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.
Decomposition is largely a process that requires:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Oxygen
Decomposition is carried out by soil microbes and detritivores, and most of them need oxygen for their activities. That is why NCERT calls decomposition largely an oxygen-requiring process, and why anaerobiosis (lack of oxygen) inhibits it.
Option (1) Calcium — Incorrect. Calcium is one of the mineral nutrients that may be released from detritus; it is not what the process requires.
Option (2) Phosphorus — Incorrect. Phosphorus too is a nutrient released during mineralisation, not a requirement of decomposition.
Option (3) Oxygen — Correct. Decomposition is largely an oxygen-requiring process. Without oxygen it is inhibited and organic matter builds up.
Option (4) Carbon dioxide — Incorrect. Carbon dioxide is one of the products of decomposition, along with water and nutrients.
NCERT Extract:
Decomposition – “… Similarly, decomposers break down complex organic matter into inorganic substances like carbon dioxide, water and nutrients and the process is called decomposition.”
Decomposition – “Decomposition is largely an oxygen-requiring process. … Warm and moist environment favour decomposition whereas low temperature and anaerobiosis inhibit decomposition resulting in build up of organic materials.”