Water and the Fitness of the Environment Part I. Polarity and Emergent Properties.

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

Part I. Polarity and Emergent Part I. Polarity and Emergent PropertiesProperties

You Should Know Chap. 3You Should Know Chap. 3

• The importance of hydrogen bonding The importance of hydrogen bonding to the properties of waterto the properties of water

• Four unique properties of water and Four unique properties of water and how each contributes to life on Earthhow each contributes to life on Earth

• How to interpret the pH scaleHow to interpret the pH scale

• The importance of buffers in The importance of buffers in biological systembiological system

Overview: The Molecule That Overview: The Molecule That Supports All of LifeSupports All of Life• Water is the biological medium on EarthWater is the biological medium on Earth

• All living organisms require water more All living organisms require water more than any other substancethan any other substance

• Most cells are surrounded by water, and Most cells are surrounded by water, and cells themselves are about 70–95% cells themselves are about 70–95% waterwater

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

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Concept 3.1: The polarity of water molecules results in hydrogen bonding

• The water molecule is a The water molecule is a polar moleculepolar molecule: : The opposite ends have opposite chargesThe opposite ends have opposite charges

• Polarity allows water molecules to form Polarity allows water molecules to form hydrogen bonds with each otherhydrogen bonds with each other

• Each water molecule can form a maximum Each water molecule can form a maximum of four hydrogen bonds at a timeof four hydrogen bonds at a time

Animation: Water StructureAnimation: Water Structure


Fig. 3-2Fig. 3-2

Hydrogenbond

–H

+

H

O

——

——

+ +

+

–

–

–

Concept 3.2: Four emergent properties of water Concept 3.2: Four emergent properties of water contribute to Earth’s fitness for lifecontribute to Earth’s fitness for life

• Four of water’s properties that Four of water’s properties that facilitate an environment for life are:facilitate an environment for life are:

– Cohesive behaviorCohesive behavior– Ability to moderate temperatureAbility to moderate temperature– Expansion upon freezingExpansion upon freezing– Versatility as a solventVersatility as a solvent


3.2-Cohesion3.2-Cohesion

• Collectively, hydrogen bonds hold Collectively, hydrogen bonds hold water molecules together, a water molecules together, a phenomenon called phenomenon called cohesioncohesion

• Cohesion helps the transport of water Cohesion helps the transport of water against gravity in plantsagainst gravity in plants

• Adhesion Adhesion is the clinging of one is the clinging of one substance to another. Example, substance to another. Example, between water and plant cell wallsbetween water and plant cell walls

Animation: Water TransportAnimation: Water Transport


Cohesion/Adhesion in Cohesion/Adhesion in NatureNature

• Transpiration- water molecules move Transpiration- water molecules move up the very thin xylem tubes and up the very thin xylem tubes and their evaporation the stomates in the their evaporation the stomates in the plant. Water molecules cling to each plant. Water molecules cling to each other because of cohesion and to the other because of cohesion and to the walls of the xylem tubes by walls of the xylem tubes by adhesion.adhesion.

Fig. 3-3Fig. 3-3

Water-conductingcells

Adhesion

Cohesion

150 µm

Directionof watermovement

• Surface tension Surface tension is a measure of how is a measure of how hard it is to break the surface of a liquidhard it is to break the surface of a liquid

• Surface tension is related to cohesionSurface tension is related to cohesion


Fig. 3-4Fig. 3-4

3.2 Ability to Moderate 3.2 Ability to Moderate TemperatureTemperature

• Water absorbs heat from warmer air Water absorbs heat from warmer air and releases stored heat to cooler airand releases stored heat to cooler air

• Water can absorb or release a large Water can absorb or release a large amount of heat with only a slight amount of heat with only a slight change in its own temperaturechange in its own temperature

3.2 Ability to Moderate Temp.-Water’s High Specific Heat3.2 Ability to Moderate Temp.-Water’s High Specific Heat

• The The specific heat specific heat of a substance is the amount of of a substance is the amount of heat that must be absorbed or lost for 1 g of that heat that must be absorbed or lost for 1 g of that substance to change its temperature by 1ºCsubstance to change its temperature by 1ºC

• The specific heat of water is 1 cal/g/ºCThe specific heat of water is 1 cal/g/ºC• Water resists changing its temperature because of its Water resists changing its temperature because of its

high specific heat because:high specific heat because:– Heat is released when hydrogen bonds formHeat is released when hydrogen bonds form– Heat is absorbed when hydrogen bonds breakHeat is absorbed when hydrogen bonds break

• The high specific heat of water minimizes temperature The high specific heat of water minimizes temperature fluctuations to within limits that permit lifefluctuations to within limits that permit life


Fig. 3-5Fig. 3-5

San Diego 72°

40 miles

Pacific Ocean

70s (°F)

80s

90s

100s

Santa Barbara 73°

Los Angeles (Airport) 75°

Burbank90°

San Bernardino100°

Riverside 96°Santa Ana 84° Palm Springs

106°

Water and the Fitness of the Environment Part I. Polarity and Emergent Properties.

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