Unit 1: What is Biology?
Unit 2: Ecology
Unit 3: The Life of a Cell
Unit 4: Genetics
Unit 5: Change Through Time
Unit 6: Viruses, Bacteria, Protists, and Fungi
Unit 7: Plants
Unit 8: Invertebrates
Unit 9: Vertebrates
Unit 10: The Human Body
Unit 1: What is Biology?
Chapter 1: Biology: The Study of Life
Unit 2: Ecology
Chapter 2: Principles of Ecology
Chapter 3: Communities and Biomes
Chapter 4: Population Biology
Chapter 5: Biological Diversity and Conservation
Unit 3: The Life of a Cell
Chapter 6: The Chemistry of Life
Chapter 7: A View of the Cell
Chapter 8: Cellular Transport and the Cell Cycle
Chapter 9: Energy in a Cell
Unit 4: Genetics
Chapter 10: Mendel and Meiosis
Chapter 11: DNA and Genes
Chapter 12: Patterns of Heredity and Human Genetics
Chapter 13: Genetic Technology
Unit 5: Change Through Time
Chapter 14: The History of Life
Chapter 15: The Theory of Evolution
Chapter 16: Primate Evolution
Chapter 17: Organizing Life’s Diversity
Unit 6: Viruses, Bacteria, Protists, and Fungi
Chapter 18: Viruses and Bacteria
Chapter 19: Protists
Chapter 20: Fungi
Unit 7: Plants
Chapter 21:
Chapter 22:
Chapter 23:
Chapter 24:
What Is a Plant?
The Diversity of Plants
Plant Structure and Function
Reproduction in Plants
Unit 8: Invertebrates
Chapter 25: What Is an Animal?
Chapter 26: Sponges, Cnidarians, Flatworms, and
Roundworms
Chapter 27: Mollusks and Segmented Worms
Chapter 28: Arthropods
Chapter 29: Echinoderms and Invertebrate
Chordates
Unit 9: Vertebrates
Chapter 30: Fishes and Amphibians
Chapter 31: Reptiles and Birds
Chapter 32: Mammals
Chapter 33: Animal Behavior
Unit 10: The Human Body
Chapter 34: Protection, Support, and Locomotion
Chapter 35: The Digestive and Endocrine Systems
Chapter 36: The Nervous System
Chapter 37: Respiration, Circulation, and Excretion
Chapter 38: Reproduction and Development
Chapter 39: Immunity from Disease
The Life of a Cell
The Chemistry of Life
A View of the Cell
Cellular Transport and the Cell Cycle
Energy in a Cell
Chapter 9 Energy in a Cell
9.1: The Need for Energy
9.1: Section Check
9.2: Photosynthesis: Trapping the Sun’s Energy
9.2: Section Check
9.3: Getting Energy to Make ATP
9.3: Section Check
Chapter 9 Summary
Chapter 9 Assessment
What You’ll Learn
You will recognize why organisms need a
constant supply of energy and where that
energy comes from.
You will identify how cells store and release
energy as ATP.
You will describe the pathways by which
cells obtain energy.
What You’ll Learn
You will compare ATP
production in
mitochondria and in
chloroplasts.
Section Objectives:
• Explain why organisms need a supply of
energy.
• Describe how energy is stored and released
by ATP.
Cell Energy
• All living organisms must be able to obtain
energy from the environment in which they
live.
• Plants and other green organisms are able to
trap the light energy in sunlight and store it
in the bonds of certain molecules for later
use.
Cell Energy
• Other organisms cannot use sunlight directly.
• They eat green
plants. In that
way, they
obtain the
energy stored
in plants.
Work and the need for energy
• Active transport, cell division, movement of
flagella or cilia, and the production,
transport, and storage of proteins are some
examples of cell processes that require
energy.
• There is a molecule in your cells that is a
quick source of energy for any organelle in
the cell that needs it.
Work and the need for energy
• The name of this energy molecule is
adenosine triphosphate or ATP for short.
• ATP is composed of an adenosine molecule
with three phosphate groups attached.
