Calculate the amount of ATP required by nitrogen fixer for the formation of 1000 molecules of ammonia. Name the specialised cell of cyanobacteria where nitrogen is fixed.

Q.14 Calculate the amount of ATP required by nitrogen fixer for the formation of 1000 molecules of ammonia. Name the specialised cell of cyanobacteria where nitrogen is fixed.

Doubtly Asked 28 Oct 2026 Board exam · March 2026 hsc 12th Save WhatsApp Report

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Answer: 8000 ATP; heterocyst.

Biological nitrogen fixation (by nitrogenase): N₂ + 8e⁻ + 8H⁺ + 16 ATP → 2NH₃ + H₂ + 16 ADP + 16 Pi

So 2 molecules of NH₃ need 16 ATP, i.e. 8 ATP per molecule of ammonia.

For 1000 molecules of NH₃: 1000 × 8 = 8000 ATP.

In cyanobacteria (e.g. Nostoc, Anabaena), nitrogen is fixed in thick-walled specialised cells called heterocysts.

Doubtly AI · 28 Oct 2026 AI-verified · Oct 2026 Report

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Calculate the amount of ATP required by nitrogen fixer for the formation of 1000 molecules of ammonia. Name the specialised cell of cyanobacteria where nitrogen is fixed.

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