Q.(a) Bring out the different steps involved in Mechanism of Decomposition. OR

(a) Decomposition proceeds through fragmentation, leaching, catabolism, humification and mineralisation; (b) ozone depletion raises UV-B exposure, causing skin cancer, eye damage, immune suppression, mutations, and reduced plant/phytoplankton productivity.

(a) Steps in the mechanism of decomposition

Decomposition is the breakdown of complex dead organic matter (detritus) into simpler inorganic substances by decomposers. It proceeds through the following steps:

1. Fragmentation: detritivores (e.g. earthworms, some insects) physically break down large pieces of detritus into smaller particles, increasing the surface area available for microbial attack.
2. Leaching: water percolating through the detritus dissolves and carries water-soluble inorganic nutrients down into the soil, where they may get precipitated as unavailable salts.
3. Catabolism: bacteria and fungi secrete extracellular enzymes that degrade the fragmented detritus biochemically into progressively simpler organic and inorganic compounds.
4. Humification: this leads to the accumulation of a dark-coloured, amorphous substance called humus, which is highly resistant to microbial breakdown and decomposes very slowly, acting as a reservoir of nutrients and improving soil structure and water-holding capacity.
5. Mineralisation: some microbes further degrade the humus, releasing inorganic nutrients (such as CO2, water, and mineral ions) back into the soil, making them available for uptake by producers once again.

These processes act simultaneously (not strictly one after another) and are influenced by factors such as the chemical composition of the detritus and climatic conditions (temperature and soil moisture); decomposition is faster in warm, moist conditions and slower in cold or very dry/anaerobic conditions.

(b) Effects of ozone depletion

The stratospheric ozone layer normally absorbs most of the sun's harmful ultraviolet-B (UV-B) radiation. Depletion of this ozone layer (largely due to chlorofluorocarbons and related pollutants) allows more UV-B radiation to reach the Earth's surface, with the following effects:

1. Human health: increased incidence of skin cancers (including melanoma), cataracts and other eye damage, and suppression of the immune system, making people more susceptible to infections. …