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Chapter 6
Section 1 The Light Reactions
Objectives
• Explain why almost all organisms depend on
photosynthesis.
• Describe the role of chlorophylls and other pigments
in photosynthesis.
• Summarize the main events of the light reactions.
• Explain how ATP is made during the light reactions.
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Chapter 6
Section 1 The Light Reactions
Obtaining Energy, continued
• Autotrophs use energy from sunlight or from
chemical bonds in inorganic substances to make
organic compounds.
• Animals and other organisms that must get energy
from food instead of directly from sunlight or
inorganic substances are called heterotrophs.
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Chapter 6
Section 1 The Light Reactions
Overview of Photosynthesis, continued
• Equation of Photosynthesis:
6CO2 + 6H2O light energy C6H12O6 + 6O2
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Fig. 10-3
Leaf cross section
Vein
Mesophyll
Stomata
Chloroplast
CO2
O2
Mesophyll cell
Outer
membrane
Thylakoid
Stroma
Granum
Thylakoid
space
Intermembrane
space
5 µm
Inner
membrane
1 µm
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Fig. 10-6
10–5 nm 10–3 nm
103 nm
1 nm
Gamma
X-rays
rays
UV
106 nm
Infrared
1m
(109 nm)
Microwaves
103 m
Radio
waves
Visible light
380
450
500
550
600
650
700
750 nm
Longer wavelength
Lower energy
Shorter wavelength
Higher energy
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Chapter 6
Section 1 The Light Reactions
Spectrum of Light and Plant Pigments
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Fig. 10-5-4
CO2
H2O
Light
NADP+
ADP
+ P
i
Calvin
Cycle
Light
Reactions
ATP
NADPH
Chloroplast
O2
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[CH2O]
(sugar)
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Fig. 10-13-5
4
Primary
acceptor
2
H+
+
1/ O
2
2
H2O
e–
2
Primary
acceptor
e–
Pq
Cytochrome
complex
7
Fd
e–
e–
8
NADP+
reductase
3
NADPH
Pc
e–
e–
P700
5
P680
Light
1 Light
6
ATP
Pigment
molecules
Photosystem II
(PS II)
NADP+
+ H+
Photosystem I
(PS I)
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Fig. 10-14
e–
ATP
e–
e–
NADPH
e–
e–
e–
Mill
makes
ATP
e–
Photosystem II
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Photosystem I
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Fig. 10-16
Mitochondrion
Chloroplast
MITOCHONDRION
STRUCTURE
CHLOROPLAST
STRUCTURE
H+
Intermembrane
space
Inner
membrane
Diffusion
Electron
transport
chain
Thylakoid
space
Thylakoid
membrane
ATP
synthase
Stroma
Matrix
Key
ADP + P i
[H+]
Higher
Lower [H+]
H+
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ATP
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Fig. 10-18-3
Input 3
(Entering one
at a time)
CO2
Phase 1: Carbon fixation
Rubisco
3 P
Short-lived
intermediate
P
6
P
3-Phosphoglycerate
3P
P
Ribulose bisphosphate
(RuBP)
6
ATP
6 ADP
3 ADP
3
Calvin
Cycle
6 P
P
1,3-Bisphosphoglycerate
ATP
6 NADPH
Phase 3:
Regeneration of
the CO2 acceptor
(RuBP)
6 NADP+
6 Pi
P
5
G3P
6
P
Glyceraldehyde-3-phosphate
(G3P)
1
Output
P
G3P
(a sugar)
Chapter
Glucose and
other organic
menu
compounds
Phase 2:
Reduction
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Fig. 10-20
Sugarcane
Pineapple
C4
CAM
CO2
Mesophyll
cell
Organic acid
Bundlesheath
cell
CO2
1 CO2 incorporated
into four-carbon Organic acid
organic acids
(carbon fixation)
CO2
Calvin
Cycle
CO2
2 Organic acids
release CO2 to
Calvin cycle
Sugar
(a) Spatial separation of steps
Night
Day
Calvin
Cycle
Sugar
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Temporal separation
of steps
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Chapter 6
Section 2 The Calvin Cycle
Objectives
• Summarize the main events of the Calvin cycle.
• Describe what happens to the compounds that are
made in the Calvin cycle.
• Distinguish between C3, C4, and CAM plants.
• Summarize how the light reactions and the Calvin
cycle work together to create the continuous cycle of
photosynthesis.
• Explain how environmental factors influence
photosynthesis.
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Chapter 6
Section 2 The Calvin Cycle
Environmental Influences on Photosynthesis
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Chapter 6
Standardized Test Prep
Multiple Choice
1. Which of the following is a reactant in the Calvin
cycle?
