Question

Choose the correct sequence of events occuring in the nitrogen cycle.

i. The nitrogen compounds from dead plants re-enter the soil after decomposition by bacteria and fungi.
ii. Once nitrogenous compound is formed, plants utilise it to form proteins.
iii. Certain bacteria in the soil convert the atmospheric nitrogen into compounds of nitrogen.
iv. Certain bacteria convert the compounds of nitrogen back to gaseous nitrogen.

• A. i - ii - iii - iv
• B. iii - ii - i - iv
• C. ii - i - iii - iv
• D. iii - i - ii - iv

Answer 1

The correct option is B iii - ii - i - iv

• Atmospheric nitrogen is unreactive. Hence, it cannot be used directly by the plants.
• Certain bacteria, blue green algae, etc, in the soil convert the atmospheric nitrogen into usable compounds.
• These compounds are absorbed by the plants to synthesise proteins. Herbivores obtain nitrogen by feeding on these plants, while carnivores obtain nitrogen from feeding either herbivores or other carnivores.
• Upon the death of organisms, certain bacteria, fungi, etc in the soil convert the nitrogenous wastes into usable forms. These are absorbed by the plants again.
• Also certain other bacteria convert some part into gaseous nitrogen which is again released into the atmosphere.