Choose the correct option:
Statement I: Decomposition rate increases when detritus contains lignin and chitin.
Statement II: Humus formed during humification undergoes degradation by microbes, releasing inorganic nutrients through mineralisation.
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → I is false, while II is true
Statement I — False. Lignin (in wood) and chitin (in the outer covering of insects) are hard to break down. So detritus rich in lignin and chitin decomposes more slowly, not faster. Decomposition is quicker when detritus is rich in nitrogen and water-soluble substances such as sugars.
Statement II — True. Humification forms humus, a dark, colloidal substance that resists microbes and breaks down very slowly. Some microbes still degrade it, and the inorganic nutrients are released. This release is mineralisation, the last step of decomposition.
NCERT Extract:
Decomposition – “… 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. … In a particular climatic condition, decomposition rate is slower if detritus is rich in lignin and chitin, and quicker, if detritus is rich in nitrogen and water-soluble substances like sugars.”