LE 48-17Postsynaptic cellPresynaptic cellSynaptic vesiclescontainingneurotransmitterPresynaptic membraneVoltage-gatedCa2+ channelCa2+Postsynaptic membranePostsynaptic membraneNeuro-transmitterLigand-gatedion channelNa+K+Ligand-gatedion channelsSynaptic cleftLE 12-325 µmLE 42-21GillarchWaterflowOperculumGillarchBloodvesselOxygen-richbloodWater flowover lamellaeshowing % O2GillfilamentsO2Oxygen-poorbloodLamella15%40%70%100%90%60%30%5%Blood flowthrough capillariesin lamellaeshowing % O2Countercurrent exchangeEcosystemsThe biosphereOrganismsPopulationsCommunitiesCellsOrganellesMoleculesTissuesOrgans and organ systemsCell1 µmAtoms10 µm50 µmLE 2-4NucleusElectronsCloud of negativecharge (2 electrons)LE 2-9ElectronorbitalsElectron-shelldiagrams1s orbital 2s orbital Three 2p orbitals 1s, 2s, and 2p orbitalsFirst shell(maximum2 electrons)Second shell(maximum8 electrons)Neon, with twofilled shells(10 electrons)xzyLE 2-8FirstshellHydrogen1HLithium3LiSecondshellThirdshellSodium11NaBeryllium4BeMagnesium12MgBoron5BAluminum12AlSilicon14SiCarbon6CNitrogen7NPhosphorus15POxygen8OSulfur16SChlorine17ClFluorine9FNeon10NeArgon18ArHelium2HeAtomic numberElement symbolElectron-shelldiagramAtomic mass2He4.00LE 2-11bOxygen (O2)Name(molecularformula)Electron-shelldiagramStructuralformulaSpace-fillingmodelLE 2-11cWater (H2O)Name(molecularformula)Electron-shelldiagramStructuralformulaSpace-fillingmodelLE 2-11dMethane (CH4)Name(molecularformula)Electron-shelldiagramStructuralformulaSpace-fillingmodelLE 2-13NaSodium atom(an unchargedatom)ClChlorine atom(an unchargedatom)Na+Sodium ion(a cation)Cl–Chlorine ion(an anion)Sodium chloride (NaCl)LE 2-14Na+Cl–LE 2-12HOHH2Oδ+ δ+δ–LE 2-15δ–Water(H2O)Ammonia(NH3)Hydrogen bondδ+δ+δ–δ+δ+δ+Overview: The Molecule ThatSupports All of Life• Water is the biological medium on Earth• All living organisms require water more thanany other substance• Most cells are surrounded by water, and cellsthemselves are about 70-95% water• The abundance of water is the main reason theEarth is habitableThe polarity of water moleculesresults in hydrogen bonding• The water molecule is a polar molecule:The opposite ends have opposite charges• Polarity allows water molecules to formhydrogen bonds with each otherLE
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