Question

Why is nitrogen fixation so energetically costly?

Short answer

Biological nitrogen fixation is an energy-costly process because 16 ATP molecules are required to break down a single${\mathrm{N}}_2$ molecule. The${\mathrm{N}}_2$ molecule is nitrogen that isn't "fixed." an extremely powerful triple connection exists between the two nitrogen atoms.

Step-by-step solution

Nitrogen fixation.  

Comparing biological nitrogen fixation to the Haber-Bosch process for the commercial manufacture of ammonia ${\mathrm{N}}_2$and ${\mathrm{H}}_2$ demonstrates the amazing nature of this process, which takes place at ambient temperatures and pressures. When${\mathrm{N}}_2$ is fixed, the nitrogen is taken up by biological molecules in the form of amino groups, which can then be transferred to other molecules.

To break the N2 bond, need energy.  

The ${\mathrm{N}}_2$ molecule is a kind of unfixed nitrogen. A powerful triple bond holds the two nitrogen atoms together. Breaking this relationship requires a lot of energy. Natural gas is the source of hydrogen, which is required to generate ammonia. The permanent form of nitrogen is ammonia. Nitrates are the alternative form of fixed nitrogen. It takes producing ammonia, followed by oxidizing it, to produce nitrates.

16 ATP hydrolyzed for N2 reduction.

On the MoFe-protein${\mathrm{N}}_2$ is reduced in three separate stages that each requires an electron pair. Therefore, 8 electrons were transported, and 16 ATP were hydrolyzed as the overall cost of$N_2$ reduction. Under cellular circumstances, the cost is more in the 20–30 ATP range. Therefore, nitrogen-fixing is a costly process in terms of energy.