The Biology of The Biology of water…water…

Why are the unique properties of Why are the unique properties of water so essential to life?water so essential to life?

How does the molecular structure of How does the molecular structure of water drive its special properties?water drive its special properties?

What makes water What makes water special?special?

75% of the earth’s surface, 70% of all living things

Water is the only common substance Water is the only common substance that exists in the natural world in all that exists in the natural world in all three physical states of matter: solid three physical states of matter: solid ice, liquid water, and water vapour.ice, liquid water, and water vapour.

1. How does water rise from the roots of a redwood tree to the very top?

2. How do insects walk on water?

3. Why does ice float rather than sink?

4. Why do people become seriously ill, or die, if they go without liquid for a week or so?

5. How would life in a lake be affected if ice sank and lakes froze from the bottom up?

WaterWater

Important biological propertiesImportant biological properties

Cohesion, Adhesion, Surface TensionCohesion, Adhesion, Surface Tension High specific heatHigh specific heat Heat of vaporizationHeat of vaporization Solvent of lifeSolvent of life Insulation of bodies of water (floating ice) Insulation of bodies of water (floating ice)

in winterin winter

How does water do thisHow does water do this

Concept 1 Concept 1 Water is a polar Water is a polar

moleculemoleculeThe polarity of water molecules The polarity of water molecules

results in hydrogen bonding results in hydrogen bonding between moleculesbetween molecules

Molecular structure of water

Concept 1 The polarity of Concept 1 The polarity of water molecules results in water molecules results in

hydrogen bondinghydrogen bonding

The slightly negative The slightly negative regions of one molecule regions of one molecule are attracted to the are attracted to the slightly positive regions slightly positive regions of nearby molecules, of nearby molecules, forming a hydrogen forming a hydrogen bondbond

Each water molecule can Each water molecule can form hydrogen bonds form hydrogen bonds with up to four with up to four neighborsneighbors

CohesionCohesion, , Adhesion Adhesion and and Surface Surface tension tension are are phenomena phenomena which reflect which reflect the polarity of the polarity of the water the water molecules, and molecules, and hydrogen hydrogen bonds between bonds between water water molecules molecules adhesionadhesion

CohesionCohesion

The attraction of The attraction of likelike molecules to be molecules to be attracted to each other, as occurs with attracted to each other, as occurs with polar water moleculespolar water molecules

Such molecules form a highly dynamic Such molecules form a highly dynamic structure with many breaking and forming structure with many breaking and forming bondsbonds

Plays a key role in life processes, including Plays a key role in life processes, including transport of water and dissolved nutrients transport of water and dissolved nutrients against gravity in plantsagainst gravity in plants

Play from 35s

AdhesionAdhesion

Attraction process Attraction process between polar between polar molecules of molecules of different substances different substances (e.g. water/glass)(e.g. water/glass)

Again, due to the Again, due to the polarity of water and polarity of water and hydrogen bondinghydrogen bonding

Capillary Action isDue to Adhesion

How does the crown get How does the crown get water?water?

Surface tensionSurface tension

Surface tension is a property of the Surface tension is a property of the surface of a liquid that allows it to surface of a liquid that allows it to resist an external resist an external forceforce

It is a measure of the force necessary to It is a measure of the force necessary to stretch or break the surface of a liquidstretch or break the surface of a liquid

Related to cohesionRelated to cohesion Several effects of surface tension are Several effects of surface tension are

evident with waterevident with water Water has a relatively high surface Water has a relatively high surface

tensiontension

Let’s watch cohesion, Let’s watch cohesion, adhesion and surface adhesion and surface

tension in action!tension in action!

1. Filling up a penny!1. Filling up a penny!

• You have a penny, a beaker of water You have a penny, a beaker of water and a dropper pipette.and a dropper pipette.

• How many drops of water can fit on How many drops of water can fit on to the top of the penny?to the top of the penny?

• Now repeat the test using ethyl Now repeat the test using ethyl alcohol…alcohol…

Why does water bead?Why does water bead?

The water molecules The water molecules beneath the surface beneath the surface are pulled in all are pulled in all directions.directions.

The molecules at the The molecules at the surface are pulled surface are pulled together and in.together and in.

This creates a tighter This creates a tighter arrangement of arrangement of molecules at the molecules at the surface and the round surface and the round shape of a drop of shape of a drop of water.water.

Alcohol has one O–H bond which is polar but a large portion of the molecule is made up of C–H bonds which are non-polar.Alcohol molecules do not attract each other as strongly as water molecules and have a weaker surface tension.

