Chapter 8 Cellular Energy
Section 1: How Organisms Obtain Energy
Section 2: Photosynthesis
Section 3: Cellular Respiration
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• Big Idea
– Photosynthesis converts the Sun’s energy into
chemical energy, while cellular respiration uses
chemical energy to carry out life function.
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Chapter 8
Cellular Energy
8.1 How Organisms Obtain Energy
All living organisms use energy to carry out all
biological processes
Macromolecules are assembled and broken
down, substances are transported across cell
membranes, and genetic instructions are
transmitted.
All of these cellular activities require energy.
Chapter 8
Cellular Energy
8.1 How Organisms Obtain Energy
Transformation of Energy
 Energy is the ability to do work.
 Thermodynamics is the study of the flow and
transformation of energy in the universe.
Chapter 8
Cellular Energy
8.1 How Organisms Obtain Energy
Laws of Thermodynamics
 First law— (Law of conservation of energy)
energy can be converted from one form to
another, but it cannot be created nor
destroyed.
 Examples:
Food is converted to chemical energy
when you eat
Mechanical energy when you run or kick a
ball
Chapter 8
Cellular Energy
8.1 How Organisms Obtain Energy
Laws of Thermodynamics
 Second law—energy cannot be converted
without the loss of usable energy.
“loss” energy is generally converted to
thermal energy
Increases Entropy
Chapter 8
Cellular Energy
8.1 How Organisms Obtain Energy
Laws of Thermodynamics
 Entropy –
The measure of disorder (or unusable
energy) in a system
Chapter 8
Cellular Energy
8.1 How Organisms Obtain Energy
Autotrophs and Heterotrophs
 Nearly all the energy for life comes from the
Sun
Chapter 8
Cellular Energy
8.1 How Organisms Obtain Energy
Autotrophs and Heterotrophs
 Autotrophs are organisms that make their
own food.
Chapter 8
Cellular Energy
8.1 How Organisms Obtain Energy
Autotrophs and Heterotrophs
 Autotrophs are organisms that make their
own food.
 Examples:
Chemoautotrophs use inorganic
substances such as hydrogen sulfide as a
source of energy
Photoautotrophs (like plants) convert light
energy from the Sun into chemical energy.
Chapter 8
Cellular Energy
8.1 How Organisms Obtain Energy
Autotrophs and Heterotrophs
 Heterotrophs are organisms that need to
ingest food to obtain energy.
 Examples:
Aphid
Lady bug
Chapter 8
Cellular Energy
8.1 How Organisms Obtain Energy
Metabolism
 All of the chemical reactions in a cell
 Photosynthesis—light energy from the Sun is
converted to chemical energy for use by the
cell
 Cellular respiration—organic molecules are
broken down to release energy for use by
the cell
Chapter 8
Cellular Energy
8.1 How Organisms Obtain Energy
Metabolism
 Metabolic Pathway –
Series of chemical reactions in which the
product of one reaction is the substrate for
the next reaction
Examples:
Catabolic pathways
Anabolic pathways
Chapter 8
Cellular Energy
8.1 How Organisms Obtain Energy
Metabolism
 Metabolic Pathway –
Examples:
Catabolic pathways
Release energy by breaking down
larger molecules into smaller
molecules
Chapter 8
Cellular Energy
8.1 How Organisms Obtain Energy
Metabolism
 Metabolic Pathway –
Examples:
Anabolic pathways
Use the energy released by catabolic
pathways to build larger molecules
from smaller molecules
Chapter 8
Cellular Energy
8.1 How Organisms Obtain Energy
Photosynthesis
 Photosynthesis is the anabolic pathway in
which light energy from the Sun is converted to
chemical energy for use by the cell.
Autotrophs use light energy, carbon dioxide,
and water to form glucose and oxygen
Chapter 8
Cellular Energy
8.1 How Organisms Obtain Energy
Cellular Respiration
 Cellular Respiration is the catabolic pathway in
which organic molecules are broken down to
release energy for use by the cell.