Forming and Breaking Down ATP
• The charged phosphate groups act like the
positive poles of two magnets.
• Bonding three phosphate groups to form
adenosine triphosphate requires considerable
energy.
Forming and Breaking Down ATP
• When only one phosphate group bonds, a
small amount of energy is required and the
chemical bond does not store much energy.
This molecule is called adenosine
monophosphate (AMP).
• When a second phosphate group is added,
more energy is required to force the two
groups together. This molecule is called
adenosine diphosphate, or ADP.
Forming and Breaking Down ATP
• An even greater amount of energy is required
to force a third charged phosphate group
close enough to the other two to form a
bond. When this bond is broken, energy is
released.
Forming and Breaking Down ATP
• The energy of ATP becomes available to a
cell when the molecule is broken down.
Adenosine
P
P
P
Adenosine triphosphate (ATP)
P
P
Adenosine diphosphate (ADP)
Adenosine
P
P
How cells tap into the energy stored in ATP
• When ATP is broken down and the energy is
released, the energy must be captured and
used efficiently by cells.
• Many proteins have a specific site where
ATP can bind.
How cells tap into the energy stored in ATP
• Then, when the
phosphate bond is
broken and the energy
released, the cell can
use the energy for
activities such as
making a protein or
transporting molecules
through the plasma
membrane.
ATP
Protein
P
ADP
ADP
Energy
How cells tap into the energy stored in ATP
• When ATP has been broken down to ADP,
the ADP is released from the binding site in
the protein and the binding site may then be
filled by another ATP molecule.
Question 1
What is the primary difference in the ways
that plants and animals obtain energy?
Answer
All living organisms need energy. Plants can
trap light energy in sunlight and store it for
later use. Animals cannot trap energy from
sunlight and must eat plants that contain
stored energy.
Question 2
Why does the formation of ATP require
energy?
One molecule of ATP contains three phosphate
groups, which are charged particles. Energy is
required to bond the phosphate groups onto
the same molecule because they behave the
same way that the poles of magnets do and
repel groups with like charges. When the ATP
molecule is broken down, the chemical energy
stored in it becomes available to the cell for
life processes.
Question 3
A molecule of adenosine that has one
phosphate group bonded to it is ______.
A. AMP
B. ADP
C. ATP
D. ACP
The answer is A. AMP is adenosine
monophosphate.
Adenosine
P
P
P
Adenosine triphosphate (ATP)
P
P
Adenosine diphosphate (ADP)
Adenosine
P
P
The addition and release
of a phosphate group on
adenosine diphosphate
creates a cycle of ATP
formation and
breakdown.
Question 4
What is the function of the protein molecule
shown in this diagram?
ATP
Protein
P
ADP
ADP
Energy
This protein molecule has a specific binding site
for ATP. In order to access the energy stored
ATP, the protein molecule binds the ATP and
uncouples one phosphate group. This action
releases energy that is then available to the cell.
ATP
Protein
P
ADP
ADP
Energy
Section Objectives:
• Relate the structure of chloroplasts to the
events in photosynthesis.
• Describe light-dependent reactions.
• Explain the reactions and products of the
light-independent Calvin cycle.
Trapping Energy from Sunlight
• The process that uses the sun’s energy to
make simple sugars is called photosynthesis.
Trapping Energy from Sunlight
• Photosynthesis happens in two phases.
1. The light-dependent reactions convert light
energy into chemical energy.
2. The molecules of ATP produced in the lightdependent reactions are then used to fuel the
light-independent reactions that produce simple
sugars.
• The general equation for photosynthesis is
written as 6CO2 + 6H2O→C6H12O6 + 6O2
Trapping Energy from Sunlight
Click image to view movie.
The chloroplast and pigments
• To trap the energy in the sun’s light, the
thylakoid membranes contain pigments,
molecules that absorb specific wavelengths
of sunlight.
• Although a photosystem contains several
kinds of pigments, the most common is
chlorophyll.
• Chlorophyll absorbs most wavelengths of
light except green.
