IGCSE›Oxford AQA IGCSE Biology›Mind mapsEnergy transferred in ecosystemsOxford AQA IGCSE Biology: Mind mapStudy pack PDFAlso for this subtopic:Revision notesFlashcardsSubtopic testCover factsEnergy in food chainsEnergy enters by photosynthesisPasses along trophic levelsOnly about 10% passes to the next levelFood webs are more realistic than chainsChains usually 3–5 levelsEnergy lostRespiration releases energy as heatEgestion: undigested foodExcretion: metabolic waste such as ureaEfficiency (HT)energy at higher levelenergy at lower level×100\frac{\text{energy at higher level}}{\text{energy at lower level}} \times 100energy at lower levelenergy at higher level×100Usually about 10%Write formula, substitute, then ×100Energy flowand nutrient cycles10%Carbon cyclePhotosynthesis removes CO₂Respiration returns CO₂Decomposition and combustion release CO₂Fossilisation stores carbon long termNitrogen cycle (HT)Nitrogen-fixing bacteria: N₂ → ammoniaNitrifying bacteria: ammonia → nitrate (aerobic)Denitrifying bacteria: nitrate → N₂ (anaerobic)Plants cannot use atmospheric N₂Water cycleEvaporation from water surfacesTranspiration from plantsCondensation forms cloudsPrecipitation then infiltrationDriven by the Sun