IGCSE›Edexcel IGCSE Biology›Mind mapsThe Organism in the EnvironmentEdexcel IGCSE Biology: Mind mapStudy pack PDFAlso for this subtopic:Revision notesFlashcardsSubtopic testCover factsKey termsPopulation: one species in a habitatCommunity: all species interacting in a habitatHabitat = where an organism livesEcosystem = community plus abiotic environmentQuadratsSquare frame of known areaPlace randomly to avoid biasCount individuals, find the mean per quadratMean × (habitat area ÷ quadrat area) = populationMore quadrats give a more reliable estimateBiodiversityBiodiversity = variety of species in an areaHigh when many species in even numbersRecord every species in random quadratsA transect shows how distribution changesEnvironmentorganisms and habitatsAbiotic factorsNon-living physical and chemical conditionsLight intensity limits photosynthesisTemperature affects enzyme reactionsWater and pH limit where species liveOxygen and CO2 matter in aquatic habitatsBiotic factorsLiving influences on a populationPredation: more predators, fewer preyCompetition for food, light, space or matesDisease spreads at high densityFood availability limits consumer numbersExam tipsChoosing nice-looking patches biases the estimateDrought cuts plants, then herbivore foodAbiotic and biotic factors interact