Cambridge IGCSE·Co-ordinated Sciences 0654·Biology
Organisms Environment
Key knowledge — Organisms Environment
Formulas & equations
Energy efficiency between trophic levels ≈ 10% (only ~10% of energy passes to next level)Population change = (births + immigration) − (deaths + emigration)
Key facts & rules
- Producer: photosynthetic organism (plant/algae) — first trophic level.
- Consumer: organism that eats other organisms.
- Decomposer: breaks down dead organic matter (bacteria, fungi) — recycles nutrients.
- Food chain: linear energy flow. Food web: interconnected food chains.
- Carbon cycle: photosynthesis removes CO₂; respiration, decomposition, combustion release CO₂.
- Nitrogen cycle: nitrogen fixation (bacteria) → nitrification → assimilation → denitrification.
- Limiting factors for population: food, water, space, predation, disease.
- Biodiversity: variety of species in an ecosystem — higher = more stable.
IGCSE Biology — Organisms & environment
1851 Cambridge IGCSE 0654 biology past paper questions on organisms & environment, organised by subtopic. Pick a subtopic to start practising.
About organisms & environment on IGCSE 0654
Food chains and webs, energy flow, the carbon and nitrogen cycles, populations and ecosystems.