Chapter 2

Report
Chapter 2
The Chemical Basis of Life
PowerPoint Lectures for
Biology: Concepts and Connections, Fifth Edition
– Campbell, Reece, Taylor, and Simon
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Nature’s Chemical Language
• The rattlebox moth
–
Produces chemicals important for mating
and defense
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• The compound produced during mating
–
Allows the moths to communicate using
chemicals
• Thomas Eisner of Cornell University
–
Has studied this process in rattlebox moths
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• Chemicals play many more roles in life than
signaling
– Making up our bodies, those of other
organisms, and the physical environment
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ELEMENTS, ATOMS, AND MOLECULES
2.1 Living organisms are composed of about 25
chemical elements
• About 25 different chemical elements
– Are essential to life
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• Carbon, hydrogen, oxygen, and nitrogen
–
Make up the bulk of living matter
Table 2.1
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• Trace elements
– Are essential to life, but occur in minute
amounts
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CONNECTION
2.2: Trace elements are common additives to food
and water
• Dietary deficiencies in trace elements
–
Can cause various physiological conditions
Figure 2.2A
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• Trace elements are essential to human health
– And may be added to food or water
Figure 2.2B
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Fundamental Building Blocks
Matter - all materials that occupy space &
have mass
Matter is composed of atoms
Atom – simplest form of matter not divisible
into simpler substances
• composed of protons, neutrons, &
electrons
Element – atoms that differ in numbers of
protons, neutron & electrons
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Models of atoms
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2.3 Elements can combine to form compounds
• Chemical elements
–
Combine in fixed ratios to form compounds
Chlorine
Sodium
Figure 2.3
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Sodium Chloride
2.4 Atoms consist of protons, neutrons, and
electrons
• The smallest particle of matter that still retains
the properties of an element is an atom
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Subatomic Particles
• An atom is made up of protons and neutrons
–
Located in a central nucleus
• The nucleus is surrounded by electrons
–
Arranged in electron shells
– –
2e–
+
+
+
+
Electron
cloud
Nucleus
2 + Protons
2
Figure 2.4A
Neutrons
Mass
number = 4
2 – Electrons
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Differences in Elements
• Atoms of each element
–
Are distinguished by a specific number of
protons
Electron
cloud
6e–
++
Nucleus
6 + Protons
6
Figure 2.4B
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Neutrons
6 – Electrons
Mass
number = 12
Atomic number – number of protons
Mass number – number of protons & neutrons
Isotopes – variant forms of an element that differ
in mass number
Atomic weight – average of the mass numbers
of all of the element’s isotopic forms
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Isotopes
• The number of neutrons in an atom may vary
–
Variant forms of an element are called
isotopes
–
Some isotopes are radioactive
Table 2.4
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CONNECTION
2.5 Radioactive isotopes can help or harm us
• Radioactive isotopes are useful as tracers
– For monitoring the fate of atoms in living
organisms
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Basic Research
• Biologists often use radioactive tracers
– To follow molecules as they undergo
chemical changes in an organism
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Medical Diagnosis
• Radioactive tracers are often used for diagnosis
–
In combination with sophisticated imaging
instruments
Figure 2.5A
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Figure 2.5B
Dangers
• Radioactive isotopes have many beneficial uses
–
But uncontrolled exposure to them can harm
living organisms
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2.6 Electron arrangement determines the chemical
properties of an atom
• Electrons in an atom
–
Are arranged in shells, which may contain
different numbers of electrons
Outermost electron shell (can hold 8 electrons)
First electron shell (can hold 2 electrons)
Electron
Figure 2.6
Hydrogen (H)
Atomic number = 1
Carbon (C)
Atomic number = 6
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Nitrogen (N)
Atomic number = 7
Oxygen (O)
Atomic number = 8
• Atoms whose shells are not full
– Tend to interact with other atoms and
gain, lose, or share electrons
• These interactions
– Form chemical bonds
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Molecules & Bonds
Molecule – distinct chemical substance that results from
the combination of two or more atoms
Elements can combine to form compounds.
