanobacterial heterocysts.
Heterocysts undergo specialized cellular differentiation wherein Photosystem II is inactivated (stopping O2O_2 generation), while Photosystem I remains active to supply ATP via cyclic photophosphorylation.
This spatial separation isolates oxygen-producing photosynthesis in vegetative cells from nitrogen fixation in heterocysts.
3
Determine the truth value of the given statement.
Because heterocysts specifically lack Photosystem II to protect nitrogenase from oxygen inhibition, the statement is accurate.
The physiological mechanism stated aligns directly with cyanobacterial biochemistry.

Key Concept

Cellular specialization for nitrogen fixation in Cyanobacteria (Heterocysts)
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Topics

Kingdom Monera: Bacteria and Cyanobacteria

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