2. The Magic pepper 2. The Magic pepper plate…plate…

The Magic pepper plateThe Magic pepper plate

The charged end of a detergent molecule The charged end of a detergent molecule attracts water molecules at the surface attracts water molecules at the surface in an outward direction. This disrupts in an outward direction. This disrupts the way the molecules normally attract the way the molecules normally attract at the surface and weakens the surface at the surface and weakens the surface tension, causing the drop to collapse.tension, causing the drop to collapse.

Why can these animals walk on water?

Water moderates Water moderates temperatures on Earth temperatures on Earth because it has a high because it has a high

heat capacityheat capacity

Water has a high Water has a high heat capacity heat capacity since its polar since its polar molecules are molecules are connected by connected by

hydrogen bondshydrogen bonds

Let’s have a Let’s have a demonstration!demonstration!

• The magic balloonThe magic balloon

Heat and TemperatureHeat and Temperature

All atoms and molecules have All atoms and molecules have kinetic kinetic energyenergy energy of motionenergy of motion

What is heat?What is heat? HeatHeat is a measure of the is a measure of the totaltotal quantity of quantity of

kinetic energy due to molecular motion in kinetic energy due to molecular motion in a body of matter.a body of matter.

TemperatureTemperature measures the intensity of measures the intensity of heat due to the heat due to the averageaverage kinetic energy of kinetic energy of molecules.molecules.

How does the polarity of How does the polarity of water help in temperature water help in temperature

moderation?moderation? In order for water to change from a liquid In order for water to change from a liquid

to a gas, it has to absorb a lot of energy to a gas, it has to absorb a lot of energy to first break the hydrogen bonds and to first break the hydrogen bonds and allow its molecules to speed up.allow its molecules to speed up.

So water absorbs a lot of energy before So water absorbs a lot of energy before increasing temperatureincreasing temperature

Large bodies of water can absorb a lot of Large bodies of water can absorb a lot of heat energy without chancing heat energy without chancing temperaturetemperature

Specific HeatSpecific Heat The amount of heat that must be The amount of heat that must be

absorbed or lost for 1 g of that absorbed or lost for 1 g of that substance to change its substance to change its temperature by 1temperature by 1°C °C

Water has a specific heat of Water has a specific heat of 1 1 cal/g/cal/g/ooC.C.

Important because water does not Important because water does not change temperature quickly & change temperature quickly & large bodies of water can store large bodies of water can store much heat to warm the air.much heat to warm the air.

How do we measure How do we measure temperature?temperature?

In most biological settings, temperature In most biological settings, temperature is measured on the is measured on the Celsius scaleCelsius scale ( (ooC).C). At sea level, water freezes at O At sea level, water freezes at O ooC and C and

boils at 100boils at 100ooC.C. Human body temperature averages 37 Human body temperature averages 37 ooC.C.

The Blog provides details of other The Blog provides details of other commonly used temperature scales, commonly used temperature scales, namely the Kelvin Scale and the namely the Kelvin Scale and the Farhenheit ScaleFarhenheit Scale

How does water’s high How does water’s high specific heat impact living specific heat impact living

things?things?Since the Since the

temperature of temperature of water rises and water rises and falls slowly, it is falls slowly, it is easier for easier for organisms to organisms to regulate and regulate and maintain a stable maintain a stable internal internal temperaturetemperature

How does water’s high How does water’s high specific heat impact specific heat impact

living things?living things?Large bodies of Large bodies of

water absorb water absorb heat during the heat during the day, release day, release heat at nightheat at night

Coastal Coastal temperatures temperatures remain relatively remain relatively constantconstant

Oceans/ lakes and Oceans/ lakes and atmospheric atmospheric

temperature regulationtemperature regulation Water stabilizes air temperatures by Water stabilizes air temperatures by

absorbing heat from warmer air and absorbing heat from warmer air and releasing heat to cooler air.releasing heat to cooler air.

Water can absorb or release Water can absorb or release relatively large amounts of heat with relatively large amounts of heat with only a slight change in its own only a slight change in its own temperaturetemperature

A lot of energy is A lot of energy is required to required to

convert water convert water into water into water

vapourvapour

Water has a Water has a high heat of high heat of vaporizationvaporization

Latent HeatLatent Heat

Latent Heat is the heat given up or absorbed by a substance as it changes state. It is called latent because it is not associated with a change in temperature

Vaporization/evaporationVaporization/evaporation

The transformation of a The transformation of a molecule from a liquid to a molecule from a liquid to a gas, occurs when the gas, occurs when the molecule moves fast molecule moves fast enough to overcome the enough to overcome the attraction of other attraction of other moleculesmolecules

Even in a low temperature Even in a low temperature liquid (low average kinetic liquid (low average kinetic energy), some molecules energy), some molecules are moving fast enough to are moving fast enough to evaporate.evaporate.