Light-Dependent Reactions
• As sunlight strikes the chlorophyll molecules
in a photosystem of the thylakoid membrane,
the energy in the light is transferred to
electrons.
• These highly energized, or excited, electrons
are passed from chlorophyll to an electron
transport chain, a series of proteins
embedded in the thylakoid membrane.
Sun
Light-Dependent
Reactions
• At each step along
the transport
chain, the
electrons lose
energy.
Light energy transfers to chlorophyll.
Chlorophyll passes energy down through the
electron transport chain.
Energized electrons provide energy that
splits
H2 O
H+
NADP+
bonds P to ADP
forming
oxygen
ATP
released
NADPH
for the use in
light-independent reactions
Light-Dependent Reactions
• This “lost” energy can be used to form ATP
from ADP, or to pump hydrogen ions into the
center of the thylakoid disc.
• Electrons are re-energized in a second
photosystem and passed down a second
electron transport chain.
Light-Dependent Reactions
• The electrons are transferred to the stroma of
the chloroplast. To do this, an electron
carrier molecule called NADP is used.
• NADP can combine with two excited
electrons and a hydrogen ion (H+) to become
NADPH.
• NADPH will play an important role in the
light-independent reactions.
Restoring electrons
• To replace the lost electrons, molecules of
water are split in the first photosystem. This
reaction is called photolysis.
Sun
Chlorophyll
H2O + + _12 O2 + 2e-
2e-
_1 O + 2H+
2
2
H2O
Restoring electrons
• The oxygen produced by photolysis is
released into the air and supplies the oxygen
we breathe.
• The electrons are returned to chlorophyll.
• The hydrogen ions are pumped into the
thylakoid, where they accumulate in high
concentration.
(CO2)
The Calvin
Cycle
(Unstable intermediate)
(RuPB)
ADP +
ATP
ATP
ADP +
NADPH
NADP+
(PGAL)
(PGAL)
(Sugars and other carbohydrates)
(PGAL)
The Calvin Cycle
• Carbon fixation The carbon atom from CO2
bonds with a five-carbon sugar called ribulose
biphosphate (RuBP) to form an unstable six(CO )
carbon sugar.
2
• The stroma in
chloroplasts
hosts the Calvin
cycle.
(RuBP)
The Calvin Cycle
• Formation of 3carbon molecules
The six-carbon
sugar formed in
Step A
immediately
splits to form two
three-carbon
molecules.
(Unstable intermediate)
The Calvin Cycle
• Use of ATP and NADPH
A series of reactions
involving ATP and
NADPH from the lightdependent reactions
converts the three-carbon
molecules into
phosphoglyceraldehyde
(PGAL), three-carbon
sugars with higher energy
bonds.
ATP
ADP +
NADPH
NADP+
(PGAL)
The Calvin Cycle
• Sugar production One
out of every six
molecules of PGAL is
transferred to the
cytoplasm and used in
the synthesis of sugars
and other carbohydrates.
After three rounds of the
cycle, six molecules of
PGAL are produced.
(PGAL)
(Sugars and other carbohydrates)
The Calvin Cycle
• RuBP is replenished
Five molecules of
PGAL, each with
three carbon atoms,
produce three
molecules of the
five-carbon RuBP.
This replenishes the
RuBP that was used
up, and the cycle can
continue.
ADP+ P
ATP
(PGAL)
Question 1
The process that uses the sun’s energy to make
simple sugars is ________.
A. cellular respiration
B. glycolysis
C. photosynthesis
D. photolysis
The answer is C. Photosynthesis happens in
two phases to make simple sugars and convert
the sugars into complex carbohydrates for
energy storage.
Question 2
The function accomplished by the lightdependent reactions is ________.
A. energy storage
B. sugar production
C. carbon fixation
D. conversion of sugar to PGAL
The answer is A. The
light-dependent
reactions transfer
energy from the sun to
chlorophyll, and pass
energized electrons to
proteins embedded in
the thylakoid
membrane for storage
in ATP and NADPH
molecules.
Sun
Light energy transfers to chlorophyll.
