Read the given passage and answer the questions that follow:
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 mineralization.
How many of the following statements about humus are correct?
A. Humus is a dark coloured amorphous substance.
B. Humus is highly resistant to microbial action.
C. Being colloidal in nature, humus serves as a reservoir of nutrients.
D. Humus undergoes decomposition at an extremely fast rate.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Three
Humus forms during decomposition in the soil by humification. It is a dark, amorphous and colloidal material that holds nutrients and breaks down only very slowly.
A. Humus is a dark coloured amorphous substance. — True. Humification leads to a dark coloured amorphous substance called humus.
B. Humus is highly resistant to microbial action. — True. Microbes find it hard to break humus down.
C. Being colloidal in nature, humus serves as a reservoir of nutrients. — True. Its colloidal nature lets it hold nutrients.
D. Humus undergoes decomposition at an extremely fast rate. — False. Humus decomposes at an extremely slow rate, which is why it lasts in the soil.
So three statements (A, B and C) are correct.
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.”