Read the passage and answer the following questions:
The earthworm is often referred to as the farmer's 'friend' due to its beneficial role in the breakdown of complex organic matter and soil aeration. Similarly, decomposers play a crucial role in converting complex organic matter into inorganic substances like carbon dioxide, water, and nutrients through the process of decomposition. Detritus, consisting of dead plant remains (leaves, bark, flowers) and animal waste, serves as the raw material for decomposition. Decomposition involves several important steps: fragmentation, leaching, catabolism, humification, and mineralisation. Detritivores, like earthworms, contribute to the process by breaking down detritus into smaller particles, which is known as fragmentation. Through leaching, water-soluble inorganic nutrients percolate into the soil horizon and precipitate as less accessible salts. Bacterial and fungal enzymes play a vital role in degrading detritus into simpler inorganic substances, and this process is referred to as catabolism. It's essential to understand that all these steps in decomposition occur simultaneously on the detritus. Humification and mineralisation are significant processes occurring during decomposition in the soil. Humification involves the transformation of organic matter into stable, dark-coloured substances like humus. Mineralisation, on the other hand, refers to the conversion of organic nutrients into inorganic forms that plants can readily absorb.
Which of the following is not a characteristic of humus?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → It is further degraded by the process of humification
Humification and mineralisation take place during decomposition in the soil. Humification forms humus, a dark coloured amorphous substance that is highly resistant to microbial action and decomposes at an extremely slow rate. Humus is then broken down further by some microbes, which releases inorganic nutrients; this later step is mineralisation.
Option (1) Highly resistant to microbial action — A correct statement. Humus is highly resistant to microbial action, which is why it lasts long in the soil.
Option (2) Dark coloured amorphous substance — A correct statement. Humus is a dark coloured amorphous substance formed by humification.
Option (3) Undergoes decomposition at an extremely slow rate — A correct statement. Humus undergoes decomposition at an extremely slow rate.
Option (4) It is further degraded by the process of humification — An incorrect statement. Humification is the process that forms humus. The further breakdown of humus by microbes, with the release of inorganic nutrients, is called mineralisation.
NCERT Extract:
Decomposition – “… Humification and mineralisation occur during decomposition in the soil. Humification leads to accumulation of a dark coloured amorphous substance called humus that is highly resistant to microbial action and undergoes decomposition at an extremely slow rate. Being colloidal in nature it serves as a reservoir of nutrients. The humus is further degraded by some microbes and release of inorganic nutrients occur by the process known as mineralisation.”