AP BIOLOGY

Detailed explanation-1: -Nitrogen is fixed, or combined, in nature as nitric oxide by lightning and ultraviolet rays, but more significant amounts of nitrogen are fixed as ammonia, nitrites, and nitrates by soil microorganisms. More than 90 percent of all nitrogen fixation is effected by them.

Detailed explanation-2: -The Rhizobium or Bradyrhizobium bacteria colonize the host plant’s root system and cause the roots to form nodules to house the bacteria (Figure 4). The bacteria then begin to fix the nitrogen required by the plant.

Detailed explanation-3: -Symbiotic N-fixing bacteria habituate on the host’s roots, forming nodules, accumulating atmospheric N2 in them, and turning it into ammonia. The host uses it for growth and releases it into the soil from the broken nodules after it dies.

Detailed explanation-4: -There are three processes that can fix nitrogen: atmospheric, Haber Process and biological. Atmospheric fixation occurs when the high temperature of lightning splits the nitrogen gas so it bonds with oxygen and moisture in the air to form nitrates that fall to the earth with rain.