Oxygen is used to break down organic
molecules, resulting in the production of
carbon dioxide and water
Chapter 8
Cellular Energy
8.1 How Organisms Obtain Energy
ATP: The Unit of Cellular Energy
 ATP (Adenosine Triphosphate)
releases energy when the
bond between the second and
third phosphate groups is
broken, forming a molecule
called adenosine diphosphate
(ADP) and a free phosphate
group.
Chapter 8
Cellular Energy
8.1 How Organisms Obtain Energy
ATP: The Unit of Cellular Energy
 ATP structure
A nucleotide made of an
adenine base, a ribose
sugar, and three phosphate
group
Chapter 8
Cellular Energy
8.1 How Organisms Obtain Energy
ATP: The Unit of Cellular Energy
 ATP function
ATP releases energy when
the bond between the
second and third phosphate
groups is broken, forming a
molecule called adenosine
diphosphate (ADP) and a
free phosphate group
Chapter 8
Cellular Energy
8.2 Photosynthesis
Main Idea: light energy is trapped and
converted into chemical energy during
photosynthesis
• Photo – means “light”
• Synthesis – means “to create”
Chapter 8
Cellular Energy
8.2 Photosynthesis
Most autotrophs – including plants – make
organic compounds, such as sugars, by a
process called photosynthesis
Chapter 8
Cellular Energy
8.2 Photosynthesis
Overview of Photosynthesis
 Photosynthesis occurs in two phases.
 Light-dependent reactions
 Light-independent reactions
Chapter 8
Cellular Energy
8.2 Photosynthesis
Phase One: Light Reactions (Light –
Dependent Reaction)
 The absorption of light is the first step in
photosynthesis.
 Light energy is absorbed and then transformed
into chemical energy in the form of ATP and
NADPH
Chapter 8
Cellular Energy
8.2 Photosynthesis
Phase One: Light Reactions (Light –
Dependent Reaction)
 Chloroplasts large organelles that capture light
energy.
Chapter 8
Cellular Energy
8.2 Photosynthesis
Phase One: Light Reactions (Light –
Dependent Reaction)
 Chloroplasts are mainly found in the cells of
leaves in plants.
Chapter 8
Cellular Energy
8.2 Photosynthesis
Phase One: Light Reactions (Light –
Dependent Reaction)
 Thylakoids are flattened saclike membranes
that arranged in stacks called grana.
Chapter 8
Cellular Energy
8.2 Photosynthesis
Phase One: Light Reactions (Light –
Dependent Reaction)
 Stroma is the fluid- filled space outside the
grana
Chapter 8
Cellular Energy
8.2 Photosynthesis
Phase One: Light Reactions (Light –
Dependent Reaction)
 Pigments are light-absorbing molecules found
in the thylakoid membranes of chloroplasts
Chapter 8
Cellular Energy
8.2 Photosynthesis
Phase One: Light Reactions (Light –
Dependent Reaction)
 Chlorophyll is the major light – absorbing
pigment in plants.
 Two types of chlorophyll:
Chlorophyll a
Chlorophyll b
 Accessory pigments called carotenoids
produce the color of carrots and sweet
potatoes
Chapter 8
Cellular Energy
8.2 Photosynthesis
Electron Transport
 Light energy excites electrons in
photosystem II and also causes a water
molecule to split, releasing an electron into
the electron transport system, H+ into the
thylakoid space, and O2 as a waste product.
Chapter 8
Cellular Energy
8.2 Photosynthesis
 The excited electrons move from
photosystem II to an electron-acceptor
molecule in the thylakoid membrane.
 The electron-acceptor molecule transfers the
electrons along a series of electron-carriers
to photosystem I.
Chapter 8
Cellular Energy
8.2 Photosynthesis
 Photosystem I transfers the electrons to a
protein called ferrodoxin.
 Ferrodoxin transfers the electrons to the
electron carrier NADP+, forming the energystoring molecule NADPH.
