IGCSE›Cambridge IGCSE Biology›Mind mapsPhotosynthesisCambridge IGCSE Biology: Mind mapStudy pack PDFAlso for this subtopic:Revision notesFlashcardsSubtopic testCover factsWhat is it?Plants make carbohydrates using light energyHappens in chloroplastsChlorophyll transfers light to chemical energyNeeds light and chlorophyllEquationCarbon dioxide + water → glucose + oxygen6 COX2+6 HX2O→CX6HX12OX6+6 OX2\ce{6CO2 + 6H2O -> C6H12O6 + 6O2}6COX2+6HX2OCX6HX12OX6+6OX2Uses of glucoseStarch: energy storageCellulose: builds cell wallsRespiration: immediate energySucrose: transported in phloemNectar: attracts pollinating insectsPhotosynthesismaking glucoseCO₂H₂OO₂Mineral ionsNitrate makes amino acids, then proteins and enzymesMagnesium is needed to make chlorophyllMagnesium shortage: leaves yellow-greenLimiting factorsLight intensity: rate rises then plateausCO₂ concentration: often limiting at 0.04%Temperature: optimum about 25–35 °CAbove optimum, enzymes denatureIncreasing a non-limiting factor has no effectInvestigationsIodine turns blue-black with starchVariegated leaf: only green parts make starchSoda lime removes CO₂ from airIndicator: purple in light, yellow in darkExam tipsState light and chlorophyll as conditionsStarch is storage, cellulose is structureName independent, dependent, control variables