This how it works covers Why Conditions Affect the Rate of Decomposition within Decomposition for GCSE Biology. Topic 4: Decomposition It is section 6 of 12 in this topic. Use this how it works to connect the idea to the wider topic before moving on to questions and flashcards.
⚙️ Why Conditions Affect the Rate of Decomposition
Decomposition is carried out by microorganisms — mainly bacteria and fungi — which secrete enzymes onto dead organic material, break it down externally into small soluble molecules, and absorb those molecules as nutrients. Because the process depends entirely on enzyme activity, any factor that affects enzyme function will affect the rate of decomposition.
Temperature: Increasing temperature increases the kinetic energy of enzyme and substrate molecules, making collisions more frequent and reactions faster. However, above the optimum temperature (approximately 37 °C for most soil decomposers), enzymes become denatured — the active site changes shape and the enzyme can no longer catalyse reactions. Very cold conditions slow enzyme activity dramatically, which is why food stored in a freezer does not rot.
Oxygen: Most decomposer bacteria and fungi are aerobic — they require oxygen for respiration to release energy for enzyme production, growth, and reproduction. In oxygen-poor (anaerobic) conditions, only anaerobic decomposers can function, and these are less efficient. This is why waterlogged or compacted soil decomposes organic material far more slowly than aerated soil — and why peat (formed in anaerobic bogs) preserves organic matter for thousands of years.
Moisture: Water is needed as a solvent for enzyme secretion and nutrient absorption, and for the decomposers' own metabolic reactions. Very dry conditions kill or inactivate many decomposers. This principle is used in composting — gardeners turn compost heaps to introduce oxygen and add water to maintain optimal conditions.
pH: Enzymes have an optimal pH, typically around neutral (pH 7) for soil decomposers. Highly acidic or alkaline conditions alter the charge distribution on the enzyme's active site, changing its shape and reducing its effectiveness. Sphagnum moss in peat bogs produces acidic conditions that inhibit decomposer activity, further slowing carbon release.
Practice questions for Decomposition
Which organisms are the main decomposers?
Explain how temperature affects the rate of decomposition.