Define decomposition. Explain any four steps of decomposition in correct sequence.

Answer: Decomposition is the process by which decomposers (mainly bacteria and fungi, helped by detritivores) break down complex organic matter of dead plants and animals (detritus) into simple inorganic substances such as CO₂, water and nutrients.

Steps in sequence:

1. Fragmentation: detritivores such as earthworms break detritus into smaller particles, increasing the surface area.
2. Leaching: water-soluble inorganic nutrients percolate down into the soil and get precipitated as unavailable salts.
3. Catabolism: bacterial and fungal enzymes degrade the detritus into simpler inorganic substances.
4. Humification: formation of humus, a dark, amorphous, colloidal substance rich in cellulose and lignin that is highly resistant to microbial action and decomposes very slowly; it serves as a reservoir of nutrients.
5. Mineralisation: humus is further degraded by microbes and inorganic nutrients are released into the soil.