The Light Reaction
Light Reactions
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Chapter 8
Cellular Energy
8.2 Photosynthesis
Phase Two: The Calvin Cycle (Light –
Independent Reaction)
 In the second
phase of
photosynthesis,
called the Calvin
cycle, energy is
stored in organic
molecules such
as glucose.
Chapter 8
Cellular Energy
8.2 Photosynthesis
Phase Two: The Calvin Cycle (Light –
Independent Reaction)
 The ATP and
NADPH that
were formed in
phase one are
used to make
glucose
Chapter 8
Cellular Energy
8.2 Photosynthesis
Phase Two: The Calvin Cycle (Light –
Independent Reaction)
Chapter 8
Cellular Energy
8.2 Photosynthesis
 1st Step (Carbon Fixation) - Six CO2 molecules
combine with six 5-carbon compounds to form
twelve 3-carbon molecules called 3-PGA.
 2nd Step (Reduction) - The chemical energy
stored in ATP and NADPH is transferred to the
3-PGA molecules to form high-energy
molecules called (glyceraldehyde 3phosphate) G3P.
Chapter 8
Cellular Energy
8.2 Photosynthesis
 3rd Step - Two G3P molecules leave the cycle
to be used for the production of glucose and
other organic compounds.
 Final Step (Regeneration of RuBP)- An
enzyme called rubisco converts the remaining
ten G3P molecules into 5-carbon molecules
called RuBP. These molecules combine with
new carbon dioxide molecules to continue the
cycle.
Chapter 8
Cellular Energy
8.2 Photosynthesis
Alternative Pathways
 C4 plants
 CAM plants
Chapter 8
Cellular Energy
8.3 Cellular Respiration
Overview of Cellular Respiration
 Organisms obtain energy in a process called
cellular respiration.
 The equation for cellular respiration is the
opposite of the equation for photosynthesis.
Chapter 8
Cellular Energy
8.3 Cellular Respiration
 Cellular respiration occurs in two main parts.
 Glycolysis
 Aerobic respiration
Chapter 8
Cellular Energy
8.3 Cellular Respiration
Glycolysis
 Glucose is broken down in the cytoplasm
through the process of glycolysis.
Chapter 8
Cellular Energy
8.3 Cellular Respiration
Glycolysis
 Two molecules of ATP and two molecules
of NADH are formed for each molecule of
glucose that is broken down.
 Two molecules of ATP are required to start
the reactions that will produce energy for
the cell
Chapter 8
Cellular Energy
8.3 Cellular Respiration
Glycolysis
• 2 phosphate groups are joined to glucose (the 2 Phosphate
groups are derived from 2 molecules of ATP)
• The 6-Carbon molecule of Glucose is broken into two 3-Carbon
compounds
• Two Phosphate groups are added and electrons and hydrogen
ions (H+) combine with two NAD+ molecules to form NADH
molecules
• Keep in mind that NAD+ is an electron carrier that is similar to
NADP (an electron carrier used during photosynthesis)
• The two 3-Carbon compounds are converted into two molecules
of pyruvate
• At the same time 4 molecules of ATP are produced
Chapter 8
Cellular Energy
8.3 Cellular Respiration
Glycolysis
 Glycolysis has a net result of two ATP and
two pyruvate.
Chapter 8
Cellular Energy
8.3 Cellular Respiration
Krebs Cycle
 Also known as the tricarboxylic acid (TCA)
cycle
 Also known as the citric acid cycle
Chapter 8
Cellular Energy
8.3 Cellular Respiration
Krebs Cycle
 Most of the energy from the glucose is still
contained in the pyruvate.
 The series of reactions in which pyruvate is
broken down into carbon dioxide is called the
Krebs cycle.
 When oxygen is present, pyruvate is
transported into the mitochondrial matrix
Chapter 8
Cellular Energy
8.3 Cellular Respiration
• Begins with acetyl CoA
combining with a 4-Carbon
compound to form a 6 – Carbon
compound known as citric acid
• Citric acid is then broken down in
the next series of steps,
releasing 2 molecules of carbon
dioxide and generating one ATP,
three NADH, and one FADH2.