Chlorophyll passes energy down through the
electron transport chain.
Energized electrons provide energy that
splits
H2 O
H+
NADP+
bonds P to ADP
forming
oxygen
ATP
released
NADPH
for the use in
light-independent reactions
Question 3
The first step in the Calvin cycle is the ________.
A. replenishing of ribulose biphosphate
B. production of phosphoglyceraldehyde
C. Splitting of six-carbon sugar into two
three-carbon molecules
D. Bonding of carbon to ribulose
biphosphate
The answer is D. The carbon atom from CO2
bonds with a five-carbon sugar to form an
unstable six-carbon sugar. This molecule then
splits to form two three-carbon molecules.
Question 4
How many rounds of the Calvin cycle must
occur in order for one molecule of PGAL to
be transferred to the cell’s cytoplasm?
A. 1
B. 2
C. 3
D. 4
The answer is C. Each round of the Calvin
cycle produces two molecules of PGAL.
Section Objectives:
• Compare and contrast cellular respiration and
fermentation.
• Explain how cells obtain energy from
cellular respiration.
Cellular Respiration
• The process by which mitochondria break
down food molecules to produce ATP is
called cellular respiration.
• There are three stages of cellular respiration:
glycolysis, the citric acid cycle, and the
electron transport chain.
Cellular Respiration
• The first stage, glycolysis, is anaerobic—no
oxygen is required.
• The last two stages are aerobic and require
oxygen to be completed.
Glycolysis
• Glycolysis is a series of chemical reactions in
the cytoplasm of a cell that break down glucose,
a six-carbon compound, into two molecules of
pyruvic acid, a three-carbon compound.
4ATP
2ATP
Glucose
2ADP
4ADP + 4P
2PGAL
2 Pyruvic
acid
2NAD+
2NADH + 2H+
Glycolysis
• Glycolysis is not very effective, producing
only two ATP molecules for each glucose
molecule broken down.
4ATP
2ATP
Glucose
2ADP
4ADP + 4P
2PGAL
2 Pyruvic
acid
2NAD+
2NADH + 2H+
Glycolysis
• Before citric acid cycle and electron transport chain can
begin, pyruvic acid undergoes a series of reactions in
which it gives off a molecule of CO2 and combines with
a molecule called coenzyme A to form acetyl-CoA.
Mitochondrial
membrane
Outside the
mitochondrion
Pyruvic
acid
CO2
Inside the
mitochondrion
Pyruvic
acid
Coenzyme A
Intermediate
by-product NAD+
- CoA
Acetyl-CoA
NADH + H+
The citric acid cycle
• The citric acid cycle, also called the Krebs
cycle, is a series of chemical reactions
similar to the Calvin cycle in that the
molecule used in the first reaction is also
one of the end products.
• For every turn of the cycle, one molecule of
ATP and two molecules of carbon dioxide
are produced.
The Citric
Acid Cycle
(Acetyl-CoA)
NADH +
H+
NAD+
The
mitochondria
host the citric
acid cycle.
Oxaloacetic acid
Citric acid
NAD+
NADH + H+
O=
=O
(CO2)
Citric
Acid
Cycle
NAD+
NADH + H+
O=
=O
ADP +
ATP
FADH2 FAD
(CO2)
• Citric acid The
two-carbon
compound acetylCoA reacts with a
four-carbon
compound called
oxaloacetic acid to
form citric acid, a
six-carbon
molecule.
The citric acid cycle
Acetyl-CoA
Oxaloacetic acid
Citric acid
• Formation of CO2 The citric acid cycle
A molecule of CO2
NAD
is formed,
NADH + H
reducing the
O=
=O
eventual product
(CO )
to a five-carbon
compound. In the
process, a
molecule of
NADH and H+ is
produced.
+
+
2
• Formation of the
second CO2
Another molecule
of CO2 is released,
forming a fourcarbon compound.
One molecule of
ATP and a
molecule of
NADH are also
produced.
