Chapter 3

Chapter 3Chapter 3

Water and the Fitness of Water and the Fitness of the Environmentthe Environment

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22

Importance of waterImportance of water

•Overview: The Molecule That Overview: The Molecule That Supports All of LifeSupports All of Life

•Water is the Water is the biological mediumbiological medium here on Earthhere on Earth

•All living All living organisms require organisms require waterwater more than any other more than any other substancesubstance

33

Water FactsWater Facts• Three-quartersThree-quarters of the Earth’s of the Earth’s

surface is submerged in watersurface is submerged in water

• The abundance of water is the The abundance of water is the main reason the main reason the Earth is Earth is habitablehabitable

Figure 3.1

44

Water FactsWater Facts

• The The polarity of waterpolarity of water molecules molecules results in results in hydrogen bondinghydrogen bonding

• The water molecule is a The water molecule is a polar polar moleculemolecule

55

Water’s PolarityWater’s Polarity• The polarity of water moleculesThe polarity of water molecules

– Allows them to form Allows them to form hydrogen hydrogen bonds with each otherbonds with each other

– Contributes to the Contributes to the various various propertiesproperties water exhibits water exhibits

Hydrogenbonds

+

+

H

H+

+

–

–

– –

Figure 3.2

66

Properties of waterProperties of water

• Six Six emergent propertiesemergent properties of water of water contribute to Earth’s fitness for lifecontribute to Earth’s fitness for life

1.1.Cohesion/AdhesionCohesion/Adhesion

2.2.Surface tensionSurface tension

3.3.Temperature ModerationTemperature Moderation

4.4.High specific heatHigh specific heat

5.5.Evaporative coolingEvaporative cooling

6.6.Universal solventUniversal solvent

77

CohesionCohesion

• Water molecules exhibit cohesionWater molecules exhibit cohesion

• CohesionCohesion– Is the Is the bonding of a high percentage bonding of a high percentage

of the molecules to neighboring of the molecules to neighboring water moleculeswater molecules

– Is due to Is due to hydrogen bondinghydrogen bonding– Like moleculesLike molecules bonding to each bonding to each

other (water attracting other water other (water attracting other water molecules)molecules)

88

CohesionCohesion• CohesionCohesion

– Helps pull water up through the Helps pull water up through the microscopic vessels of plants microscopic vessels of plants (capillarity)(capillarity)

Water conducting cells

100 µmFigure 3.3

99

Surface TensionSurface Tension• Surface tensionSurface tension

– Is a measure of Is a measure of how hard it is to how hard it is to break the surfacebreak the surface of a liquid of a liquid

– Is Is related to cohesionrelated to cohesion

Figure 3.4

1010

Moderation of Moderation of TemperatureTemperature

• Water Water moderates air moderates air temperaturetemperature

• By absorbing heat from airBy absorbing heat from air that that is warmer and is warmer and releasing the releasing the stored heat to air that is coolerstored heat to air that is cooler

1111

Heat and TemperatureHeat and Temperature

• Kinetic energyKinetic energy– Is the energy of motionIs the energy of motion

• HeatHeat– Is a measure of the total amount of kinetic energy due to Is a measure of the total amount of kinetic energy due to

molecular motionmolecular motion• TemperatureTemperature

– Measures the intensity of heatMeasures the intensity of heat

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Water’s High Specific Water’s High Specific HeatHeat

• The specific heat of a substanceThe specific heat of a substance– Is the amount of Is the amount of heat that heat that

must be absorbed or lost for 1 must be absorbed or lost for 1 gram of that substance to gram of that substance to change its temperature by 1ºCchange its temperature by 1ºC

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Specific HeatSpecific Heat

• Water has a Water has a high specific heathigh specific heat which allows it to which allows it to minimize minimize temperature fluctuationstemperature fluctuations to to within limits that permit lifewithin limits that permit life– Heat is absorbedHeat is absorbed when when

hydrogen bonds breakhydrogen bonds break– Heat is releasedHeat is released when when

hydrogen bonds formhydrogen bonds form

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Evaporative CoolingEvaporative Cooling

• EvaporationEvaporation– Is the transformation of a substance from a liquid to a gasIs the transformation of a substance from a liquid to a gas– Requires energyRequires energy

• Heat of vaporizationHeat of vaporization– Is the quantity of heat a liquid must absorb for 1 gram of it to Is the quantity of heat a liquid must absorb for 1 gram of it to

be converted from a liquid to a gasbe converted from a liquid to a gas– 100100ooC steam has MORE HEAT than 100C steam has MORE HEAT than 100ooC boiling water (540 C boiling water (540

calories)calories)

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Evaporative CoolingEvaporative Cooling

•Is due to water’s Is due to water’s high heat of high heat of vaporizationvaporization

•Allows water to cool a surfaceAllows water to cool a surface

•Sweating cools the bodySweating cools the body as as heat energy from the body heat energy from the body changes sweat into a gaschanges sweat into a gas

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Insulation of Bodies of Insulation of Bodies of Water by Floating IceWater by Floating Ice

•Solid water, or Solid water, or iceice– Is Is less denseless dense than liquid than liquid waterwater

– FloatsFloats in liquid water in liquid water– Insulates water & Insulates water & organisms below ice layerorganisms below ice layer

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• The The hydrogen bondshydrogen bonds in ice in ice– Are more “ordered” than in liquid Are more “ordered” than in liquid

water, making ice less dense water, making ice less dense (crystal lattice)(crystal lattice)