FAD is another electron carrier
similar to NAD+ and NADP+
• Acetyl CoA and citric acid are
generated and the cycle
continues.
Chapter 8
Cellular Energy
8.3 Cellular Respiration
Before the Krebs Cycle
 Pyruvate first reacts with coenzyme A (CoA)
to form a 2-Carbon intermediate called acetyl
CoA.
 At the same time NAD+ is converted to
NADH and carbon dioxide is released.
 Acetyl CoA then moves to the mitochondria
matrix. 2 CO2 and 2NADH are produced.
Chapter 8
Cellular Energy
8.3 Cellular Respiration
 Two molecules of
pyruvate are formed
during glycolysis. This
means that there are
two “turns” of the
Krebs Cycle for each
glucose molecule.
Chapter 8
Cellular Energy
8.3 Cellular Respiration
 The net yield from the
Krebs cycle is six CO2
molecules, two ATP,
eight NADH, and two
FADH2.
Chapter 8
Cellular Energy
8.3 Cellular Respiration
Electron Transport
 Final step in the breakdown of glucose
 Point at which ATP is produced
 Produces 24 ATP
Chapter 8
Cellular Energy
8.3 Cellular Respiration
Electron Transport
• The final step in the breakdown of glucose.
• Point where most ATP is produced
• Electrons and hydrogen ions from NADH and FADH2
produced in Krebs Cycle are used to convert ADP to ATP.
• Electrons move along mitochondrial membrane from one
protein to another.
• H+ ions are pumped into the mitochondrial matrix across
the inner mitochondrial membrane.
• Those H+ ions then diffuse through ATP synthase into the
mitochondrial matrix. This process converts ADP to ATP
in a process called chemiosmosis
Chapter 8
Cellular Energy
8.3 Cellular Respiration
Electron Transport
• Similarities and Differences in Electron Transport in
Photosynthesis and Cellular Respiration
Photosynthesis
Cellular Respiration
Chapter 8
Cellular Energy
8.3 Cellular Respiration
Some Prokaryotes
• Aerobic organisms that undergo aerobic respiration, but
because they do not have mitochondria, they use the
plasma membrane as the location of the electron
transport.
• Anaerobic organism that grow and reproduce without
oxygen.
• ATP is produced through glycolysis
Chapter 8
Cellular Energy
8.3 Cellular Respiration
Anaerobic Respiration
 The anaerobic pathway that follows glycolysis
 One type is fermentation
 Two main types
 Lactic acid fermentation
 Alcohol fermentation
Cellular
Respiration
Chapter 8
Cellular Energy
8.3 Cellular Respiration
Fermentation
 Two main types
 Lactic acid fermentation – enzymes convert
the pyruvate in glycolysis to lactic acid
 Alcohol fermentation – type of fermentation
in which pyruvate is converted to ethyl
alcohol and carbon dioxide
Cellular
Respiration
Chapter 8
Cellular Energy
8.3 Cellular Respiration
How are photosynthesis and cellular respiration
related?
Cellular
Respiration
Chapter 8
Cellular Energy
Chapter Diagnostic
Questions
Which statement describes the law of
conservation of energy?
A. Energy cannot be
converted or destroyed.
B. Energy can be converted
and destroyed.
C. Energy can be converted
but not destroyed.
D. Energy can be destroyed
but not converted.
1.
2.
3.
4.
0%
A
0%
B
A
B
C
D
0%
C
0%
D
Chapter 8
Cellular Energy
Chapter Diagnostic
Questions
In which metabolic process are molecules
broken down to produce carbon dioxide and
water?
A. photosynthesis
B. cellular respiration
C. homeostasis
D. fermentation
1.
2.
3.
4.
0%
A
0%
B
A
B
C
D
0%
C
0%
D
Chapter 8
Cellular Energy
Chapter Diagnostic
Questions
At the end of the Calvin cycle, where is energy
stored?
A. NADPH
B. ATP
C. chloroplast
D. glucose
1.
2.
3.
4.
