Question

Which one of the following is incorrect with respect to the decomposition process?

• A. Humification - leads to the accumulation of a dark coloured humus which undergoes microbial action at a very fast rate.
• B. Leaching - water soluble inorganic nutrients leach to the upper layers of soil by percolation of water into soil particles.
• C. Catabolism - last step of decomposition carried out by saprophytic organisms.
• D. Fragmentation - Carried out by organisms such as earthworms.

Answer 1

The correct option is A Humification - leads to the accumulation of a dark coloured humus which undergoes microbial action at a very fast rate.

Three main types of processes occur during decomposition.
First up is fragmentation in which dead plant parts and animal remains, called detritus, are processed by small invertebrate animals like earthworms and termites, called detritivores, They physically break down the organic matter into smaller fragments. Leaching is the second step, where parts of soluble substances present in the fragmented and decomposing detritus get leached to the upper layers of soil by percolation of water into soil particles. The final step is catabolism which is mainly carried out by saprotrophic bacteria and fungi which secrete digestive enzymes into the fragmented detritus, where the complex organic compounds are broken down to simpler compounds and inorganic substances. The rate of catabolism of different complex substances is different. It is further divided into two steps - humification and mineralisation. Humification is the process by which simplified detritus gets converted into a dark coloured formless substance that is rich in cellulose, lignin, tannins, resin, etc. This substance is known as humus. Its specific character is that it is highly resistant to microbial action and so,it undergoes extremely slow decomposition. Mineralisation is a very important process, because it releases inorganic substances like carbon dioxide, water, and minerals from the remains of organic matter.