11

Chapter 3Chapter 3

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

22

Importance of waterImportance of water

• Overview: The Molecule That Overview: The Molecule That Supports All of Life on Planet EarthSupports All of Life on Planet Earth

• In one way or another, all life forms In one way or another, all life forms are dependent on water for life are dependent on water for life processes to occur.processes to occur.

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

• All living All living organisms require waterorganisms require water more than any other substancemore than any other substance

33

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

is submerged in wateris submerged in water

• The abundance of water is the main The abundance of water is the main reason the reason the Earth is habitableEarth is habitable

Figure 3.1

44

Water FactsWater Facts

• The The polarity of waterpolarity of water molecules molecules results in hydrogen bondingresults in hydrogen 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 bonds hydrogen bonds with each otherwith each other

– Contributes to the Contributes to the various propertiesvarious properties water exhibitswater exhibits

Hydrogenbonds

+

+

H

H+

+

–

–

– –

Figure 3.2

66

Properties of waterProperties of water

• Four Four emergent propertiesemergent properties of water of water contribute to Earth’s fitness for lifecontribute to Earth’s fitness for life– Cohesion / AdhesionCohesion / Adhesion– Surface TensionSurface Tension– Thermal PropertiesThermal Properties– Universal SolventUniversal Solvent

77

Cohesion / AdhesionCohesion / Adhesion

• Water molecules exhibit cohesionWater molecules exhibit cohesion

• CohesionCohesion– Is the bonding of molecules to neighboring Is the bonding of molecules to neighboring

moleculesmolecules– Is due to hydrogen bondingIs due to hydrogen bonding– Like molecules bonding to each other (water Like molecules bonding to each other (water

attracting other water molecules)attracting other water molecules)

• Adhesion – is the act of two different substances Adhesion – is the act of two different substances “sticking” to each other. Example: water will “adhere” “sticking” to each other. Example: water will “adhere” to the sides of a test tube or the “vein” (xylem) cells of to the sides of a test tube or the “vein” (xylem) cells of a planta plant

88

• CohesionCohesion– Helps pull water up through the Helps pull water up through the

microscopic vessels of plantsmicroscopic vessels of plants

Water conducting cells (xylem)

100 µmFigure 3.3

99

Surface TensionSurface Tension• Surface tensionSurface tension

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

– Is related to cohesionIs related to cohesion

Figure 3.4

1010

Thermal PropertiesThermal Properties

Moderation of Moderation of TemperatureTemperature• Water Water moderates air temperaturemoderates air temperature

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

1111

Thermal PropertiesThermal Properties

Heat and TemperatureHeat and Temperature• Kinetic energy Kinetic energy is the energy of motionis the energy of motion

• HeatHeat– Is a form of energyIs a form of energy– Is a measure of the total amount of kinetic Is a measure of the total amount of kinetic

energy due to molecular motionenergy due to molecular motion– Is the lowest form of energyIs the lowest form of energy– As energy is converted from one form to another As energy is converted from one form to another

it will always end up as heat – it will always end up as heat – EntropyEntropy– Maintaining “Life” is about preventing our body Maintaining “Life” is about preventing our body

systems from reaching a state of “entropy” – systems from reaching a state of “entropy” – because there is no other energy transformation because there is no other energy transformation that can take place – the flow stops!that can take place – the flow stops!

• Temperature Temperature measures the intensity (amount) of measures the intensity (amount) of heatheat

1212

Thermal Properties Thermal Properties

Water’s High Specific HeatWater’s High Specific Heat

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

absorbed or lost for 1 gram of that absorbed or lost for 1 gram of that substance to change its temperature by substance to change its temperature by 1ºC1ºC

1313

Thermal Properties Thermal Properties

Specific HeatSpecific Heat

• Water has a high specific heat (1), Water has a high specific heat (1), which allows it to minimize which allows it to minimize temperature fluctuations to within temperature fluctuations to within limits that permit lifelimits that permit life– Heat is absorbed when hydrogen bonds Heat is absorbed when hydrogen bonds

breakbreak– Heat is released when hydrogen bonds Heat is released when hydrogen bonds

formform

1414

Thermal Properties Thermal Properties

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 Is the quantity of heat a liquid must absorb for 1 gram of it

to be converted from a liquid to a gasto be converted from a liquid to a gas

1515

Thermal Properties Thermal Properties

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 body as heat Sweating cools the body as heat energy from the body changes energy from the body changes sweat into a gas and allows heat to sweat into a gas and allows heat to escape (entropy)escape (entropy)