•
A.
Compounds contain two or more
atoms in a fixed ratio.
•
B.
Different combinations of atoms
determine the unique properties of each
compound.
Chemical bonds – when 2 or more atoms share, donate
or accept electrons.
3 types: covalent, ionic, & hydrogen
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3 Types of Chemical Bonds
Covalent bonds – electrons are shared
among atoms
•
polar covalent bonds– unequal sharing
•
nonpolar covalent bonds– equal sharing
Ionic bonds – electrons are transferred to
one atom forming positively charged
cations & negatively charged anions
Hydrogen bonds – weak bonds between
hydrogen & other atoms
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2.7 Ionic bonds are attractions between ions of
opposite charge
• When atoms gain or lose electrons
–
Charged atoms called ions are created
–
–
+
Transfer of
electron
Na
Cl
Na
Sodium atom
Cl
Chlorine atom
Figure 2.7A
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–
Na
Cl
Na+
Sodium ion
Cl–
Chloride ion
Sodium chloride (NaCl)
• An electrical attraction between ions with
opposite charges
– Results in an ionic bond
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Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• Sodium and chloride ions
–
Bond to form sodium chloride, common
table salt
Na+
Cl–
Figure 2.7B
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2.8 Covalent bonds join atoms into molecules
through electron sharing
• In covalent bonds
–
Two atoms share one or more pairs of outer
shell electrons, forming molecules
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• Molecules can be represented in many ways
Table 2.8
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Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
2.9 Unequal electron sharing creates polar
molecules
• A molecule is nonpolar
– When its covalently bonded atoms share
electrons equally
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• In a polar covalent bond
– Electrons are shared unequally between
atoms, creating a polar molecule
(–)
(–)
O
H
Figure 2.9
(+)
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H
(+)
Solution – a mixture of one or
more substances called solutes,
dispersed in a dissolving
medium called a solvent
Solutes – Na+ & ClSolvent – H2O
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Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
2.10 Hydrogen bonds are weak bonds important
in the chemistry of life
• The charged regions on water molecules
– Are attracted to the oppositely charged
regions on nearby molecules
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• This attraction forms weak bonds
– Called hydrogen bonds
(–)
Hydrogen bond
(+)
H
(+)
O
(–)
H
(–)
(+)
(–)
(+)
Figure 2.10
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WATER’S LIFE-SUPPORTING PROPERTIES
2.11 Hydrogen bonds make liquid water cohesive
• Due to hydrogen bonding
– Water molecules can move from a plant’s
roots to its leaves
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Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• Insects can walk on water due to surface
tension
– Created by cohesive water molecules
Figure 2.11
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2.12 Water’s hydrogen bonds moderate
temperature
• Water’s ability to store heat
– Moderates body temperature and climate
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• It takes a lot of energy to disrupt hydrogen
bonds
– So water is able to absorb a great deal of
heat energy without a large increase in
temperature
• As water cools
– A slight drop in temperature releases a
large amount of heat
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• A water molecule takes energy with it when it
evaporates
–
Leading to evaporative cooling
Figure 2.12
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2.13 Ice is less dense than liquid water
• Hydrogen bonds hold molecules in ice
–
Farther apart than in liquid water
Figure 2.13
Hydrogen bond
Ice
Hydrogen bonds are stable
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Liquid water
Hydrogen bonds
constantly break and re-form
• Ice is therefore less dense than liquid water
– Which causes it to float
• Floating ice
– Protects lakes and oceans from freezing
solid
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2.14 Water is the solvent of life
• Polar or charged solutes
–
Dissolve when water molecules surround
them, forming aqueous solutions
