Q- Each year a large amount of plant material, cellulose, is deposited on the surface of the planet earth. What are the natural processes this cellulose undergoes before yielding carbon dioxide, water and other end products? UPSC CSE Main 2022 GS Paper 3.
Answer- Cellulose is a polysaccharide that forms the main structural component of plant cell walls and is the most abundant organic compound on Earth. It consists of long chains of glucose units linked by β-1,4-glycosidic bonds. Cellulose is relatively resistant to degradation by most microorganisms due to its crystalline structure and association with lignin and hemicellulose. However, some microorganisms have evolved the ability to decompose cellulose by producing various enzymes called cellulases. The natural processes that cellulose undergoes before yielding carbon dioxide, water and other end products are:
Hydrolysis: Cellulases break down the β-1,4-glycosidic bonds in cellulose, releasing glucose molecules or shorter chains of glucose called cellobiose or cellodextrins. This process requires water as a reactant and releases energy as a product.
Fermentation: The glucose, cellobiose, or cellodextrins produced by hydrolysis are further metabolized by microorganisms through various pathways of fermentation. Depending on the type of microorganism and the environmental conditions, fermentation can produce different end products such as ethanol, lactic acid, acetic acid, hydrogen, methane, or carbon dioxide.
Oxidation: The end products of fermentation can be further oxidized by microorganisms or abiotic factors such as oxygen, light, or heat. Oxidation involves the removal of electrons from the organic molecules, releasing energy and producing carbon dioxide and water as the final end products.
The decomposition of cellulose is a key process in the carbon cycle and the soil ecosystem. It involves various microorganisms such as bacteria, fungi, actinomycetes, and protozoa that can degrade cellulose in different habitats such as soil, compost, rumen, termite gut, etc. It also involves various factors that affect the rate and extent of cellulose decomposition such as temperature, moisture, pH, oxygen availability, nutrient availability, etc. Cellulose decomposition contributes to the energy flow and nutrient cycling in the soil and also affects the soil structure and fertility.