1616

Thermal Properties Thermal Properties

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

• Solid water, or iceSolid water, or ice– Is less dense than liquid waterIs less dense than liquid water– Floats in liquid waterFloats in liquid water

1717

Thermal Properties Thermal Properties

Insulation of Bodies of Insulation of Bodies of Water by Floating Ice Water by Floating Ice• The hydrogen bonds in ice are more “ordered” The hydrogen bonds in ice are more “ordered”

than in liquid water, making ice less densethan in liquid water, making ice less dense

Liquid water

Hydrogen bonds constantly break and re-form

Ice

Hydrogen bonds are stable

Figure 3.5

1818

Thermal Properties Thermal Properties

Insulation of Bodies of Water by Floating IceInsulation of Bodies of Water by Floating Ice

• Since ice floats in water life can exist Since ice floats in water life can exist under the frozen surfaces of lakes under the frozen surfaces of lakes and polar seasand polar seas

1919

The Solvent of LifeThe Solvent of Life

• Water is a versatile solvent due to its Water is a versatile solvent due to its polaritypolarity

• It can form It can form aqueous solutionsaqueous solutions

• Called the Called the universal solventuniversal solvent because because so many substances dissolve in so many substances dissolve in waterwater

2020

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

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

Lysozymes are a group of enzymes which damage bacterial cell walls by destroying the 1,4-beta-linkages between N-acetylmuramic acid and N-acetyl-D-glucosamine residues in peptidoglycan and between N-acetyl-D-glucosamine residues in chitodextrins. It is abundant in a number of secretions, such as tears, saliva, and mucus. Large amounts of lysozymes are also found in egg whites.

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

2121

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

2222

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

• A A hydrophilichydrophilic substance substance– Has an affinity for waterHas an affinity for water

2323

Solute Concentration in Solute Concentration in Aqueous SolutionsAqueous Solutions

• Since most biochemical reactions Since most biochemical reactions occur in wateroccur in water– It is important to learn to calculate the It is important to learn to calculate the

concentration of solutes in an aqueous concentration of solutes in an aqueous solutionsolution

2424

Moles and MolarityMoles and Molarity

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

given massgiven mass

• MolarityMolarity– Is the number of moles of solute per liter of solutionIs the number of moles of solute per liter of solution– A 1M solution has 1 mole of solute in 1 L of water. (Remember: A 1M solution has 1 mole of solute in 1 L of water. (Remember:

1 mole of any substance is equal to its molecular weight in 1 mole of any substance is equal to its molecular weight in grams)grams)

2525

Acids and BasesAcids and Bases

• Dissociation of water moleculesDissociation of water molecules leads to acidic and basic conditions leads to acidic and basic conditions that affect living organismsthat affect living organisms

• Organisms must maintain Organisms must maintain homeostasis in the homeostasis in the pH pH of their of their internal and external environmentsinternal and external environments

2626

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

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

H

Hydroniumion (H3O+)

H

Hydroxideion (OH–)

H

H

H

H

H

H

+ –

+Figure of water dissociating

Effects of Changes in pHEffects of Changes in pH

2727

Acids and BasesAcids and Bases

• An An acidacid– Is any substance that Is any substance that increasesincreases the the hydrogen ion hydrogen ion

concentration of a solutionconcentration of a solution

• A A basebase– Is any substance that Is any substance that reducesreduces the the hydrogen ion hydrogen ion

concentration of a solutionconcentration of a solution

2828

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 The pH of a solution is determined by the relative relative concentration of hydrogen ionsconcentration of hydrogen ions

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

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

• AcidsAcids produce produce H+ ionH+ ion in solution in solution

• BasesBases produce produce OH- ions OH- ions in solutionin solution

2929

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 internal pH of most living cellsThe internal pH of most living cells– Must remain close to pH 7Must remain close to pH 7

• BuffersBuffers– Are substances that minimize changes Are substances that 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

3131

The Threat of Acid PrecipitationThe Threat of Acid Precipitation

• Acid precipitationAcid precipitation– Refers to rain, snow, or fog with a pH Refers to rain, snow, or fog with a pH

lower than pH 5.6lower than pH 5.6

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

3232

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

0

12

3

45

6

7

8

9

10

1112

13

14

Moreacidic

Acidrain

Normalrain

Morebasic

Figure 3.9

• Make sure you have read Chapter 3 in Make sure you have read Chapter 3 in CampbellCampbell

““Water and the Fitness of the Environment”Water and the Fitness of the Environment”

• You should also read Chapter 4 You should also read Chapter 4

““Carbon and the Molecular Diversity of Life”Carbon and the Molecular Diversity of Life”

We are starting this section – We are starting this section – NOWNOW!!

3333