Heating a liquid Heating a liquid increases the increases the average kinetic average kinetic energy and increases energy and increases the rate of the rate of evaporation.evaporation.

Heat of Heat of vaporization is the vaporization is the quantity of heat quantity of heat that a liquid must that a liquid must absorb for 1 g of it absorb for 1 g of it to be converted to be converted from liquid to gas.from liquid to gas.

Water has a high heat of Water has a high heat of vaporizationvaporization

Water has a relatively high heat of Water has a relatively high heat of vaporization, requiring about 580 cal of heat vaporization, requiring about 580 cal of heat to evaporate 1 g of water at room to evaporate 1 g of water at room temperature.temperature.

This is double the heat required to vaporize This is double the heat required to vaporize the same quantity of alcohol or ammonia.the same quantity of alcohol or ammonia.

This is because hydrogen bonds must be This is because hydrogen bonds must be broken before a water molecule can broken before a water molecule can evaporate from the liquid.evaporate from the liquid.

up to 42s then 1.08 to end

Alcohol has one O–H Alcohol has one O–H bond which is polar bond which is polar but a large portion of but a large portion of the molecule is made the molecule is made up of C–H bonds up of C–H bonds which are nonpolar.which are nonpolar.

Alcohol molecules do Alcohol molecules do not attract each other not attract each other as strongly as water as strongly as water molecules and boil at molecules and boil at a lower temperature.a lower temperature.

Evaporative CoolingEvaporative Cooling

The high heat of The high heat of vapourisation provides vapourisation provides animals with an efficent animals with an efficent cooling mechanismcooling mechanism

• As we sweat, body heat As we sweat, body heat vapourises water and cools vapourises water and cools the body surface.the body surface.

• Evaporation of water from Evaporation of water from the leaves of plants cools the leaves of plants cools their surfacestheir surfaces

Evaporative cooling and Evaporative cooling and atmospheric temperature atmospheric temperature

regulationregulation

Evaporative cooling Evaporative cooling moderates moderates temperature in lakes temperature in lakes and ponds and and ponds and prevents terrestrial prevents terrestrial organisms from organisms from overheating.overheating.

Ice is less dense Ice is less dense than waterthan water

Ice Floats…Ice Floats…

Water is less dense as a solid than a Water is less dense as a solid than a liquidliquid

Usually substances shrink as they Usually substances shrink as they coolcool

Hydrogen bonding in ice causes Hydrogen bonding in ice causes water molecules to form a lattice, water molecules to form a lattice,

making it less dense than making it less dense than WaterWaterCanada Nature animation

How do living things How do living things benefit from water benefit from water

expanding as it freezes?expanding as it freezes?• If ice sank, eventually all ponds, If ice sank, eventually all ponds,

lakes, and even the ocean would lakes, and even the ocean would freeze solid.freeze solid.

• During the summer, only the During the summer, only the upper few centimeters of the upper few centimeters of the ocean would thaw.ocean would thaw.

• Instead, the surface layer of ice Instead, the surface layer of ice insulates liquid water below, insulates liquid water below, preventing it from freezing and preventing it from freezing and allowing life to exist under the allowing life to exist under the frozen surface.frozen surface.

Water is the Water is the solvent of lifesolvent of life

• MixturesMixtures• SolutionsSolutions• SuspensionsSuspensions

MixtureMixture

‘‘A material composed of two or A material composed of two or more elements or compounds more elements or compounds that are physically mixed but that are physically mixed but

not chemically combined’not chemically combined’

SolutionSolution

A liquid that is a completely homogeneous A liquid that is a completely homogeneous mixture of two or more substances mixture of two or more substances

The dissolving agent is the solvent, The dissolving agent is the solvent, and the substance that is dissolved is and the substance that is dissolved is the solute.the solute.

In an aqueous solution, water is the In an aqueous solution, water is the solvent.solvent.

Water is not a universal solvent, but it is Water is not a universal solvent, but it is very versatile because of the polarity of very versatile because of the polarity of water molecules.water molecules.

