Which of the following is not true of nitrogen fixation?
(a) it is a process that occurs exclusively in some species of prokaryotes
(b) it sometimes occurs in bacteria that are mutualistic symbionts in plant roots
(c) it is the metabolic process that converts n2 to nh3
(d) it is one of several metabolic processes that make atmospheric nitrogen available for use by other organisms
(e) some species of cyanobacteria have specialized nitrogen-fixing cells

(E) some species of cyanobacteria have specialized nitrogen-fixing cells

Explanation:

The nitrogen is an essential element for life, it's included in the molecule of DNA and RNA. But, most of the nitrogen on the planet is in its inorganic gas form (N₂), which can't be captured for most organisms. But some prokaryotes can metabolic the N₂ to NH₃ in a process called nitrogen fixation. NH₃ can be used by some organisms, and it can be also transformed in nitrate, and then used by the organisms.

Only a few prokaryotes can do this: some bacterias that have a mutualistic symbiont process with plants, and some cyanobacteria of free-life. There is no specialized nitrogen-fixing cell, but there are specialized nitrogen-fixing enzymes.