The citric acid cycle
NAD+
NADH + H+
O=
=O
ADP +
(CO2)
ATP
• Recycling of
The citric acid cycle
oxaloacetic acid The
four-carbon molecule
goes through a series
of reactions in which
NADH + H
FADH2, NADH, and
NAD
+
H are formed. The
carbon chain is
FADH FAD
rearranged, and
oxaloacetic acid is
again made available
for the cycle.
+
+
2
The electron transport chain
• In the electron transport chain, the carrier
molecules NADH and FADH2 gives up
electrons that pass through a series of reactions.
Oxygen is the final electron acceptor.
Electron carrier
proteins
Space between
inner and outer
membranes
Enzyme
Inner membrane
e-
Electron
pathway
NADH
NAD+
FADH2
FAD
4H+ + O2
+ 4 electrons
H2O
ADP +
H2O
ATP
Center of
mitochondrion
The electron transport chain
• Overall, the electron transport chain adds 32
ATP molecules to the four already produced.
Fermentation
• During heavy exercise, when your cells are
without oxygen for a short period of time, an
anaerobic process called fermentation
follows glycolysis and provides a means to
continue producing ATP until oxygen is
available again.
Lactic acid fermentation
• Lactic acid fermentation is one of the
processes that supplies energy when oxygen
is scarce.
• In this process, the reactions that produced
pyruvic acid are reversed.
• Two molecules of pyruvic acid use NADH
to form two molecules of lactic acid.
Lactic acid fermentation
• This releases NAD+ to be used in glycolysis,
allowing two ATP molecules to be formed
for each glucose molecule.
• The lactic acid is transferred from muscle
cells, to the liver that converts it back to
pyruvic acid.
Alcoholic fermentation
• Another type of fermentation, alcoholic
fermentation, is used by yeast cells and some
bacteria to produce CO2 and ethyl alcohol.
Comparing Photosynthesis and
Cellular Respiration
Table 9.1 Comparison of Photosynthesis and Cellular Respiration
Photosynthesis
Cellular Respiration
Food synthesized
Energy from sun stored in glucose
Food broken down
Energy of glucose released
Carbon dioxide taken in
Carbon dioxide given off
Oxygen given off
Oxygen taken in
Produces sugars from PGAL
Produces CO2 and H2O
Requires light
Does not require light
Occurs only in presence of
chlorophyll
Occurs in all living cells
Question 1
What do the Calvin cycle and the Citric acid
cycle have in common?
A. The molecule used in the first reaction is
also one of the end products.
B. Both require input of ATP molecules.
C. Both generate ADP.
D. From every turn of the cycle, two
molecules of carbon dioxide are produced.
The answer is A. In the Calvin cycle, RuBP
bonds to carbon in the first step and is
produced in the last step. In the citric acid
cycle, oxaloacetic acid reacts in the first step
and is recycled in the last step.
Question 2
The process by which mitochondria break
down food molecules to produce ATP is
called ________.
A. photosynthesis
B. cellular respiration
C. the light-independent reaction
D. the Calvin cycle
The answer is B. Photosynthesis, lightindependent reactions, and the Calvin
cycle all occur in plants.
Question 3
The three stages of cellular respiration are
________.
A. glycolysis, the Calvin cycle, and the electron
transport chain
B. carbon fixation, the citric acid cycle, and the
electron transport chain
Question 3
The three stages of cellular respiration are
________.
C. glycolysis, the citric acid cycle, and the
electron transport chain
D. the light-dependent reactions, the citric
acid cycle and the electron transport chain
The answer is C. The first stage is anaerobic,
but the last two stages require oxygen to be
completed.
Question 4
Which of the following yields the greatest net
ATP?
A. Lactic acid fermentation
B. Alcoholic fermentation
C. Calvin cycle
D. Cellular respiration
The answer is D. Cellular respiration is far
more efficient in ATP production than the
fermentation reactions.
Comparison of Fermentation to Cellular Respiration
Lactic Acid
glucose
glycolysis (pyruvic acid)
Alcoholic
Cellular respiration
glucose
glucose
glycolysis (pyruvic acid)
glycolysis (pyruvic acid)
carbon dioxide
carbon dioxide
lactic acid
alcohol
water
2 ATP
2 ATP
38 ATP
The Need for Energy
• ATP is the molecule that stores energy for easy
use within the cell.
