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Ecosystem — BIOLOGY STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 ScienceBIOLOGYEcosystem4 Marks
Question
Define decomposition and describe the processes and products of decomposition.###Describe factor affecting decomposition.
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Answer

Decomposition :
→ Break down complex organic matter into inorganic substances like carbon dioxide, water and nutrients and the process is called decomposition.
→ Dead plant remains such as leaves, bark, flowers and dead remains of animals, including feacal matter, constitute detritus, which is the raw material for decomposition.
Important steps for decomposition :
→ The important steps in the process of decomposition are fragmentation, leaching, catabolism, humification and mineralisation.
Fragmentation :
→ Detritivores (e.g., earthworm) break down detritus into smaller particles. This process is called fragmentation.
Leaching :
→ By the process of 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. This process is called as catabolism.
Humification :
→ 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.
Mineralisation :
→ The humus is further degraded by some microbes and release of inorganic nutrients occur by the process known as mineralisation.
Factors affecting decomposition :
→ Decomposition is largely an oxygen- requiring process.
→ The rate of decomposition is controlled by chemical composition of detritus and climatic factors.
→ In a particular climatic condition, decomposition rate is slower if detritus is rich in lignin and chitin.
→ Decomposition rate is quicker, if detritus is rich in nitrogen and water-soluble substances like sugars.
→ Temperature and soil moisture are the most important climatic factors that regulate decomposition through their effects on the activities of soil microbes.
→ Warm and moist environment favour decomposition, whereas low temperature and anaerobiosis inhibit decomposition resulting in build up of organic materials.

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