IB›IB Biology HL›Mind mapsA1.1 WaterIB Biology HL: Mind mapStudy pack PDFAlso for this subtopic:Revision notesFlashcardsSubtopic testCover factsPolarityOxygen pulls electrons harder: δ− O, δ+ HBonds are polar covalentHydrogen bond: δ+ H of one molecule to δ− O of anotherFirst cells originated in waterCohesion, adhesionCohesion: water–water attractionPulls water up xylem as an unbroken columnSurface tension lets pond skaters live on the surfaceAdhesion: water sticks to polar or charged surfacesCauses capillary action in soil and cell wallsSolventHydrophilic: ions and polar molecules dissolveMedium for metabolism and transport (plasma, sap)Hydrophobic molecules are insolubleUseful insoluble molecules: phospholipid tails, triglycerides, waxesWaterthe medium for lifeδ+δ−H-bondPhysical propertiesWater is about 800× denser than air: greater buoyancyHigher viscosity: more dragThermal conductivity about 24× air: heat lost fasterHigh specific heat capacity keeps temperatures stableRinged seal uses blubber for insulationOrigin and spaceEarth's water came from asteroidsEvidence: similar deuterium : hydrogen ratioRetained by strong gravityTemperatures low enough for vapour to condenseGoldilocks zone: liquid water possible on surfaceExam tipsLimit origin hypotheses to asteroidsRetention reasons: gravity and condensing temperaturesGoldilocks zone does not guarantee waterWater is necessary but not sufficient for life