Q2 / 200 · MHT CET - Medical 2026 (26 April Shift 1) · Biology

Given below are two statements regarding nitrogen fixation in plants.
Statement I - Nitrogen fixing bacteria use high energy to fix each molecule of nitrogen to form ammonia, which is an exothermic reaction.
Statement II - Chemoautotrophic bacteria obtain energy during nitrification of ammonia into nitrate, which is an endothermic reaction.
In the light of the above statements, select the correct option given below:

  • A
    Both statement I and statement II are correct.
  • Correct answer
    B
    Both statement I and statement II are incorrect.
  • C
    Statement I is correct but statement II is incorrect.
  • D
    Statement I is incorrect but statement II is correct.

Solution

Statement I is incorrect because biological nitrogen fixation requires a very high input of energy ($8$ ATP for each $\text{NH}_3$ produced). Since it requires energy, it is an endothermic process, not an exothermic one.

Statement II is incorrect because nitrification involves the oxidation of ammonia into nitrite and then into nitrate. Oxidation reactions release energy, making nitrification an exothermic process, not an endothermic one. Chemoautotrophic bacteria utilize this released energy to synthesize their food.

Therefore, both Statement I and Statement II are incorrect.

Answer: Both statement I and statement II are incorrect.

Hence, the correct answer is option: 'B'.

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