Question

why does nitrogen have to be \fixed\? what organisms are responsible for nitrogen fixation? (site 2)

Explanation:

Nitrogen gas in the atmosphere is inert. It needs to be fixed to be converted into a usable form like ammonia or nitrate for plants and other organisms. Certain bacteria, such as Rhizobium (in symbiotic relationship with legumes) and free - living bacteria like Azotobacter, are responsible for nitrogen fixation.

Answer:

Nitrogen has to be "fixed" because atmospheric nitrogen is inert and cannot be directly used by most organisms. It needs to be converted into a more reactive form like ammonia or nitrate for uptake by plants and incorporation into biological molecules. Organisms responsible for nitrogen fixation include certain bacteria such as Rhizobium (which forms a symbiotic relationship with legumes) and free - living bacteria like Azotobacter.