Explain the processes involved in the nitrogen cycle. Class 9

Explain the processes involved in the nitrogen cycle. Class 9

Question 1.

Explain the processes involved in the nitrogen cycle. How would life on Earth be affected if nitrogen were not cycled? Class 9

Answer:

The movement of nitrogen between air, soil, water and organisms is called the nitrogen cycle. Nitrogen is essential for synthesis of proteins and nucleic acids.

Processes Involved:

(a) Nitrogen Fixation:

1. Bacteria like Rhizobium (in legume roots) and Azotobacter (in soil) convert atmospheric N₂ into ammonia (NH₃).
2. Lightning also fixes small amounts of nitrogen.

(b) Nitrification:

1. Nitrosomonas converts ammonia into nitrite (NO_2-).
2. Nitrobacter converts nitrite into nitrate (NO_3-) which plants can absorb.

(c) Assimilation:

1. Plants absorb nitrates and synthesize proteins and nucleic acids.
2. Animals get nitrogen by eating plants or other animals.

(d) Ammonification:

1. When organisms die, decomposers like bacteria and fungi break down organic matter and return ammonia to the soil.

(e) Denitrification:

1. Pseudomonas bacteria convert nitrates back into N₂ gas, returning it to the atmosphere and completing the cycle.

If nitrogen were not cycled:

• Plants would not get nitrates from soil and could not make proteins — they would die.

• Animals depending on plants would have no food and would perish.

• Soil would lose all fertility, collapsing agriculture worldwide.

• Dead organic matter would accumulate as decomposition would stop.

• Ultimately all ecosystems would collapse. Conclusion: The nitrogen cycle is essential for soil fertility, plant growth and animal survival. Without it, life on Earth would cease to exist.