Ecosystem — BIOLOGY STD 12 Science — Question

Earthworms are farmers' friend because along with breaking down the complex organic substances in fields and gardens, they make the soil soft and porous. Similarly, decomposers help in breaking down complex organic matter into inorganic compounds like carbon dioxide, water and nutrients by the process of decomposition. Dead remains of plants like leaves, bark, twigs, flowers and dead remains of animals along with fecal matter form detritus which acts as raw material for decomposition. Fungi, bacteria and other micro-organisms and invertebrates like nematod, insects and earthworms play important role in the process of decomposition. The important steps in the process of decomposition are fragmentation, leaching, catabolism, humification and mineralization.
Detritivores like earthworms break down the detritus into small particles. This process is known as fragmentation. During the process of leaching water soluble inorganic nutrients move downward along with percolating water into soil layer. These inorganic nutrients are precipitated to form non-available forms. In catabolism bacterial and fungal enzymes breakdown the detritus into simple organic compounds and inorganic substances.
The process of humification and mineralization take place in the soil during decomposition. Humification results the accumulation of a dark coloured amorphous substance called humus. Humus is highly resistant to microbial actions and undergoes extremely slow decomposition. It serves as reservoir of nutrients as it is colloidal in nature. Humus is further degraded by some microbes and results in the release of inorganic nutrients by the process of mineralization.