ap bio ch 3

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Chapter 3

Water and the Fitness of

the Environment

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Importance of water

• Overview: The Molecule That

Overview: The Molecule That

Supports All of Life

• Water is the

Water is the

biological medium

here on Earth

• All living

All living

organisms require water

more than any other substance

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Water Facts

•

Three-quartersThree-quarters of the Earth’s of the Earth’s surface is submerged in water

surface is submerged in water

•

The abundance of water is the main The abundance of water is the main reason the

reason the Earth is habitable_{Earth is habitable}

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Water Facts

•

The The polarity of waterpolarity of water molecules molecules results in

results in hydrogen bondinghydrogen bonding

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Water’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 other

– Contributes to the _{Contributes to the}various properties_{various properties}

water exhibits

Hydrogen bonds

+

+ H

H

+

 –

–

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Properties of water

•

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

contribute 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.

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Cohesion

•

Water molecules exhibit cohesionWater molecules exhibit cohesion

•

CohesionCohesion

– Is the Is the bonding of a high percentage of bonding of a high percentage of the molecules to neighboring water

the molecules to neighboring water molecules

molecules

– Is due to Is due to hydrogen bondinghydrogen bonding

– Like molecules_{Like molecules} bonding to each other _{bonding to each other}

(water attracting other water molecules)

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Cohesion

•

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

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Surface Tension

•

Surface tensionSurface tension

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

the surface of a liquid of a liquid

– Is Is related to cohesionrelated to cohesion

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Moderation of Temperature

•

Water Water moderates air temperaturemoderates air temperature

•

By absorbing heat from airBy absorbing heat from air that is that is warmer and

warmer and releasing the stored heat _{releasing the stored heat}

to air that is cooler

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Heat 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 molecular motionIs a measure of the total amount of kinetic energy due to molecular motion

• TemperatureTemperature

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Water’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 1ºC

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Specific Heat

•

Water has a Water has a high specific heathigh specific heat which which allows it to

allows it to minimize temperature minimize temperature fluctuations

fluctuations to within limits that _{to within limits that}

permit life

– Heat is absorbedHeat is absorbed when hydrogen when hydrogen bonds break

bonds break

– Heat is released_{Heat is released} when hydrogen _{when hydrogen}

bonds form

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Evaporative 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 be Is the quantity of heat a liquid must absorb for 1 gram of it to be converted from a liquid to a gas

converted from a liquid to a gas

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Evaporative Cooling

•

Is due to water’s

high heat of

vaporization

•

Allows water to cool a surface

•

Sweating cools the body

as heat

energy from the body changes

sweat into a gas

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Insulation of Bodies of

Water by Floating Ice

•

Solid water, or

ice

–

Is

_Is

less dense

_{less dense}

than liquid water

_{than liquid water}

–

Floats

in liquid water

–

Insulates water & organisms

_{Insulates water & organisms}

below ice layer

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Insulation of Bodies of Water

by Floating Ice

•

The The hydrogen bondshydrogen bonds in ice in ice

– Are more “ordered” than in liquid water, Are more “ordered” than in liquid water, making ice less dense

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

Liquid water

Hydrogen bonds

constantly break and re-form

Ice

Hydrogen bonds are stable Hydrogen

bond

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Insulation of Bodies of Water

by Floating Ice

•

Since ice floats in water

–

Life can exist under the frozen

_{Life can exist under the frozen}

surfaces of lakes and polar seas

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The Solvent of Life

•

Water is a

versatile solvent due

to its polarity

•

It can form

aqueous solutions

•

Called the

universal solvent

because so many substances

dissolve in water

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•

The different regions of the polar water The different regions of the polar water molecule can interact with

molecule can interact with ionic _ionic

compounds called solutes and dissolve

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–_).

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•

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

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.

+

–

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Hydrophilic and Hydrophobic

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

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Solute Concentration in

Aqueous Solutions

•

Since Since most biochemical reactions occur in most biochemical reactions occur in water inside cells (aqueous environments)

water inside cells (aqueous environments)

– It is important to learn to calculate the It is important to learn to calculate the concentration of solutes

concentration of solutes in an aqueous in an aqueous solution

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Moles and Molarity

• A moleA mole

– Represents an exact number of molecules of a Represents an exact number of molecules of a substance in a given mass

substance in a given mass

• MolarityMolarity

– Is the number of moles of solute per liter of Is the number of moles of solute per liter of solution

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Acids and Bases

•

Dissociation of water molecules

leads to acidic and basic

conditions that affect living

organisms

•

Organisms must maintain

homeostasis

in the

_{in the}

pH

_pH

of their

_{of their}

internal and external environments

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•

Water can dissociate Into Water can dissociate Into hydronium hydronium ions (

ions (H+ or H_{H+ or H}₃₃O+)_O+) and _andhydroxide_hydroxide (OH-) _(OH-)

ions

•

Changes in the concentration of these Changes in the concentration of these ions Can have a great

ions Can have a great affect on pHaffect on pH in in living organisms

living organisms

H

Hydronium ion (H₃O+₎

H

Hydroxide ion (OH–₎

H H H H H H + – +

Figure on p. 53 of water dissociating

Effects of Changes in pH

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Acids and Bases

• An acidAn acid

– Is any substance that increases the Is any substance that increases the hydrogen ion hydrogen ion concentration

concentration of a solution of a solution

• A baseA base

– Is any substance that Is any substance that reduces the hydrogen ion reduces the hydrogen ion concentration

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The 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 values

•

Acids have a higher number of H+ ions Acids have a higher number of H+ ions

than a base

•

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

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The pH scale and pH values of

various aqueous solutions

In cr ea si ng ly A ci d ic [H + ] > [ O H – ] In cr ea si ng ly B a si c [H + ] < [ O H – ] 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 juice Vinegar, beer, wine, cola Tomato juice Black coffee Rainwater Urine Pure water Human blood Seawater

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Buffers

•

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 in minimize changes in the concentrations of hydrogen and