0%
A
0%
B
A
B
C
D
0%
C
0%
D
Chapter 8
Cellular Energy
8.1 Formative
Questions
Which law of thermodynamics explains why the
ladybug receives the least amount of usable energy?
A
B
0%
B
0%
A
A. the first law of
thermodynamics
B. the second law of
thermodynamics
1.
2.
Chapter 8
Cellular Energy
8.1 Formative
Questions
All of the energy from the
food you eat comes from
the sun.
A. true
B. false
1.
2.
0%
B
A
0%
A
B
Chapter 8
Cellular Energy
8.1 Formative
Questions
Why is cellular respiration a catabolic pathway?
1.
2.
3.
4.
0%
C
0%
B
A
0%
A
B
C
D
0%
D
A. Energy is used to form
glucose and oxygen.
B. Energy is converted from
water to carbon dioxide.
C. Energy that is lost is
converted to thermal energy.
D. Energy is released by the
breakdown of molecules.
Chapter 8
Cellular Energy
8.1 Formative
Questions
Why is adenosine triphosphate (ATP) such an
important biological molecule?
1.
2.
3.
4.
A
B
C
D
0%
D
0%
C
0%
B
0%
A
A. It captures light energy
from the sun.
B. It is produced in anabolic
pathways.
C. It stores and releases
chemical energy.
D. It converts mechanical
energy to thermal energy.
Chapter 8
Cellular Energy
8.2 Formative
Questions
Where in the plant cell does
photosynthesis take place?
1.
2.
3.
4.
0%
C
0%
B
A
0%
A
B
C
D
0%
D
A. chloroplasts
B. Golgi apparatus
C. mitochondria
D. vacuoles
Chapter 8
Cellular Energy
8.2 Formative
Questions
Which range of
wavelengths is reflected
by chlorophylls a and b?
A. 400-500 nm
B. 500-600 nm
C. 600-700 nm
1.
2.
3.
0%
C
0%
B
A
0%
A
B
C
Chapter 8
Cellular Energy
8.2 Formative
Questions
Which mechanism of photosynthesis uses
the movement of hydrogen ions (H+) across
a concentration gradient to synthesize ATP?
1.
2.
3.
4.
0%
C
0%
B
A
0%
A
B
C
D
0%
D
A. absorption
B. chemiosmosis
C. electron transport
D. C2 pathway
Chapter 8
Cellular Energy
8.2 Formative
Questions
How are the C4 pathway and the CAM pathway
an adaptive strategy for some plants?
1.
2.
3.
4.
0%
C
0%
B
A
0%
A
B
C
D
0%
D
A. They accelerate
photosynthesis.
B. They release
more oxygen.
C. They help the plant
conserve water.
D. They reduce the
requirement for ATP.
Chapter 8
Cellular Energy
8.3 Formative
Questions
What is the overall purpose of cellular
respiration?
1.
2.
3.
4.
0%
C
0%
B
A
0%
A
B
C
D
0%
D
A. to make ATP
B. to process H2O
C. to store glucose
D. to deliver oxygen
Chapter 8
Cellular Energy
8.3 Formative
Questions
A
B
C
D
0%
C
B
A
1.
2.
3.
4.
0%
D
Which represents the general sequence of
cellular respiration?
A. TCA cycle 
chemiosmosis  glycolysis
B. glycolysis  Krebs
cycle  electron transport
C. electron absorption 
catalysis  phosphorylation
D. aerobic pathway 
anaerobic pathway 
0%
0%
fermentation
Chapter 8
Cellular Energy
8.3 Formative
Questions
Which stage of cellular respiration is the
anaerobic process?
1.
2.
3.
0%
B
A
0%
A
B
C
0%
C
A. glycolysis
B. Krebs cycle
C. electron transport
Chapter 8
Cellular Energy
8.3 Formative
Questions
Which molecule
generated by the Krebs
cycle is a waste product?
1.
2.
3.
4.
0%
C
0%
B
A
0%
A
B
C
D
0%
D
A. CoA
B. CO2
C. FADH2
D. NADH
Chapter 8
Cellular Energy
Chapter Assessment
Questions
Look at the following figure.
