This memory aid covers Memory Aids within Decomposition for GCSE Biology. Topic 4: Decomposition It is section 9 of 12 in this topic. Use it for quick recall, then test yourself straight afterwards so the memory aid becomes usable in an answer.
🧠 Memory Aids
Factors affecting decomposition rate — "TOMP":
- Temperature — warmer is faster (up to optimum ~37 °C); too hot = enzyme denaturation
- Oxygen — aerobic conditions needed for most decomposers; anaerobic = very slow
- Moisture — water needed for enzyme activity and decomposer survival
- pH — neutral optimum (~7); acid or alkaline conditions slow enzyme activity
How decomposers feed — "Secrete, Digest, Absorb" (SDA): Decomposers Secrete enzymes outside their body; enzymes Digest the organic material into small soluble molecules; the decomposer then Absorbs those molecules. Compare this to animals: animals ingest first, then digest internally.
Ideal compost conditions: Think of a compost heap needing the opposite of a fridge — warm (not cold), moist (not dry), aerated (not compacted). These conditions maximise decomposer activity and produce finished compost fastest.
Quick Check: A student sets up four identical pots, each containing the same mass of leaf litter and soil. The pots are kept at 5 °C, 20 °C, 37 °C, and 60 °C for four weeks. Predict and explain the results.
The 37 °C pot would show the most decomposition — this is near the enzyme optimum for most soil decomposers. The 20 °C pot would show intermediate decomposition. The 5 °C pot would show very little — low kinetic energy means few enzyme-substrate collisions and very slow metabolic rate. The 60 °C pot would also show very little — high temperature denatures decomposer enzymes, permanently altering the active site shape so they can no longer function, despite the high temperature.
Quick Check: A biogas generator produces methane from food waste under anaerobic conditions. A student suggests that adding oxygen would make it work more efficiently. Evaluate this suggestion.
The suggestion is incorrect. Biogas is produced by anaerobic bacteria (methanogens) that only function in the absence of oxygen. Adding oxygen would allow faster-growing aerobic bacteria to outcompete the methanogens. Aerobic bacteria produce CO₂ and water, not methane. The result would be faster decomposition of food waste but little or no methane production — defeating the purpose of the generator. Biogas generators are deliberately maintained under anaerobic conditions to favour methane-producing bacteria.
Quick Check: A farmer wants to maximise the rate of decomposition in a compost heap. Suggest three practical steps and explain the biological reason for each.
Step 1 — Turn the heap regularly: Most decomposers are aerobic and require oxygen for respiration. Turning the heap breaks up compacted material, allowing air to penetrate throughout and maintaining aerobic conditions. Step 2 — Keep the heap moist (add water if dry): Decomposer bacteria and fungi need water as a solvent for enzyme secretion and for metabolic reactions. Dry conditions inactivate or kill decomposers. Step 3 — Shred large items before adding: Smaller pieces have greater surface area exposed to enzyme contact, increasing the rate of breakdown by decomposers and detritivores.
Practice questions for Decomposition
Which organisms are the main decomposers?
Explain how temperature affects the rate of decomposition.