AP BIOLOGY

Detailed explanation-1: -Denitrification. Denitrification completes the nitrogen cycle by converting nitrate (NO3-) back to gaseous nitrogen (N2). Denitrifying bacteria are the agents of this process. These bacteria use nitrate instead of oxygen when obtaining energy, releasing nitrogen gas to the atmosphere.

Detailed explanation-2: -Nitrification is a two-step process in which NH3/ NH4+ is converted to NO3-. First, the soil bacteria Nitrosomonas and Nitrococcus convert NH3 to NO2-, and then another soil bacterium, Nitrobacter, oxidizes NO2-to NO3-. These bacteria gain energy through these conversions, both of which require oxygen to occur.

Detailed explanation-3: -Stage 5: Denitrification In the fifth stage of the nitrogen cycle, nitrogen returns to the air as nitrates are converted to atmospheric nitrogen (N2) by bacteria through the process we call denitrification.

Detailed explanation-4: -The correct option is D ammonification. When plants and animals die their decomposition leads to to the production of ammonia. There are also some bacteria which convert atmospheric nitrogen into ammonia.

Detailed explanation-5: -Nitrogen is converted from atmospheric nitrogen (N2) into usable forms, such as NO2-, in a process known as fixation. The majority of nitrogen is fixed by bacteria, most of which are symbiotic with plants. Recently fixed ammonia is then converted to biologically useful forms by specialized bacteria.