Match each soil microorganism involved in the nitrogen cycle with its specific biochemical… — JAMB UTME

Match each soil microorganism involved in the nitrogen cycle with its specific biochemical transformation role.

NitrosomonasConverts ammonium ions ( $NH_4^+$ ) into nitrites ( $NO_2^-$ )
NitrobacterConverts nitrites ( $NO_2^-$ ) into nitrates ( $NO_3^-$ )
PseudomonasConverts nitrates ( $NO_3^-$ ) into gaseous nitrogen ( $N_2$ )
AzotobacterFixes atmospheric nitrogen gas ( $N_2$ ) directly into ammonia/organic nitrogen independently in the soil

Answer

Nitrosomonas matches conversion of ammonium ions to nitrites; Nitrobacter matches conversion of nitrites to nitrates; Pseudomonas matches conversion of nitrates to gaseous nitrogen gas; Azotobacter matches free-living nitrogen fixation.

Each microorganism carries out a specific metabolic step in the nitrogen cycle: Nitrosomonas converts ammonium to nitrites, Nitrobacter converts nitrites to nitrates, Pseudomonas performs denitrification returning nitrogen gas to the atmosphere, and Azotobacter carries out free-living nitrogen fixation.

Step-by-Step Solution

Identify nitrifying bacteria

Nitrosomonas oxidizes ammonium to nitrite, while Nitrobacter oxidizes nitrite to nitrate.

Nitrification occurs in two distinct aerobic enzymatic stages.

Identify denitrifying bacteria

Pseudomonas reduces soil nitrates to nitrogen gas (

N_2

Denitrification reduces available soil nitrogen under oxygen-depleted soil conditions.

Identify free-living nitrogen-fixing bacteria

Azotobacter fixes atmospheric

N_2

independently without forming root nodules.

Distinguishes nonsymbiotic nitrogen fixers from symbiotic species such as Rhizobium.

Key Concept

Bacterial Roles in the Nitrogen Cycle

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