Question

Which of the following forms of nitrogen cannot be absorbed directly by plants?

• A. NO3-
• B. NO2-
• C. NH3
• D. N2

Answer 1

Answer: (C), (D)

N2

Plants are unable to absorb nitrogen directly from the atmosphere (N2). Rhizobium are nitrogen-fixing bacteria present in roots of leguminous plants which convert atmospheric nitrogen into ammonia (NH3) by the process of nitrogen fixation. The ammonia is converted into absorbable nitrates (NO3-) and nitrites (NO2-) by the process of nitrification. This is done by a bacteria called nitrobacter.