Chapter 8 Cellular Energy
Section 1: How Organisms Obtain Energy
Section 2: Photosynthesis
Section 3: Cellular Respiration
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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—energy can be converted from one
form to another, but it cannot be created nor
destroyed.
 Second law—energy cannot be converted
without the loss of usable energy.
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.
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
 The absorption of light is the first step in
photosynthesis.
 Chloroplasts capture light energy.
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.
Visualizing
Electron
Transport
Chapter 8
Cellular Energy
8.2 Photosynthesis
Phase Two: The Calvin Cycle
 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
 Six CO2 molecules combine with six 5-carbon
compounds to form twelve 3-carbon molecules
called 3-PGA.
 The chemical energy stored in ATP and
NADPH is transferred to the 3-PGA molecules
to form high-energy molecules called G3P.
Chapter 8
Cellular Energy
8.2 Photosynthesis
 Two G3P molecules leave the cycle to be used
for the production of glucose and other organic
compounds.
 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.
Rubisco
• Ribulose Biphosphate Carboxylase is an allosteric
enzyme involved in photosynthesis in which
oxygen and carbon dioxide compete for the same
binding site.
• If carbon dioxide levels are high, more carbon
dioxide binds to rubisco and photosynthesis
continues.
• If oxygen levels are high, however, then oxygen
binds to rubisco and produces carbon dioxide and
ammonia. This is wasteful since no ATP or NADPH
is formed.
Chapter 8
Cellular Energy
8.2 Photosynthesis
Alternative Pathways
 C4 plants
There is an energetic cost: +2 ATP for each CO2 fixed (but essentially NO
oxygenation) .Many of the C4 pathway enzymes are regulated by light
(active in light). C4 pathway allows more efficient carbon fixation at high
temperatures
1) PEP carboxylase binds CO2 at very low conc, so stomata can partially
close
2) photorespiration is very low, so no effect of higher [O2] at higher temps
The C4 pathway is mostly found among tropical grasses (growing in warm,
sunny environments). C4 plants cannot compete with C3 plants in moist,
colder, and less sunny environments. Less than 1% of plant species use C4
photosynthesis.
Chapter 8
Cellular Energy
8.2 Photosynthesis
Alternative Pathways
 C4 plants
C4 Carbon Fixation is a method some plants use to avoid the problems
associated with rubisco and photorespiration.
C4 plants carry out the light reactions of photosynthesis in the mesophyll like
other plants, but they carry out the light-independent reactions in the
bundle sheath cells.
The enzyme in the bundle sheath cells, PEP carboxylase, has a higher
affinity for grabbing carbon dioxide than rubisco. This gives C4 plants a
better chance of survival in tightly packed areas where carbon dioxide may
be limited even though less glucose is produced per photon of light energy.
C4 plants cannot compete with C3 plants in moist, colder, and less sunny
environments. Less than 1% of plant species use C4 photosynthesis.
Chapter 8
Cellular Energy
8.2 Photosynthesis
Alternative Pathways
 CAM plants
 Plants that close their stomata during the day to reduce water loss and
open them at night for carbon uptake.
 CAM plants cannot compete with C3 plants in a moist, cool environment,
because closing stomata during the day is much less efficient.
 Some plants are facultative CAM plants, though. They can switch between
C3 and CAM photosynthesis, depending on environmental conditions.
 Only about 3 to 4% of earth's plant species can be characterized as CAM
plants.
Water use efficiencies for C3, C4, ad
CAM plants:
• C3 = 400 to 500 g water lost / gram CO2 fixed
• C4= 250 to 300 g water lost / gram CO2 fixed.
• CAM = 50 to 100 g water lost / gram CO2 fixed.
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.
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
Anaerobic Respiration
 The anaerobic pathway that follows glycolysis
 Two main types
 Lactic acid fermentation
 Alcohol fermentation
Cellular
Respiration
Chapter 8
Cellular Energy
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Chapter Diagnostic Questions
Formative Test Questions
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Standardized Test Practice
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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.
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
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
Chapter 8
Cellular Energy
8.1 Formative
Questions
Which law of thermodynamics explains
why the ladybug receives the least amount
of usable energy?
Chapter 8
Cellular Energy
8.1 Formative
Questions
A. the first law of thermodynamics
B. the second law of thermodynamics
Chapter 8
Cellular Energy
8.1 Formative
Questions
True or False
All of the energy from the food you eat
comes from the sun.
Chapter 8
Cellular Energy
8.1 Formative
Questions
Why is cellular respiration a catabolic pathway?
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?
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?
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
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. 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?
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?
A. to make ATP
B. to process H2O
C. to store glucose
D. to deliver oxygen
Chapter 8
Cellular Energy
8.3 Formative
Questions
Which represents the general sequence of
cellular respiration?
A. TCA cycle
chemiosmosis
B. glycolysis
Krebs cycle
C. electron absorption
phosphorylation
D. aerobic pathway
fermentation
glycolysis
electron transport
catalysis
anaerobic pathway
Chapter 8
Cellular Energy
8.3 Formative
Questions
Which stage of cellular respiration is the
anaerobic process?
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?
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
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
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
Chapter 8
Cellular Energy
Standardized Test
Practice
Which metabolic process is photosynthesis?
A
B
Chapter 8
Cellular Energy
Standardized Test
Practice
At the beginning of photosynthesis, which
molecule is split to produce oxygen (O2) as
a waste product?
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
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+
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.
C. C6H12O6 is broken down into CO2.
D. NADH and FADH2 gain electrons.
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
D. an increased
demand for ATP
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
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
 Visualizing Electron Transport