IGCSE›Cambridge IGCSE Biology›Mind mapsDiffusionCambridge IGCSE Biology: Mind mapStudy pack PDFAlso for this subtopic:Revision notesFlashcardsSubtopic testCover factsWhat is it?Net movement of particles from high to low concentrationDown a concentration gradientCaused by random kinetic movementPassive: no ATP neededStops net movement at equilibriumAcross membranesMembrane is partially permeableSmall molecules pass: O₂, CO₂Large molecules (proteins, starch) cannotWater moves by osmosisWhy it mattersO₂ diffuses into respiring cellsCO₂ diffuses out, toxic if it builds upGlucose diffuses from gut into bloodUrea diffuses out for excretionDiffusionpassive movementO₂CO₂Rate factorsSteeper concentration gradient = fasterLarger surface area = fasterHigher temperature = faster, more kinetic energyShorter distance = fasterExchange surfacesLarge surface area: alveoli, villi, gillsThin walls, one cell thickGood blood supply keeps gradient steepVentilation refreshes the gradientExam tipsSay random movement, not 'seeking equilibrium'Name the process it serves, e.g. respirationExplain each factor's mechanism