Match the following and choose the correct option.

	Column I		Column II
(a)	Earthworm	i.	Catabolism
(b)	Bacterial and fungal enzymes	ii.	Breaks down detritus into smaller particles
(c)	Accumulation of dark coloured amorphous substance	iii.	Detritivores
(d)	Fragmentation	iv.	Humus

	(a)	(b)	(c)	(d)
1.	iii	ii	iv	i
2.	iii	i	iv	ii
3.	ii	i	iv	iii
4.	ii	iii	iv	i

The breakdown of complex organic matter into simpler inorganic compounds such as carbon dioxide, water, and nutrients by decomposers is known as decomposition. Complex organic matters such as dead plant remains and dead remains of animals, including fecal matter, constitute the detritus, which is the raw material for decomposition.

The important steps in the process of decomposition are as follows:

1. Fragmentation: Detritivores (such as earthworms) break the detritus down into smaller particles. This process is referred to as fragmentation.
2. Leaching: By the process of leaching, water soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts.
3. Catabolism: Bacterial and fungal enzymes degrade the remaining detritus into simpler inorganic substances. This process is called catabolism.
4. Humification: Humification leads to accumulation of a dark coloured amorphous substance called humus. Humus is highly resistant to microbial action and undergoes decomposition at an extremely slow rate. Humus, being colloidal in nature, serves as a reservoir of nutrients.
5. Mineralisation: The humus is further degraded by some microbes and release of inorganic nutrients occurs by the process known as mineralisation.