Chapter 8
Cellular Energy
8.1 How Organisms Obtain Energy
Autotrophs and Heterotrophs
 Autotrophs are organisms that make their
own food.
 Heterotrophs are organisms that need to
ingest food to obtain energy.
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
ATP: The Unit of Cellular Energy
 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.
ATP
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.
 Two molecules of ATP and two molecules
of NADH are formed for each molecule of
glucose that is broken down.
Chapter 8
Cellular Energy
8.3 Cellular Respiration
Krebs Cycle
 Glycolysis has a net result of two ATP and
two pyruvate.
 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.
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.
The Krebs Cycle
Chapter 8
Cellular Energy
8.3 Cellular Respiration
Electron Transport
 Final step in the breakdown of glucose
 Point at which ATP is produced
 Produces 34 ATP
Chapter 8
Cellular Energy
8.3 Cellular Respiration
Anaerobic Respiration
 The anaerobic pathway that follows glycolysis
 Two main types
 Lactic acid fermentation
 Alcohol fermentation
Energy in a Cell
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
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
Which mechanism of photosynthesis uses
the movement of hydrogen ions (H+) across
a concentration gradient to synthesize ATP?
A
B
C
D
0%
0%
D
0%
B
A
0%
1.
2.
3.
4.
C
A. absorption
B. chemiosmosis
C. electron transport
D. C2 pathway
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
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
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%
B
A
0%
0%
C
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
1.
2.
3.
4.
0%
B
A
0%
0%
C
D. an increased
demand for ATP
A
B
C
D
0%
D
C. an excess of
glucose
Chapter 8
Cellular Energy
Standardized Test
Practice
Which is not a process that occurs in both
cellular respiration and glycolysis?
1.
2.
3.
4.
0%
C
0%
B
A
0%
A
B
C
D
0%
D
A. chemiosmosis
B. electron transport
C. glycolysis
D. production of G3P