CAMPBELL
BIOLOGY
Outline
TENTH
EDITION
Reece • Urry • Cain • Wasserman • Minorsky • Jackson
I.
Water
A. Properties of water
3
II. Acids and Bases
Water
and Life
Dr Burns
NVC
© 2014 Pearson Education, Inc.
Water – The Life Giving Molecule

Why are we so interested in finding evidence
of water on Mars?

What would it mean if we did not find
evidence of water? Or if we find evidence?
Does it matter what form the water is?

Life exists here because water is abundant
Polar covalent bonds result in hydrogen
bonding
 In the water molecule, the electrons of the
polar covalent bonds spend more time
near the oxygen than the hydrogen
 The water molecule is thus a polar
molecule:
the overall charge is unevenly distributed
 Polarity allows water molecules to form
hydrogen bonds with each other
Water’s Abundance

71% of Earth’s surface is water



97.5% of the water is salt water
Freshwater only accounts for 2.5% of water
Only 0.53% is available to us to drink (rivers,
lakes, ground water)

66% of the human body is water by weight

70-95% of a cell’s weight is water
Figure 3.2
−
Hydrogen
bond
+
+
Polar covalent
bonds
−
−
+
+
−
1
Animation: Water Structure
Four properties of water important for life
 Four of water’s properties that facilitate an
environment for life are




Properties of Water
Cohesion vs Adhesion

1. Due to the hydrogen bonding, water has
cohesion (the water molecules cling together)
Cohesive behavior
Ability to moderate temperature
Expansion upon freezing
Versatility as a solvent
What is the difference between cohesion and
adhesion?
a) Important in blood flow through capillaries
b) Pulls water up plants from roots to the leaves
Cohesion of Water Molecules
Figure 3.3
H2O
 Collectively, hydrogen bonds hold water
molecules together, a phenomenon called
cohesion
 Cohesion helps the transport of water
against gravity in plants
 Adhesion is an attraction between
different substances, for example,
between water and plant cell walls
Adhesion
Two types
of waterconducting
cells
Direction
of water
movement
H2O
Cohesion
300 m
H2O
2
BioFlix: Water Transport in Plants
Surface Tension
Animation: Water Transport
Figure 3.4
 Surface tension is a measure of how hard
it is to break the surface of a liquid
 Water has an unusually high surface
tension due to hydrogen bonding between
the molecules at the air-water interface
and to the water below
Properties of Water
2. Due to hydrogen bonds, water has a high specific
heat and high heat of vaporization. This means
the temperature of water rises and falls slowly
Specific Heat
 What is the definition of Specific Heat?
a) preventing sudden changes in temperature, keeps
living organisms at a stable temperature
b) sweating cools organisms
3
Water’s High Specific Heat
 The specific heat of a substance is the
amount of heat that must be absorbed or
lost for 1 g of that substance to change its
temperature by 1°C
Moderation of Temperature by Water
 Due to the number of hydrogen bonds,
water can absorb or release a large
amount of heat with only a slight change in
its own temperature
 Water resists changing its temperature
because of its high specific heat
Evaporative Cooling
 Evaporation is transformation of a substance
from liquid to gas
 Heat of vaporization is the heat a liquid must
absorb for 1 g to be converted to gas
What type of bond between water molecules
creates surface tension that gives water cohesion?
1. Ionic
2. Covalent
3. Hydrogen
33%
33%
33%
 As a liquid evaporates, its remaining surface
cools, a process called evaporative cooling
 Evaporative cooling of water helps stabilize
temperatures in organisms and bodies of water
1
2
3
© 2011 Pearson Education, Inc.
Properties of Water
Figure 3.6
3. Due to the hydrogen bonding, ice has a lower
density than water (ice floats)
a) Lakes do not freeze allowing fish to survive the
winter
b) Polar ice caps are an important habitat
Hydrogen bond
Liquid water:
Hydrogen bonds
break and re-form
Ice:
Hydrogen bonds
are stable
4
4.
Properties of
Properties
ofWater:
WaterAn excellent solvent
4. Because water is polar it acts as a solvent for
polar and charged molecules, allows solutes to
remain in solution
a) Keeps molecules and ions in solution inside cells
and in blood.
Solvents
 A solution is a liquid that is a completely
homogeneous mixture of substances
 A solvent is the dissolving agent of a
solution
 The solute is the substance that is
dissolved
 An aqueous solution is one in which water
is the solvent
Water as a solvent
Figure 3.7

