Zoology Q59 – AP-EAMCET 2025

Home Zoology Microbes in Human WelfareQuestion #30

This bacterium convert nitrites into nitrates.

Clue 1 of 3: The Nitrogen Cycle

The nitrogen cycle is a biogeochemical cycle by which nitrogen is converted into multiple chemical forms as it circulates among atmospheric, terrestrial, and marine ecosystems.

🧠 Full Solution Path

Step 1: Understand the Nitrogen Cycle and Nitrification✦ Active

The nitrogen cycle is a crucial biogeochemical process that transforms nitrogen into various chemical forms. Nitrification is a key part of this cycle, involving the oxidation of ammonia to nitrite and then nitrite to nitrate. This process is carried out by specific groups of bacteria.

💡 Teacher's Secret Hint

Remember that nitrogen fixation, ammonification, nitrification, and denitrification are the main stages of the nitrogen cycle, each involving different microorganisms.

Step 2: Identify the First Stage of Nitrification○ Expand

The first stage of nitrification is the oxidation of ammonia ( $N H_{3}$ ) to nitrite ( $N O_{2}^{-}$ ). This step is primarily performed by bacteria such as *Nitrosomonas* and *Nitrosococcus*.

2 N H_{3} + 3 O_{2} \to 2 N O_{2}^{-} + 2 H^{+} + 2 H_{2} O

💡 Teacher's Secret Hint

This step is called nitrosofication.

Step 3: Identify the Second Stage of Nitrification○ Expand

The second stage of nitrification involves the oxidation of nitrite ( $N O_{2}^{-}$ ) to nitrate ( $N O_{3}^{-}$ ). This specific conversion is carried out by bacteria belonging to the genus *Nitrobacter*.

2 N O_{2}^{-} + O_{2} \to 2 N O_{3}^{-}

💡 Teacher's Secret Hint

This step is called nitratification.

Step 4: Match the Bacterium to the Given Conversion○ Expand

The question asks for the bacterium that converts nitrites into nitrates. Based on Step 3, *Nitrobacter* is responsible for this conversion.

💡 Teacher's Secret Hint

Pseudomonas is involved in denitrification, and Thiobacillus is a sulfur-oxidizing bacterium, not directly involved in the nitrification steps described. Nitrosococcus is involved in the first step of nitrification (ammonia to nitrite).

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Zoology Question 59 – AP-EAMCET 2025

Clue 1 of 3: The Nitrogen Cycle

🧠 Full Solution Path