Q. Each year a large amount of plant material, cellulose, is deposited on the surface of Planet Earth. What are the natural processes this cellulose undergoes before yielding carbon dioxide, water and other end products ?

Model Answer: 

Natural Processes of Cellulose Decomposition on Earth

Cellulose, the primary component of plant cell walls, is deposited in large quantities on Earth’s surface annually. Its decomposition is a crucial part of the carbon cycle. The natural processes breaking down cellulose into carbon dioxide, water, and other end products include:

Microbial decomposition:
• Bacteria and fungi play a vital role in breaking down cellulose.
• They secrete enzymes like cellulase that catalyze the breakdown process.
• This occurs in various environments, from forest floors to aquatic ecosystems.

Chemical decomposition:
• Environmental factors contribute to cellulose breakdown:
– Sunlight causes photodegradation (e.g., bleaching of fallen leaves)
– Oxygen facilitates oxidation
– Water enables hydrolysis, breaking cellulose into simpler compounds
• These processes work in tandem with microbial activity, accelerating decomposition.

Physical decomposition:
• Temperature fluctuations, particularly freeze-thaw cycles, weaken cellulose structure.
• Mechanical weathering (e.g., wind erosion, animal trampling) fragments cellulose, increasing surface area for other decomposition processes.

The main end products of cellulose decomposition are:
1. Carbon dioxide (CO2)
2. Water (H2O)
3. In anaerobic conditions, methane (CH4) may also be produced
4. Intermediate products include simple sugars and organic acids

These processes are essential for nutrient cycling and soil formation. In forests, for instance, leaf litter decomposition enriches the soil. In aquatic systems, decomposing plant material supports food webs.

Conclusion: Cellulose decomposition, through microbial, chemical, and physical processes, is fundamental to Earth’s carbon cycle and ecosystem functioning.