Match List I with List II: List I i. Decomposition ii. Detritus iii. Mineralisation iv. Humification List II (Definitions) a. Accumulation of dark coloured amorphous colloidal substance b. Release of inorganic nutrients by the activity of microbes in soil c. Breaking down of complex organic matter into inorganic substances d. Dead remains of plants and animals including fecal matter Choose the correct answer from the options given below:

i – c, ii – d, iii – b, iv – a

i – a, ii – b, iii – c, iv – d

i – d, ii – c, iii – a, iv – b

i – c, ii – b, iii – a, iv – d

Decomposition Process

சிதைவுறுதல் செயல்முறை

NCERT Class 12 · Ecosystem · 3 NEET questions

Nature does not tolerate waste. If decomposition stopped, the biosphere would suffocate under its own detritus within months. NEET aspirants often confuse Humification with Mineralisation; get this distinction wrong, and you lose 4 marks instantly.

The idea

Decomposition is the breakdown of detritus into inorganic raw materials. It proceeds in five steps: fragmentation, leaching, catabolism, humification, and mineralisation. Fragmentation by detritivores increases surface area. Catabolism involves extracellular enzymes secreted by fungi and bacteria. Humification creates dark, amorphous humus, while mineralisation releases inorganic nutrients back into the soil.

Why it matters

It is essential for nutrient cycling, ensuring that inorganic elements are returned to the soil for reuse by producers.

NEET lens

NEET focuses on the sequence of these five steps. Memorise that humification is resistant to microbial action, while mineralisation is the final step. Expect 'Assertion-Reason' questions regarding the impact of temperature and soil moisture on decomposition rates. High lignin and chitin content slow down the process; keep this correlation in mind.

Clinical significance

In the human gut, the microbiome performs a form of decomposition on undigested fiber. If this process fails, dysbiosis occurs, leading to malabsorption and systemic inflammation. Just as an ecosystem requires nutrient cycling, your body requires microbial breakdown to maintain homeostasis.

Introduction

Decomposers break down complex organic matter into inorganic substances like CO2, water and nutrients. The process is called decomposition.

Core concept

Raw material: detritus — dead plant remains such as leaves, bark and flowers, and dead remains of animals, including faecal matter. Steps (NCERT): fragmentation — detritivores (e.g. earthworm) break down detritus into smaller particles; leaching — water-soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts; catabolism — bacterial and fungal enzymes degrade detritus into simpler inorganic substances; humification — accumulation of a dark coloured amorphous substance called humus, highly resistant to microbial action, which undergoes decomposition at an extremely slow rate; being colloidal in nature it serves as a reservoir of nutrients; mineralisation — humus is further degraded by some microbes and release of inorganic nutrients occurs. Fragmentation, leaching and catabolism operate simultaneously on detritus.

Go deeper

Decomposition is largely an oxygen-requiring process. Its rate is controlled by the chemical composition of detritus and climatic factors: it is slower if detritus is rich in lignin and chitin, and quicker if rich in nitrogen and water-soluble substances like sugars. Warm and moist environments favour decomposition; low temperature and anaerobiosis inhibit it, leading to the build-up of organic materials.

From Class 10

Fallen leaves slowly rot and turn into dark soil. Worms, fungi and bacteria do this work — that is decomposition.