Liquid water

Hydrogen bonds constantly break and re-form

IceHydrogen bonds are stable

Hydrogen bond

Figure 3.5

1818


•Since ice floats in waterSince ice floats in water– Life can exist under the frozen Life can exist under the frozen surfaces of lakes and polar surfaces of lakes and polar seasseas

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The Solvent of LifeThe Solvent of Life

•Water is a Water is a versatile solvent versatile solvent due to its polaritydue to its polarity

•It can form It can form aqueous solutionsaqueous solutions•Called the Called the universal solventuniversal solvent

because so many substances because so many substances dissolve in waterdissolve in water

2020

• The different regions of the polar The different regions of the polar water molecule can interact with water molecule can interact with ionic compounds called solutes ionic compounds called solutes and dissolveand dissolve them them

Negative

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 3.6

2121

• Water can also interact with Water can also interact with polar molecules such as proteinspolar molecules such as proteins

This 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 3.7

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Hydrophilic and Hydrophilic and Hydrophobic SubstancesHydrophobic Substances

•A A hydrophobichydrophobic substance substance– Does not have an affinity for waterDoes not have an affinity for water– NonpolarNonpolar– lipidslipids

•A A hydrophilichydrophilic substance substance– Has an affinity for waterHas an affinity for water– Polar or ionicPolar or ionic– Carbohydrates, saltsCarbohydrates, salts

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Solute Concentration in Solute Concentration in Aqueous SolutionsAqueous Solutions

•Since Since most biochemical reactions most biochemical reactions occur in water inside cells (aqueous occur in water inside cells (aqueous environments)environments)– It is important to learn to calculate It is important to learn to calculate the the concentration of solutesconcentration of solutes in an in an aqueous solutionaqueous solution

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Moles and MolarityMoles and Molarity

•A moleA mole– Represents an exact number of molecules Represents an exact number of molecules of a substance in a given massof a substance in a given mass

•MolarityMolarity– Is the number of moles of solute per liter Is the number of moles of solute per liter of solutionof solution

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Acids and BasesAcids and Bases

•Dissociation of water Dissociation of water moleculesmolecules leads to acidic and leads to acidic and basic conditions that affect basic conditions that affect living organismsliving organisms

•Organisms must maintain Organisms must maintain homeostasishomeostasis in the in the pH pH of of their internal and external their internal and external environmentsenvironments

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• Water can dissociate Into Water can dissociate Into hydronium ions (hydronium ions (H+ or HH+ or H33O+)O+) and and hydroxidehydroxide (OH-) ions (OH-) ions

• Changes in the concentration of Changes in the concentration of these ions Can have a great these ions Can have a great affect on pHaffect on pH in living organisms in living organisms

H

Hydroniumion (H3O+)

H

Hydroxideion (OH–)

H

H

H

H

H

H

+ –

+

Figure on p. 53 of water dissociating

Effects of Changes in pHEffects of Changes in pH

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Acids and BasesAcids and Bases

•An acidAn acid– Is any substance that increases the Is any substance that increases the hydrogen hydrogen ion concentrationion concentration of a solution of a solution

•A baseA base– Is any substance that Is any substance that reduces the hydrogen reduces the hydrogen ion concentrationion concentration of a solution (more OH- ions) of a solution (more OH- ions)

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The pH ScaleThe pH Scale• Scale goes from Scale goes from 0-14 with 7 neutral0-14 with 7 neutral• The pH of a solution Is determined by The pH of a solution Is determined by

the relative the relative concentration of hydrogen concentration of hydrogen ionsions

• Difference of Difference of 10X10X in hydrogen ion in hydrogen ion concentration between any two pH concentration between any two pH valuesvalues

• Acids have a higher number of H+ ions Acids have a higher number of H+ ions than a basethan a base

• AcidsAcids produce produce H+ ionH+ ion in solution in solution• BasesBases produce OH- ions in solution produce OH- ions in solution

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The pH scale and pH values The pH scale and pH values of various aqueous of various aqueous

solutionssolutions

Incr

easi

ngly

Aci

dic

[H+]

> [

OH

–]

Incr

easi

ngly

Bas

ic[H

+]

< [

OH

–]

Neutral[H+] = [OH–]

Oven cleaner

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

pH Scale

Battery acid

Digestive (stomach) juice, lemon juiceVinegar, beer, wine,colaTomato juice

Black coffee RainwaterUrine

Pure waterHuman blood

Seawater

Milk of magnesia

Household ammonia

Household bleach

Figure 3.8

3030

BuffersBuffers

• The The internal pHinternal pH of most living cells of most living cells– Must remain close to pH 7Must remain close to pH 7

• BuffersBuffers– Are substances that Are substances that minimize changes minimize changes

in the concentrations of hydrogen and in the concentrations of hydrogen and hydroxide ions in a solutionhydroxide ions in a solution

– Consist of an acid-base pair that Consist of an acid-base pair that reversibly combines with hydrogen ionsreversibly combines with hydrogen ions

– Made by organismsMade by organisms

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The Threat of Acid The Threat of Acid PrecipitationPrecipitation

•Acid precipitationAcid precipitation– Refers to Refers to rain, snow, or fograin, snow, or fog with a with a pH lower than pH 5.6pH lower than pH 5.6

– Is caused primarily by the Is caused primarily by the mixing of different pollutants mixing of different pollutants with water in the airwith water in the air

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•Acid precipitationAcid precipitation– Can damage life in Earth’s Can damage life in Earth’s ecosystemsecosystems

0

12

34

56

78

910

1112

1314

Moreacidic

Acidrain

Normalrain

Morebasic

Figure 3.9

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