Solution

SuspensionSuspension

‘‘Materials do not dissolve, but Materials do not dissolve, but separate into pieces so small that separate into pieces so small that they do not settle out,, rather are they do not settle out,, rather are

kept suspended by the movement of kept suspended by the movement of water molecules around them’water molecules around them’

Let’s take a look at the Let’s take a look at the behaviour of solutions behaviour of solutions

and suspensions!and suspensions!

Water can Water can dissolve other dissolve other polar polar compounds, compounds, ionic compounds ionic compounds and charged and charged compoundscompounds

Water is an excellent Water is an excellent solvent for ionic solvent for ionic

compoundscompounds• http://www.middleschoolchemistry.co

m/multimedia/chapter5/lesson3

Example: Sucrose Example: Sucrose dissolves easily in waterdissolves easily in water

• The ball-and-stick and first The ball-and-stick and first space-filling model show that space-filling model show that sucrose is a large molecule sucrose is a large molecule made up of carbon, oxygen, and made up of carbon, oxygen, and hydrogen.hydrogen.

• Sucrose has many O–H bonds Sucrose has many O–H bonds which are polar.These polar which are polar.These polar areas are shown with a + near areas are shown with a + near the hydrogen atom and a − the hydrogen atom and a − near the oxygen atom.near the oxygen atom.

• The second space-filling model The second space-filling model shows two sucrose molecules shows two sucrose molecules held together by their opposite held together by their opposite polar areas.polar areas.

• These molecules will separate These molecules will separate from each other when sucrose from each other when sucrose dissolves.dissolves.

Example: Sucrose Example: Sucrose dissolves easily in waterdissolves easily in water

• Sucrose animation

What types of substances What types of substances dissolve in water? What dissolve in water? What

substances don’t?substances don’t?

Even large Even large molecules, molecules, like proteins, can like proteins, can dissolve in water if dissolve in water if they have ionic or they have ionic or polar regionspolar regions

DefinitionsDefinitions

HydrophilicHydrophilic

Any substance that has Any substance that has an affinity for water: an affinity for water: ‘water loving’‘water loving’

• Contain many ionic or Contain many ionic or polar bondspolar bonds

• includes substances includes substances that do not dissolve that do not dissolve because their because their molecules are too molecules are too largelarge

HydrophobicHydrophobic

Substances that have Substances that have no affinity for water: no affinity for water: water fearingwater fearing

Contain many non-Contain many non-ionic and nonpolar ionic and nonpolar covalent bondscovalent bonds

Hydrophobic Hydrophobic molecules are major molecules are major ingredients of cell ingredients of cell membranes.membranes.

Acids, bases and pHAcids, bases and pH

Why do we care about Why do we care about pH?pH?

Organisms are sensitive to changes Organisms are sensitive to changes in pHin pH

Acid rainAcid rain Rain is typically acidic because it Rain is typically acidic because it

combines with COcombines with CO22 Normal rain pH 5.6Normal rain pH 5.6 Acid rain pH <5.6Acid rain pH <5.6

Result of pollutionResult of pollution Burning of fossil fuelsBurning of fossil fuels

Dissociation Dissociation of of water molecules leads water molecules leads

to acidic and basic to acidic and basic conditions that affect conditions that affect

living organismsliving organisms

Sometimes, an HSometimes, an H22O O molecule loses a Hmolecule loses a H++ ion that ion that

is in turn accepted by is in turn accepted by another Hanother H22OO

LecturePLUS Timberlake64

Ionization of WaterIonization of Water

Occasionally, in water, a HOccasionally, in water, a H++ is transferred is transferred between Hbetween H22O moleculesO molecules

. . . . . . . .. . . . . . . .HH::OO:: + + ::OO::H H H H::OO::H H ++ + + : :OO::HH--

. .. . . . . . . . . . . . . . HH HH H H

water moleculeswater molecules hydronium hydronium hydroxide hydroxide ion (+) ion (+) ion ion

(-)(-)

H+ leaves its electron behind and is H+ leaves its electron behind and is transferred as a single proton - a transferred as a single proton - a hydrogen ionhydrogen ion (H+) (H+)

The water molecule that lost a The water molecule that lost a proton is now a proton is now a hydroxidehydroxide ionion (OH-)(OH-)

The water molecule with the extra The water molecule with the extra proton is a proton is a hydroniumhydronium ion (H3O+) ion (H3O+)

HH22O <=> HO <=> H++ + OH + OH--

This reaction is reversible.This reaction is reversible. At equilibrium the concentration of water At equilibrium the concentration of water

molecules greatly exceeds that of Hmolecules greatly exceeds that of H++ and OH and OH--

At equilibrium the concentration of HAt equilibrium the concentration of H++ or OH or OH-- is 10 is 10--

77MM (25°C) (25°C) Adding solutes (acids or bases) changes the Adding solutes (acids or bases) changes the

concentration of Hconcentration of H++ and OH and OH--

Solutions with more OHSolutions with more OH-- than H than H++ are basic solutions. are basic solutions.