Na+
–
+
Na+
Cl–
–
+
Cl–
+
–
–
+
+
–
+
–
+
–
–
–
Ion in
solution
Figure 2.14
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Salt
crystal
–
2.15 The chemistry of life is sensitive to acidic
and basic conditions
• A compound that releases H+ ions in solution is
an acid
– And one that accepts H+ ions in solution
is a base
• Acidity is measured on the pH scale
– From 0 (most acidic) to 14 (most basic)
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• The pH scale
H+ H+
Acidic solution
OH–
OH–
OH–
H+ H+ –
OH– OH
H+ H+ H+
Neutral solution
OH–
OH–
OH– H+ OH–
OH– OH– –
OH
H+
Figure 2.15
Basic solution
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NEUTRAL
[H+]=[OH–]
Increasingly BASIC
(Lower concentration of H+)
+
H+ H
H+ OH– H+
OH– H+ H+
Increasingly ACIDIC
(Higher concentration of H+)
pH scale
0
1
2
Lemon juice, gastric juice
3
Grapefruit juice, soft drink
4
Tomato juice
5
6
Human urine
7
Pure water
Human blood
8
Seawater
9
10
Milk of magnesia
11
Household ammonia
12
Household bleach
13
Oven cleaner
14
• The pH of most cells
– Is kept close to 7 (neutral) by buffers
• Buffers are substances that resist pH change
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CONNECTION
2.16: Acid precipitation threatens the
environment
• Some ecosystems are threatened by acid
precipitation
• Acid precipitation is formed when air pollutants
from burning fossil fuels
– Combine with water vapor in the air to
form sulfuric and nitric acids
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• These acids
– Can kill trees and damage buildings
Figure 2.16A
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Figure 2.16B
CHEMICAL REACTIONS
2.17 Chemical reactions change the composition of
matter
• In a chemical reaction
–
Figure 2.17A
Reactants interact, atoms rearrange, and
products result
2 H2
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O2
2 H2O
• Living cells carry out thousands of chemical
reactions
–
That rearrange matter in significant ways
CH3
CH3
CH3
H2C
C
CH2
H2C
CH
C
CH
CH3
CH
C
CH
CH
C
C
CH
CH CH
C
CH3 CH3
CH
CH
C
CH3
CH
CH
CH
C
CH3
CH
C
CH3
CH2
H2C
CH2
C
CH2
CH3
Beta-carotene
Figure 2.17B
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CH3
CH3
O2
4H
2 CH2
H2C
CH
C
C
CH
CH3
H
C
C
CH
C
CH
CH
CH
C
CH3 CH3
Vitamin A
(2 molecules)
H
OH
Chapter 2
The Chemical Basis of Life
PowerPoint Lectures for
Biology: Concepts and Connections, Fifth Edition
– Campbell, Reece, Taylor, and Simon
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
1. Which four chemical elements are most
abundant in living matter?
2. Why are sodium chloride and vitamin A both
classified as compounds?
3. Why are radioactive isotopes useful as
tracers in research and medical testing?
4. Sodium has an atomic number of 11. How
many electron shells does it have and how
many electrons are in its outer shell?
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
1. What holds together the atoms in table salt?
2. What is wrong with the chemical structure HC=C-H?
3. What allows neighboring water molecules to
bond to each? What is the bond and how
does it work?
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1. In plants, water in thin tubes within the trunk
is pulled upward by evaporation from leaves.
What keeps the water molecules at the
bottom of the tree moving?
2. Explain the popular adage “It’s not the heat,
it’s the humidity.”
3. Explain how freezing of water can crack
boulders.
4. What is the relationship between fossil fuel
consumption and acid rain?
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Concept Check
In order to understand the chemical basis of inheritance,
one must understand the molecular structure of DNA.
This is an example of the application of __________ to the
study of biology?
•
emergent properties
•
the cell theory
•
reductionism
•
philosophy
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Answer
In order to understand the chemical basis of inheritance,
one must understand the molecular structure of DNA.
This is an example of the application of __________ to the
study of biology?
•
reductionism
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Concept Check
The reactive properties or chemical behavior of an atom
mostly depend on the number of
•
the electrons in each electron shell of the atom.
•
the neutrons found in the nucleus.
•
the filled electron shells.
•
the electrons in the outer electron shell of the atom.