Which part of the chloroplast
is a sac-like membrane
arranged in stacks?
A. grana
B. stroma
C. thylakoids
D. Golgi apparatus
1.
2.
3.
4.
0%
D
0%
C
0%
B
A
0%
A
B
C
D
Chapter 8
Cellular Energy
Chapter Assessment
Questions
During the Krebs cycle,
pyruvate is broken down
into what compound?
A. H2O
B. O2
C. CO
D. CO2
1.
2.
3.
4.
0%
D
0%
C
0%
B
A
0%
A
B
C
D
Chapter 8
Cellular Energy
Chapter Assessment
Questions
Look at the following figure.
Which molecule is released
when ATP becomes ADP?
A. phosphate group
B. water molecule
C. ribose sugar
D. energy cells
1.
2.
3.
4.
0%
D
0%
C
0%
B
A
0%
A
B
C
D
Chapter 8
Cellular Energy
Standardized Test
Practice
Which metabolic process is photosynthesis?
A
1.
2.
A
B
B
0%
B
A
0%
Chapter 8
Cellular Energy
Standardized Test
Practice
At the beginning of photosynthesis, which
molecule is split to produce oxygen (O2) as
a waste product?
1.
2.
3.
4.
0%
C
0%
B
A
0%
A
B
C
D
0%
D
A. CO2
B. H2O
C. C6H12O6
D. 3-PGA
Chapter 8
Cellular Energy
Standardized Test
Practice
Which molecule helps
provide the energy
that drives this cycle?
A. 3-PGA
B. CO2
C. NADPH
D. rubisco
1.
2.
3.
4.
0%
D
0%
C
0%
B
A
0%
A
B
C
D
Chapter 8
Cellular Energy
Standardized Test
Practice
Which product of the
Calvin cycle is used for
the production of
glucose and other
organic compounds?
A. ADP
B. CO2
C. G3P
D. NADP+
1.
2.
3.
4.
0%
D
0%
C
0%
B
A
0%
A
B
C
D
Chapter 8
Cellular Energy
Standardized Test
Practice
What is the final step of cellular respiration?
A. O2 and H+ form H2O.
B. Electrons and H2O
generate ATP.
1.
2.
3.
4.
0%
0%
C
A
0%
B
D. NADH and FADH2
gain electrons.
A
B
C
D
0%
D
C. C6H12O6 is broken
down into CO2.
Chapter 8
Cellular Energy
Standardized Test
Practice
What prevents pyruvate from
entering the Krebs cycle and
instead results in this pathway?
A. a buildup of CO2
B. a lack of oxygen
C. an excess of
glucose
1.
2.
3.
4.
0%
0%
D
0%
C
A
0%
B
D. an increased
demand for ATP
A
B
C
D
Chapter 8
Cellular Energy
Standardized Test
Practice
Which is not a process that occurs in both
cellular respiration and glycolysis?
A. chemiosmosis
B. electron transport
C. glycolysis
D. production of G3P
1.
2.
3.
4.
0%
D
0%
C
0%
B
A
0%
A
B
C
D
Chapter 8
Cellular Energy
Glencoe Biology Transparencies
Chapter 8
Cellular Energy
Image Bank
Chapter 8
Cellular Energy
Vocabulary
Section 1
energy
thermodynamics
metabolism
Photosynthesis
cellular respiration
adenosine triphosphate (ATP)
Chapter 8
Cellular Energy
Vocabulary
Section 2
thylakoid
granum
stroma
pigment
NADP+
Calvin cycle
rubisco
Chapter 8
Cellular Energy
Vocabulary
Section 3
anaerobic process
aerobic respiration
aerobic process
glycolysis
Krebs cycle
fermentation
Chapter 8
Cellular Energy
Animation
 ATP
 The Calvin Cycle
 Visualizing Electron Transport
 The Krebs Cycle (Citric Acid Cycle)
Chapter 8
Cellular Energy
Chapter 8
Cellular Energy
Chapter 8
Cellular Energy