Solutions with more HSolutions with more H++ than OH than OH-- are acidic solutions. are acidic solutions.

Solutions in which concentrations of OHSolutions in which concentrations of OH-- and H and H++ are are equal are neutral solutions.equal are neutral solutions.

LecturePLUS Timberlake67

Pure Water is NeutralPure Water is Neutral

Pure water contains small, but equal Pure water contains small, but equal amounts of ions: Hamounts of ions: H33OO++ and OH and OH--

HH22O + HO + H22O O HH33OO++ + OH + OH--

hydronium hydroxide hydronium hydroxide

ion ion ion ion

1 x 101 x 10-7 -7 MM 1 x 101 x 10-7 -7

MM

H3O+ OH-

Acids & Bases

Acids are formed by hydrogen cations

Bases are formed by hydroxide anions

LecturePLUS Timberlake69

AcidsAcids

Increase HIncrease H++

HCl HCl (g)(g) + H + H22O O (l)(l) HH33OO++ (aq)(aq)

+ Cl+ Cl-- (aq)(aq)

More [HMore [H33OO++] than water > 1 x 10] than water > 1 x 10-7-7MM

As HAs H33OO++ increases, OH increases, OH-- decreases decreases

[H[H33OO++] > ] > [OH[OH--]]H3O+

OH-

Acids

Donate protons (Hydrogen Ions) to water to Donate protons (Hydrogen Ions) to water to form hydronium ionsform hydronium ions

pH 0-6.99 pH 0-6.99

Taste SourTaste Sour

Turn litmus paper red Turn litmus paper red

Strong acids completely dissociate to form ions completely dissociate to form ions

LecturePLUS Timberlake71

BasesBases

Increase the hydroxide ions (OHIncrease the hydroxide ions (OH--) )

HH22OO

NaOH (s) NaOH (s) Na Na++(aq) + OH(aq) + OH- - (aq)(aq)

More [OHMore [OH--] than water, ] than water, [OH[OH--] > 1 x ] > 1 x

1010-7-7MM

When OHWhen OH-- increases, H increases, H33OO++ decreases decreases

[OH[OH]] > > [H[H33OO++]]H3O+OH-

Bases Donate hydroxideDonate hydroxide pH 7.01-14pH 7.01-14 Accept protonsAccept protons Taste bitter Taste bitter

Feel slimyFeel slimy Turn litmus paper blueTurn litmus paper blue Strong bases completely dissociate to form ionsStrong bases completely dissociate to form ions

BasesBases

Base Base increases [OH- ] increases [OH- ] Some bases reduce the H+ concentration Some bases reduce the H+ concentration

directly by accepting hydrogen ionsdirectly by accepting hydrogen ions

For example, NHFor example, NH33 + H + H++ <=> NH <=> NH44++

Other bases reduce HOther bases reduce H++ indirectly by indirectly by dissociating to OHdissociating to OH--, which then combines , which then combines with H+ to form water.with H+ to form water.

For example, NaOH -> NaFor example, NaOH -> Na++ + OH + OH--

OHOH-- + H + H++ -> H -> H22OO

In a neutral solution In a neutral solution [H[H++] = 10] = 10-7-7 MM, and , and the pH = 7.the pH = 7.

Values for pH Values for pH declinedecline as [H as [H++] ] increaseincrease..

Most biological Most biological fluids??? fluids???

Each pH unit Each pH unit represents a represents a tenfoldtenfold difference in Hdifference in H++ and and OHOH-- concentrations. concentrations.

A small change in pH A small change in pH actually indicates a actually indicates a substantial change in substantial change in HH++ and OH and OH-- concentrationsconcentrations

Fig. 3.9

pHpH

pH DemonstrationpH Demonstration

Reading Quiz tomorrow!Reading Quiz tomorrow!

• On page 39 – 43On page 39 – 43• You can use any notes you have You can use any notes you have

made today or this evening…made today or this evening…• Quiz mark will count towards your Quiz mark will count towards your

interim grade.interim grade.