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Answer
The reactive properties or chemical behavior of an atom
mostly depend on the number of
•
the electrons in the outer electron shell of the atom.
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Concept Check
Water molecules form hydrogen
bonds because
•
the water molecule is polar.
•
the oxygen molecule is
positively charged.
•
the water molecule forms a
tetrahedron.
•
the hydrogen atoms are
negatively charged.
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Answer
Water molecules form hydrogen
bonds because
•
the water molecule is polar.
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Interpreting Data
This is the general equation for photosynthesis—the process of
capturing sunlight energy and converting it to chemical energy.
Which of the following are the reactants of this reaction?
•
C6H12O6 and O2.
•
CO2 and H2O.
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Answer
This is the general equation for photosynthesis—the process of
capturing sunlight energy and converting it to chemical energy.
Which of the following are the reactants of this reaction?
•
CO2 and H2O.
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Interpreting Data
Earth’s oceans are immense. Small floating plants called
phytoplankton contribute to ocean productivity. As ocean
productivity (the rate of photosynthesis) goes up what would you
predict would happen to global carbon dioxide levels?
•
CO2 levels should also go up.
•
CO2 levels should go down
•
CO2 levels should remain constant.
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Answer
Earth’s oceans are immense. Small floating plants called
phytoplankton contribute to ocean productivity. As ocean
productivity (the rate of photosynthesis) goes up what would you
predict would happen to global carbon dioxide levels?
•
CO2 levels should go down
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Interpreting Data
Ironically, the world’s oceans
throughout the tropics are not very
productive. (these oceans do not
capture much sunlight through the
process of photosynthesis.) On
the other hand some of the most
productive ocean are the Arctic and
Antarctic. What might be limiting
production in the tropical oceans?
•
Low temperature.
•
Low sunlight.
•
Low nutrients.
•
High nutrients.
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Answer
Ironically, the world’s oceans
throughout the tropics are not very
productive. (these oceans do not
capture much sunlight through the
process of photosynthesis.) On
the other hand some of the most
productive ocean are the Arctic and
Antarctic. What might be limiting
production in the tropical oceans?
•
Low nutrients.
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Interpreting Data
– Iron is the fourth most common element (by
weight) in the Earth’s crust.
– Iron is an essential trace element for all living
organisms.
– Ocean waters, particularly the Southern Ocean
have very minute amounts of iron.
– The Iron hypothesis states that Iron availability
limits ocean productivity.
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Interpreting Data
These are the results
of a laboratory
experiment to test the
effect of trace nutrients
on the productivity of
Pacific Ocean water.
After 6 days which
nutrient had the
greatest effect on
productivity?
•
Iron.
•
Manganese.
•
Copper.
•
Zinc.
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Adapted from Coale, Kenneth H. 1991.
Effects of Iron, Manganese, Copper and Zinc
Enrichments on Productivity and Biomass in
the Subarctic Pacific. Limnology and
Oceanography. 36: 1851-1864
Answer
These are the results
of a laboratory
experiment to test the
effect of trace nutrients
on the productivity of
Pacific Ocean water.
After 6 days which
nutrient had the
greatest effect on
productivity?
•
Iron.
Adapted from Coale, Kenneth H. 1991.
Effects of Iron, Manganese, Copper and Zinc
Enrichments on Productivity and Biomass in
the Subarctic Pacific. Limnology and
Oceanography. 36: 1851-1864
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Interpreting Data
Some have suggested that fertilizing the oceans with iron
might be a possible solution to the increasing carbon dioxide
levels in the atmosphere. Iron’s function as a trace nutrient in
phytoplankton possibly affecting the atmosphere and possibly
global climate is a good example of?
•
The stability of atoms.
•
The unity of life on earth.
•
Emergent properties.
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Answer
Some have suggested that fertilizing the oceans with iron
might be a possible solution to the increasing carbon dioxide
levels in the atmosphere. Iron’s function as a trace nutrient in
phytoplankton possibly affecting the atmosphere and possibly
global climate is a good example of?
•
Emergent properties.
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

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