Question

What is decomposition? Describe the decomposition cycle in a terrestrial ecosystem with a diagram.

Hint:

Order to remember: Fragmentation → Leaching → Catabolism → Humification → Mineralisation.

Answer 1

Step 1: Definition:
Decomposition is the process by which decomposers (mainly bacteria and fungi) break down complex organic matter present in dead plant and animal remains (detritus) into simpler inorganic substances, which are released back into the soil and can be reused by producers — this is essential for nutrient recycling.

Step 2: Fragmentation and leaching:
First, detritivores such as earthworms physically break the detritus into smaller particles (fragmentation), greatly increasing the surface area available for microbial attack. At the same time, water-soluble inorganic nutrients percolate down into the soil layers (leaching) and may get precipitated as unavailable salts.

Step 3: Catabolism and humification:
Bacterial and fungal enzymes then chemically degrade the detritus into simpler organic and inorganic compounds outside their cells (catabolism). This process, along with further breakdown, leads to the accumulation of a dark-coloured, amorphous substance called humus, which is highly resistant to microbial attack and decomposes only very slowly.

Step 4: Mineralisation:
Humus is further degraded by some microorganisms, in a process called mineralisation, which releases simple inorganic nutrients (such as CO2, water and mineral ions) that become available in the soil once again for uptake by plant roots.

Final Answer:
Decomposition proceeds through fragmentation → leaching → catabolism → humification → mineralisation, ultimately returning nutrients locked in dead organic matter back to the soil for reuse by plants; the rate is faster with nitrogen-rich, soft detritus and warm, moist, aerobic (oxygen-rich) conditions, and slower with hard, lignin/chitin-rich detritus or cold, dry, anaerobic conditions.