Read the following passage carefully and answer the given questions.
The earthworm is referred to as the farmer's friend. This is because they help in the breakdown of complex organic matter as well as in loosening of soil. Similarly, decomposers break down complex organic matter into inorganic substances like carbon dioxide, water and nutrients and the process is called decomposition. Dead plant remains such as leaves, bark, flowers and dead remains of animals, including fecal matter, constitute detritus, which is the raw material for decomposition. Some of the steps in the process of decomposition are fragmentation, catabolism, leaching, humification etc.
Process of accumulation of dark coloured amorphous substance is called:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Humification
Option (1) Mineralisation — Incorrect. Mineralisation comes after humification. It breaks humus down and releases inorganic nutrients, so it uses up the dark substance instead of building it up.
Option (2) Fragmentation — Incorrect. In fragmentation, detritivores such as earthworms break detritus into smaller particles. The pieces are smaller, but no new dark substance is formed.
Option (3) Leaching — Incorrect. In leaching, water-soluble inorganic nutrients go down into the soil and settle as unavailable salts. It moves nutrients; it does not form humus.
Option (4) Humification — Correct. The dark coloured amorphous substance is humus. Amorphous means it has no definite shape. The process that builds it up in the soil is humification.
Note: This passage is taken from NCERT as it is. Most CUET (UG) questions come straight from NCERT, so study the book line by line, including figures and their titles.
NCERT Extract:
Decomposition – “… Bacterial and fungal enzymes degrade detritus into simpler inorganic substances. This process is called as catabolism. It is important to note that all the above steps in decomposition operate simultaneously on the detritus (Figure 12.1). 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.”