A. O2
B. CO2
C. H2O
D. C6H12O6
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Chapter 6
Standardized Test Prep
Multiple Choice, continued
1. Which of the following is a reactant in the Calvin
cycle?
A. O2
B. CO2
C. H2O
D. C6H12O6
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Chapter 6
Standardized Test Prep
Multiple Choice, continued
2. Which of the following statements is correct?
F. Accessory pigments are not involved in
photosynthesis.
G. Accessory pigments add color to plants but do not
absorb light energy.
H. Accessory pigments absorb colors of light that
chlorophyll a cannot absorb.
J. Accessory pigments receive electrons from the
electron transport chain of photosystem I.
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Chapter 6
Standardized Test Prep
Multiple Choice, continued
2. Which of the following statements is correct?
F. Accessory pigments are not involved in
photosynthesis.
G. Accessory pigments add color to plants but do not
absorb light energy.
H. Accessory pigments absorb colors of light that
chlorophyll a cannot absorb.
J. Accessory pigments receive electrons from the
electron transport chain of photosystem I.
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Chapter 6
Standardized Test Prep
Multiple Choice, continued
3. Oxygen is produced at what point during
photosynthesis?
A. when CO2 is fixed
B. when water is split
C. when ATP is converted into ADP
D. when 3-PGA is converted into G3P
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Chapter 6
Standardized Test Prep
Multiple Choice, continued
3. Oxygen is produced at what point during
photosynthesis?
A. when CO2 is fixed
B. when water is split
C. when ATP is converted into ADP
D. when 3-PGA is converted into G3P
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Chapter 6
Standardized Test Prep
Multiple Choice, continued
The diagram below shows
a portion of a chloroplast.
Use the diagram to answer
the question that follows.
4. Which of the following
correctly identifies the
structure marked X and the
activities that take place
there?
F. stroma—Calvin cycle
G. stroma—light reactions
H. thylakoid—Calvin cycle
J. thylakoid—light reactions
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Chapter 6
Standardized Test Prep
Multiple Choice, continued
The diagram below shows
a portion of a chloroplast.
Use the diagram to answer
the question that follows.
4. Which of the following
correctly identifies the
structure marked X and the
activities that take place
there?
F. stroma—Calvin cycle
G. stroma—light reactions
H. thylakoid—Calvin cycle
J. thylakoid—light reactions
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Chapter 6
Standardized Test Prep
Multiple Choice, continued
5. light reactions : ATP :: Calvin cycle :
A. H+
B. O2
C. G3P
D. H2O
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Chapter 6
Standardized Test Prep
Multiple Choice, continued
5. light reactions : ATP :: Calvin cycle :
A. H+
B. O2
C. G3P
D. H2O
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Chapter 6
Standardized Test Prep
Multiple Choice, continued
The diagram below shows a
step in the process of
chemiosmosis. Use the
diagram to answer the question
that follows.
6. What is the substance
identified as Y in the
image?
F. H+
G. NAD+
H. NADPH
J. ADP synthase
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Chapter 6
Standardized Test Prep
Multiple Choice, continued
The diagram below shows a
step in the process of
chemiosmosis. Use the
diagram to answer the question
that follows.
6. What is the substance
identified as Y in the
image?
F. H+
G. NAD+
H. NADPH
J. ADP synthase
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Chapter 6
Standardized Test Prep
Short Response
Chloroplasts are organelles with areas that conduct
different specialized activities.
Where in the chloroplast do the light reactions and
the Calvin cycle occur?
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Chapter 6
Standardized Test Prep
Short Response, continued
Chloroplasts are organelles with areas that conduct
different specialized activities.
Where in the chloroplast do the light reactions and
the Calvin cycle occur?
Answer:
The light reactions of photosynthesis occur along the
thylakoid membrane. The Calvin cycle occurs in the
stroma, surrounding the thylakoids.
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Chapter 6
Standardized Test Prep
Extended Response
The reactions of photosynthesis make up a
biochemical pathway.
Part A What are the reactants and products for both
the light reactions and the Calvin cycle?
Part B Explain how the biochemical pathway of
photosynthesis recycles many of its own
reactants, and identify the recycled reactants.
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Chapter 6
Standardized Test Prep
Extended Response, continued
Answer:
Part A The reactants for the light reactions of
photosynthesis are sunlight, water, NADP+, and ADP.
The products are oxygen, ATP, and NADPH. The
reactants for the Calvin cycle are ATP, NADPH, CO2,
and RuBP. The products are NADP+, ADP, and
organic compounds.
Part B ADP/ATP, NADP+/NADPH, and electrons are
recycled during photosynthesis. RuBP, which reacts
with CO2 in the Calvin cycle, is regenerated at each
turn of the cycle.
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