chapter 3 water and the fitness of the environment 1
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Chapter 3
Water and the Fitness of the Environment
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Why is water so important?
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Importance of water
• Cell chemistry occurs in the watery cytoplasm
• Water moderates temperatures
• Universal solvent
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How much of the earth is water?
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Water Facts• Three-quarters of
the Earth’s surface is water
• The abundance of water is the main reason the Earth is habitable
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What important fact about water have we already learned?
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Water Facts
• The water molecule is polar • The polarity results in hydrogen bonding
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How does hydrogen bonding relate to the properties of water?
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Hydrogenbonds
+
+
H
H+
+
–
–
–
–
Figure 3.2
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Properties of water
• Six emergent properties of water contribute to Earth’s fitness for life
1.Cohesion/Adhesion2.Surface tension3.Temperature Moderation4.High specific heat5.Evaporative cooling6.Universal solvent
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Emergent Properties
• Emergent properties – result from the arrangement and interaction of parts
within a system – may characterize nonbiological entities as well
• a functioning bicycle emerges only when all of the necessary parts connect in the correct way
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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The Power and Limitations of Reductionism
• Reductionism – the reduction of complex systems to
simpler components that are more manageable to study
• Ex. the molecular structure of DNA
• Understanding biology– balances reductionism with the study of
emergent properties• Ex. new understanding comes from studying
the interactions of DNA with other molecules
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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What do we mean by cohesion of water molecules?
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Cohesion
• Cohesion– the bonding of a high percentage of the
molecules to neighboring water molecules– Results from hydrogen bonding
• water attracting other water molecules
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How does the cohesion of water affect living things?
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Cohesion
– Helps pull water up through the microscopic vessels of plants (capillarity)
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Water conducting cells
100 µm
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What is surface tension?
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Surface Tension
– a measure of how hard it is to break the surface of a liquid
– related to cohesion
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Why do desert temperatures range from very hot during the day to very cold at night but areas near large bodies of water have a smaller temperature range?
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Moderation of Temperature
• Water absorbs heat from air that is warmer and releases the stored heat to air that is cooler–heats up slowly and cools down
slowly
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Heat and Temperature
• Heat–a measure of the total amount of
kinetic energy due to molecular motion
• Temperature–Measures the intensity of heat
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Water’s High Specific Heat
• specific heat –the amount of heat that must be
absorbed or lost for 1 gram of that substance to change its temperature by 1ºC
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Relate water’s molecular structure to its high specific heat.
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Specific Heat
• When heat is absorbed, hydrogen bonds break
• When heat is released, hydrogen bonds form–Water’s high specific heat allows it to
minimize temperature fluctuations within limits that permit life
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Why is evaporation a cooling process?
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Evaporative Cooling
• Evaporation– the transformation of a substance from a
liquid to a gas– Requires energy
• Heat of vaporization– the quantity of heat a liquid must absorb
for 1 gram of it to be converted from a liquid to a gas
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Evaporative Cooling
• due to water’s high heat of vaporization• 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–less dense than liquid water–Floats in liquid water–Insulates water & organisms below ice
layer
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Why is ice less dense than water?
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Floating Ice
• The hydrogen bonds in ice– Are more “ordered” than in liquid water, making
ice less dense (crystal lattice)
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Liquid water
Hydrogen bonds constantly break and re-form
IceHydrogen bonds are stable
Hydrogen bond
Figure 3.5
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Floating Ice
• Since ice floats in water–Life can exist under frozen lakes and seas
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Why do so many substances dissolve easily in water?
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The Solvent of Life
–Water is a solvent due to its polarity• Forms aqueous solutions• the universal solvent
–because so many substances dissolve in it
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• Different regions of the polar water molecule interact with ionic compounds called solutes and dissolve them
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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–
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• Water can also interact with polar molecules such as proteins
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This oxygen is attracted to a slight positive charge on the lysozyme molecule.
This hydrogen 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
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What kind of substances do not mix well with water?
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Hydrophilic and Hydrophobic Substances
• A hydrophobic substance– No affinity for water– Nonpolar– Lipids – oil, fat, wax
• A hydrophilic substance– Has an affinity for water– Polar or ionic– Carbohydrates, salts
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Solute Concentration in Aqueous Solutions
• Since most biochemical reactions occur in water inside cells–It is important to learn to calculate
the concentration of solutes in an aqueous solution
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Moles and Molarity
• A mole–Represents an exact number of
molecules of a substance in a given mass
• Molarity–Is the number of moles of solute per
liter of solution41
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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 pH of their internal and external environments
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Effects of Changes in pH
• Water can dissociate Into hydronium ions (H+ or H3O+) and hydroxide (OH-) ions
• Changes in the concentration of these ions Can have a great affect on pH in living organisms
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H
Hydroniumion (H3O+)
H
Hydroxideion (OH–)
H
H
H
H
H
H
+ –
+
Figure on p. 53 of water dissociating
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Acids and Bases
• An acid–any substance that increases the
hydrogen ion concentration of a solution
• A base–any substance that reduces the
hydrogen ion concentration of a solution (more OH- ions)
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The pH Scale• Scale goes from 0-14 with 7 neutral• The pH of a solution Is determined by the
relative concentration of hydrogen ions• Difference of 10X in hydrogen ion
concentration between any two pH values• Acids have a higher number of H+ ions than a
base• Acids produce H+ ion in solution• Bases produce OH- ions in solution
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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 juice
Vinegar, beer, wine,cola
Tomato juice
Black coffee Rainwater
Urine
Pure waterHuman blood
Seawater
Milk of magnesia
Household ammonia
Household bleach
Figure 3.8
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Buffers
• The internal pH of most living cells– Must remain close to pH 7
• Buffers– substances that minimize changes in the
concentrations of hydrogen and hydroxide ions in a solution
– Consist of an acid-base pair that reversibly combines with hydrogen ions
– Made by organisms
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The Threat of Acid Precipitation
• Acid precipitation–Refers to rain, snow, or fog with a pH
lower than pH 5.6–Caused by the mixing of different
pollutants with water in the air
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• Acid precipitation–Damages life in Earth’s ecosystems
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0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Moreacidic
Acidrain
Normalrain
Morebasic
Figure 3.9