Like dissolves in like, so polar molecules
dissolve in water

Water is considered the best polar solvent
Hydrophilic and Hydrophobic Substances
−
Na+
+
+
−
−
Na+
+
Cl−
Cl–
−
+
+
−
−
−
+
−
−
+
−
 A hydrophilic substance is one that has an
affinity for water, polar molecules.
+
−
 A hydrophobic substance is one that does
not have an affinity for water, nonpolar
molecules.
5
Hydrophobic molecules are __________ by water
Acids and Bases

1. Attracted
2. Repelled
50%
50%
Acids – Substances that increases the solution’s
hydrogen ion concentration


Bases – Substances that decreases the
solution’s hydrogen ion concentration



 An acid is any substance that increases the
H+ concentration of a solution
 A base is any substance that reduces the H+
concentration of a solution
 Strong acids and bases dissociate
completely in water
 Weak acids and bases reversibly release
and accept back hydrogen ions, but can still
shift the balance of H+ and OH− away from
neutrality
Ph Scale

The strength of acids and bases is measured
using the pH scale.

pH = -log10[H+]

[H+] = conc in moles per liter
Ph Scale
It is inverse relationship:

Ph Scale

Scale from 0 – 14
Higher the pH the lower the concentration of H+


Logarithmic:

H+ + Cl- + Na+ + OH-  H2O + NaCl
2
Acids and Bases

NaOH  Na+ + OHH+ + OH-  H2O
In solution:

1
HCl  H+ + Cl-
Each point increase in pH represents a ten-fold
decrease in H+ concentration.


0 is the most acidic
14 is the most basic
7 is neutral (pure water)
6
Figure 3.10
Figure 3.10a
pH Scale
0
+
– H
H+ OH
+
OH– H H+
H+ H+
Acidic
solution
OH–
OH–
H+ H+ OH–
OH– OH–
+
H+ H+ H
Neutral
solution
OH–
OH–
OH– H+ OH–
–
OH– OH
OH–
H+
Basic
solution
Neutral
[H+] = [OH−]
Increasingly Basic
[H+] < [OH−]
H+
Increasingly Acidic
[H+] > [OH−]
1
H+
Battery acid
2 Gastric juice, lemon juice
3 Vinegar, wine,
cola
4 Tomato juice
Beer
5 Black coffee
Rainwater
6 Urine
Saliva
7 Pure water
Human blood, tears
8 Seawater
Inside of small intestine
9
OH−
OH−
OH−
H+
OH−
OH−
H+
OH−
OH−
Basic
solution
10
Milk of magnesia
11
OH−
H+
OH−
H+
OH−
H+
OH−
H+
OH−
H+
H+
H+
OH−
OH−
H+
H+
H+
H+
H+
Acidic
solution
Neutral
solution
Household ammonia
12
Household
13 bleach
Oven cleaner
14
Figure 3.UN04
The higher the pH a solution has, the higher the H+
concentration
0
Acidic
[H+] > [OH−]
Neutral
[H+] = [OH−]
Basic
[H+] < [OH−]
Acids donate H+ in
aqueous solutions.
1. True
2. False
50%
50%
7
Bases donate OH−
or accept H+ in
aqueous solutions.
14
1
2
Is a pH of 8 acidic or basic?
1. Acidic
2. Basic
50%
1
50%
 Changes in concentrations of H+ and OH−
can drastically affect the chemistry of a cell
2
7
Buffers
 The internal pH of most living cells must
remain close to pH 7
 Buffers are substances that minimize
changes in concentrations of H+ and OH− in
a solution
 Most buffer solutions contain a weak acid
and its corresponding base, which combine
reversibly with H+ ions
Fig. 2.16
Buffers
 Buffers resist changes in pH when an acid or
base is added.
 For example when CO2 enters the blood it
combines with H2O to form carbonic acid
(H2CO3). This weak acid dissociates to form
H+ and bicarbonate ion (HCO3-)
Page 30
Important Concepts

Reading for next lecture: Chapter 4

Know the vocabulary for this lecture/chapter
What are the properties of water and why are
these properties important to biology and life



Be able to describe acids, bases, and buffers.
Understand the pH scale
8