• ATP is formed when a phosphate group is added
to ADP. When ATP is broken down, ADP and
phosphate are formed and energy is released.
• Green organisms trap the energy in
sunlight and store it in the bonds of certain
molecules for later use.
The Need for Energy
• Organisms that cannot
use sunlight directly
obtain energy by
consuming plants or
other organisms that
have consumed plants.
Photosynthesis: Trapping the Sun’s Energy
• Photosynthesis is the process by which cells use
light energy to make simple sugars.
• Chlorophyll in the chloroplasts of plant cells
traps light energy needed for photosynthesis.
• The light reactions of photosynthesis
produce ATP and result in the splitting of
water molecules.
Photosynthesis: Trapping the Sun’s Energy
• The reactions of the Calvin Cycle make
carbohydrates using CO2 along with ATP
and NADPH from the light reactions.
Getting Energy to Make ATP
• In cellular respiration, cells break down
carbohydrates to release energy.
• The first stage of cellular respiration,
glycolysis, takes place in the cytoplasm
and does not require oxygen.
• The citric acid cycle takes place in
mitochondria and requires oxygen.
Question 1
Name two differences between
photosynthesis and cellular respiration.
Although both processes use electron carriers
and form ATP, they accomplish quite different
tasks as shown in the table.
Table 9.1 Comparison of Photosynthesis and Cellular Respiration
Photosynthesis
Cellular Respiration
Food synthesized
Energy from sun stored in glucose
Food broken down
Energy of glucose released
Carbon dioxide taken in
Carbon dioxide given off
Oxygen given off
Oxygen taken in
Produces sugars from PGAL
Produces CO2 and H2O
Requires light
Does not require light
Occurs only in presence of
chlorophyll
Occurs in all living cells
Question 2
Choose the word from this list that does NOT
belong with the others.
A. oxaloacetic acid
B. FADH2
C. Acetyl-CoA
D. ribulose biphosphate
The answer is D. RuBP is utilized in the Calvin
cycle; the others are part of the citric acid cycle.
Question 3
Six molecules of glucose would give a net
yield of _____ ATP following glycolysis.
A. 8
B. 16
C. 6
D. 12
The answer is D. Glycolysis produces two
ATP molecules for each glucose molecule
broken down.
Question 4
In which of the following structures do the
light-dependent reactions of photosynthesis
take place?
A.
C.
B.
D.
The answer is D. The light-dependent reactions
of photosynthesis take place in the thylakoid
membranes of chloroplasts.
Question 5
In which stage of photosynthesis is carbon
from CO2 used to form a six-carbon sugar?
A. Calvin cycle
B. glycolysis
C. citric acid cycle
D. electron transport chain
The
answer
is A.
(CO2)
(Unstable intermediate)
(RuPB)
ADP +
ATP
ATP
ADP +
NADPH
NADP+
(PGAL)
(PGAL)
(Sugars and other carbohydrates)
(PGAL)
Question 6
What component of thylakoid membranes
absorbs specific wavelengths of sunlight?
A. electrons
B. pigments
C. chloroplasts
D. mitochondria
The answer is B. Pigments are arranged within
the thylakoid membranes in photosystems; the
most common pigment is chlorophyll.
Question 7
Which of the following is a product of
cellular respiration?
A. lactic acid
B. alcohol
C. glucose
D. carbon dioxide
The answer is D. Carbon dioxide, water, and
ATP are the products of cellular respiration.
Question 8
Complete the concept map using the following
terms: RuBP replenishing, formation of 3-carbon
molecules, Calvin cycle, carbon fixation.
1
2
3
are steps in
4
which takes place in stroma
Completed concept map should reflect carbon
fixation, RuBP replenishing, and formation of
3-carbon molecules as steps in the Calvin cycle
which takes place in stroma.
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End of Chapter 9 Show