Bài giảng Biology - Chapter 3: Water and the Fitness of the Environment

Chapter 3Water and the Fitness of the EnvironmentOverview: The Molecule That Supports All of LifeWater is the biological medium here on EarthAll living organisms require water more than any other substanceThree-quarters of the Earth’s surface is submerged in waterThe abundance of water is the main reason the Earth is habitableFigure 3.1Concept 3.1: The polarity of water molecules results in hydrogen bondingThe water molecule is a polar moleculeThe polarity of water moleculesAllows them to form hydrogen bonds with each otherContributes to the various properties water exhibitsHydrogenbonds++HH++ – – – –Figure 3.2Concept 3.2: Four emergent properties of water contribute to Earth’s fitness for lifeCohesionWater molecules exhibit cohesionCohesionIs the bonding of a high percentage of the molecules to neighboring moleculesIs due to hydrogen bondingCohesionHelps pull water up through the microscopic vessels of plantsWater conducting cells100 µmFigure 3.3Surface tensionIs a measure of how hard it is to break the surface of a liquidIs related to cohesionFigure 3.4Moderation of TemperatureWater moderates air temperatureBy absorbing heat from air that is warmer and releasing the stored heat to air that is coolerHeat and TemperatureKinetic energyIs the energy of motionHeatIs a measure of the total amount of kinetic energy due to molecular motionTemperatureMeasures the intensity of heatWater’s High Specific HeatThe specific heat of a substanceIs the amount of heat that must be absorbed or lost for 1 gram of that substance to change its temperature by 1ºCWater has a high specific heat, which allows it to minimize temperature fluctuations to within limits that permit lifeHeat is absorbed when hydrogen bonds breakHeat is released when hydrogen bonds formEvaporative CoolingEvaporationIs the transformation of a substance from a liquid to a gasHeat of vaporizationIs the quantity of heat a liquid must absorb for 1 gram of it to be converted from a liquid to a gasEvaporative coolingIs due to water’s high heat of vaporizationAllows water to cool a surfaceInsulation of Bodies of Water by Floating IceSolid water, or iceIs less dense than liquid waterFloats in liquid waterThe hydrogen bonds in iceAre more “ordered” than in liquid water, making ice less denseLiquid waterHydrogen bonds constantly break and re-formIceHydrogen bonds are stableHydrogen bondFigure 3.5Since ice floats in waterLife can exist under the frozen surfaces of lakes and polar seasThe Solvent of LifeWater is a versatile solvent due to its polarityIt can form aqueous solutionsThe different regions of the polar water molecule can interact with ionic compounds called solutes and dissolve themNegative oxygen regions of polar water molecules are attracted to sodium cations (Na+).++++Cl –––––Na+Positive hydrogen regions of water molecules cling to chloride anions (Cl–).++++––––––Na+Cl–Figure 3.6Water can also interact with polar molecules such as proteinsThis oxygen is attracted to a slight positive charge on the lysozyme molecule.This oxygen is attracted to a slight negative charge on the lysozyme molecule.(a) Lysozyme molecule  in a nonaqueous  environment(b) Lysozyme molecule (purple)  in an aqueous environment  such as tears or saliva(c) Ionic and polar regions on the protein’s  Surface attract water molecules. +–Figure 3.7Hydrophilic and Hydrophobic SubstancesA hydrophilic substanceHas an affinity for waterA hydrophobic substanceDoes not have an affinity for waterSolute Concentration in Aqueous SolutionsSince most biochemical reactions occur in waterIt is important to learn to calculate the concentration of solutes in an aqueous solutionA moleRepresents an exact number of molecules of a substance in a given massMolarityIs the number of moles of solute per liter of solutionConcept 3.3: Dissociation of water molecules leads to acidic and basic conditions that affect living organismsWater can dissociateInto hydronium ions and hydroxide ionsChanges in the concentration of these ionsCan have a great affect on living organismsHHydroniumion (H3O+)HHydroxideion (OH–)HHHHHH+–+Figure on p. 53 of water dissociatingEffects of Changes in pHAcids and BasesAn acidIs any substance that increases the hydrogen ion concentration of a solutionA baseIs any substance that reduces the hydrogen ion concentration of a solutionThe pH ScaleThe pH of a solutionIs determined by the relative concentration of hydrogen ionsIs low in an acidIs high in a baseThe pH scale and pH values of various aqueous solutionsIncreasingly Acidic[H+] > [OH–]Increasingly Basic[H+] < [OH–]Neutral[H+] = [OH–]Oven cleaner 0 1 2 3 4 5 6 7 8 91011121314pH ScaleBattery acidDigestive (stomach) juice, lemon juiceVinegar, beer, wine,colaTomato juiceBlack coffee RainwaterUrinePure waterHuman bloodSeawaterMilk of magnesiaHousehold ammoniaHousehold bleachFigure 3.8BuffersThe internal pH of most living cellsMust remain close to pH 7BuffersAre substances that minimize changes in the concentrations of hydrogen and hydroxide ions in a solutionConsist of an acid-base pair that reversibly combines with hydrogen ionsThe Threat of Acid PrecipitationAcid precipitationRefers to rain, snow, or fog with a pH lower than pH 5.6Is caused primarily by the mixing of different pollutants with water in the airAcid precipitationCan damage life in Earth’s ecosystems01234567891011121314MoreacidicAcidrainNormalrainMorebasicFigure 3.9