Biology · Ecosystems · NEET
Slower. This is the most tested point for NEET. Lignin (in wood) and chitin (in fungal walls and insect parts) are hard for microbes to break down, so detritus rich in them decomposes slowly. Detritus rich in nitrogen and water-soluble sugars decomposes fast. NEET 2022 tested exactly this and marked the statement 'decomposition is faster if rich in lignin and chitin' as INCORRECT.
Microbes (bacteria and fungi) are more active when it is warm and there is enough water. Warmth speeds up their enzymes, and moisture keeps them alive and lets nutrients move. So decomposition is fast in warm, moist soil (like a tropical forest floor) and slow in cold or dry places.
Decomposition is largely an OXYGEN-requiring (aerobic) process. Microbes need oxygen to break down detritus. This is why waterlogged (flooded) soil slows decomposition down — water fills the air spaces and cuts off oxygen. Remember: no oxygen = slow decomposition.
Waterlogging pushes air out of the soil, so oxygen becomes low or absent (anaerobic). Since decomposition is an aerobic process, the microbes cannot work well without oxygen, so the rate drops. This is why dead matter piles up in swamps and bogs.
1) The chemical quality of the detritus (nitrogen and sugars speed it up; lignin and chitin slow it down). 2) The climatic factors — temperature and soil moisture (warm and moist speeds it up; cold and dry slows it down). Oxygen availability also matters because the process is aerobic.
Given below are two statements: Statement I: Decomposition is a process in which the detritus is degraded into simpler substances by microbes. Statement II: Decomposition is faster if the detritus is rich in lignin and chitin. In the light of the above statements, choose the correct answer:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Detritus rich in nitrogen and water-soluble sugars decomposes fastest, for example soft green leaves. Woody detritus rich in lignin decomposes slowest.
Yes. Warm temperatures speed up microbial activity and make decomposition faster. Low temperature slows it down, which is why decomposition is slow in cold regions.
Decomposition is largely an aerobic process. The microbes that break down detritus use oxygen, so low-oxygen (anaerobic) conditions like waterlogging slow the process.
Yes. Nitrogen-rich, sugary detritus is easy for microbes to break down, so it rots fast. Woody twigs are rich in lignin, which is hard to break down, so they rot slowly.
Cold temperature, waterlogged (no oxygen) soil, and detritus rich in lignin and chitin together give the slowest decomposition.
