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PowerPoint Lectures forBiology, Seventh Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero

Chapter 3

Water and the Fitness of

the Environment

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Concept 3.1: The polarity of water molecules results inhydrogen bonding

Polar

opposite ends of the molecule haveopposite charges

Polarity allows water molecules to form hydrogen

bonds with each other Oxygen is more electronegative

Animation: Water Structure

Hydrogenbonds

http://media/03_02WaterStructure_A.htmlhttp://media/03_02WaterStructure_A.html

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Concept 3.2: Four emergent properties of watercontribute to Earths fitness for life

Four of waters properties that facilitate anenvironment for life:

Cohesive behavior

Ability to moderate temperature

Expansion upon freezing

Versatility as a solvent

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Cohesion

Cohesionwhen water molecules bond to eachother by hydrogen bonds

helps the transport of water against gravity in

plantsAdhesion 2 different substances sticking together

Animation: Water Transport

http://media/03_03WaterTransport_A.htmlhttp://media/03_03WaterTransport_A.htmlhttp://media/03_03WaterTransport_A.html

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LE 3-3

Water-conducting cells

100 m

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Surface tension is a measure of how hard it is tobreak the surface of a liquid

Surface tension is related to cohesion

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Heat is absorbed when hydrogen bonds break

Heat is released when hydrogen bonds form

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Moderation of Temperature

High Heat Capacity Water can absorb or release a large amount of

heat with only a slight change in its owntemperature

Heat is absorbed to break a hydrogen bond

Heat is released when a hydrogen bond is

formed

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Heat and Temperature

Kinetic energy is the energy of motion Heat - totalamount of kinetic energy due to

molecular motion

Temperature - intensity of heat due to theaveragekinetic energy

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Waters High Specific Heat

The specific heat of a substance:

is the amount of heat that must be absorbed orlost for 1 gram of that substance to change itstemperature by 1C

Example: boiling water in an iron pot

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Insulation of Bodies of Water by Floating Ice

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The Solvent of Life

A solution is a liquid that is a homogeneousmixture of substances

solvent

solute

An aqueous solution is one in which water is the

solvent

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LE 3-6

In water, ionic molecules are pulled apart by

the H2O They dissolve

In water, polar molecules do not dissolve, but

H2O is still attracted to the molecule (colloid)

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Hydrophilic and Hydrophobic Substances

A hydrophilic substance is one that has anaffinity for water

A hydrophobic substance is one that does nothave an affinity for water

It is non-polar

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Molecular mass = sum of all masses of all atomsin a molecule (Measured in Daltons)

Numbers of molecules are usually measured inmoles, with one mole being 6.02 x 1023 molecules

-Avogadros Number

Molarity is the number of moles of solute per liter

of solution

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Concept 3.3: Dissociation of water molecules leads toacidic and basic conditions that affect living organisms

A hydrogen atom in a hydrogen bond between twowater molecules can shift from one to the other:

hydrogen atom is transferred as a proton, orhydrogen ion (H+)

The molecule with the extra proton is now ahydronium ion (H3O

+)

The molecule that lost the proton is now ahydroxide ion (OH-)

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Acids and Bases

acid increases the

H+ concentration

base reduces theH+ concentration

pH represents theH+ ions present

pH Scale01

2

3456789

1011121314 Oven cleaner

Household bleachHousehold ammoniaMilk of magnesia

Seawater

Pure waterHuman blood

UrineRainwaterBlack coffeeTomato juiceVinegar, beer, wine,colaDigestive (stomach)juice, lemon juice

Battery acid

Neutral[H+] = [OH]

IncreasinglyAcid

ic

[H+]>[OH]

IncreasinglyBasic

[H+]