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? (Answer in 150 words)

Cellulose enters the detritus pathway after plant death. Its conversion is a sequence of physical breakdown, microbial digestion and chemical mineralisation.

Natural sequence

• Litter is fragmented by weathering and detritivores, increasing surface area and mixing organic matter with soil.
• Fungi and bacteria secrete cellulase enzymes that hydrolyse cellulose into sugars such as glucose.
• Aerobic decomposers oxidise sugars through respiration, releasing carbon dioxide, water and energy.
• Under waterlogged or oxygen-poor conditions, anaerobic microbes produce methane, carbon dioxide, organic acids and other products.
• Humification converts part of the material into relatively stable soil organic matter, while mineralisation releases nutrients such as nitrogen and phosphorus.

Factors affecting rate

• Temperature, moisture, oxygen, pH, litter quality, lignin content and decomposer diversity control decomposition.
• Warm, moist, oxygenated environments generally accelerate aerobic decay, whereas cold, dry or anaerobic conditions slow it or alter end products.

Ecological significance

• The process recycles carbon and nutrients, sustains soil fertility and links terrestrial productivity with atmospheric composition.

Cellulase; detritus; aerobic respiration; anaerobic decomposition; humification; mineralisation; carbon cycle.