Biology, Seventh Edition
Solomon • Berg • Martin
Chapter 8
Photosynthesis:
Capturing Energy
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 8 Photosynthesis: Capturing Energy
• Light
• Composed of photons
• Visible light small portion of
electromagnetic spectrum
• All energy travels as waves
• Shorter wavelengths have more
energy than longer wavelengths
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 8 Photosynthesis: Capturing Energy
Electromagnetic
spectrum
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Biology, Seventh Edition
CHAPTER 8 Photosynthesis: Capturing Energy
• Chloroplasts
• Organelles enclosed by a double
membrane
• Site of photosynthesis
• Located mainly within mesophyll cells
inside leaf
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 8 Photosynthesis: Capturing Energy
Site of photosynthesis
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 8 Photosynthesis: Capturing Energy
• Chlorophyll
• Main photosynthetic pigment
• Chlorophyll a, chlorophyll b,
carotenoids, and other photosynthetic
pigments are components of thylakoid
membranes of chloroplasts
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 8 Photosynthesis: Capturing Energy
• Photosynthesis is redox
process
• Light energy captured and converted
to carbohydrates
• Hydrogens from water reduce carbon
• Oxygen derived from water becomes
oxidized
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 8 Photosynthesis: Capturing Energy
• Two phases of photosynthesis
• Light-dependent
–In thylakoids
–Electrons energized by light generate
ATP and NADPH
• Carbon fixation
–In stroma
–Compounds generated in phase one
provide energy for formation of
carbohydrate
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 8 Photosynthesis: Capturing Energy
Overview of photosynthesis
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Biology, Seventh Edition
CHAPTER 8 Photosynthesis: Capturing Energy
• Photosystems I and II
• Two types of photosynthetic units
involved in photosynthesis
• Each photosystem includes
–Chlorophyll molecules
–Multiple antenna complexes
• Photosystem I reaction center
–P700 has absorption peak at 700 nm
• Photosystem II reaction center
–P680 has absorption peak at 680 nm
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 8 Photosynthesis: Capturing Energy
Photosystem
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 8 Photosynthesis: Capturing Energy
• Noncyclic electron transport
• ATP and NADPH formed
• Electrons energized by absorption of
light and pass through electron
transport chain to NADP+
• Series of redox reactions
• Electrons given up by P680 are
replaced by electrons from photolysis
of H2O
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 8 Photosynthesis: Capturing Energy
Noncyclic electron transport
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 8 Photosynthesis: Capturing Energy
• Cyclic electron transport
• Electrons from photosystem I
returned to photosystem I
• ATP produced by chemiosmosis
• No NADPH or O2 generated
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 8 Photosynthesis: Capturing Energy
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 8 Photosynthesis: Capturing Energy
• ATP synthesis and electron
transport
• Electrons move down electron
transport chain
• Protons (H+) move from stroma to
thylakoid lumen, creating proton
gradient
• Greater concentration of H+ lowers
the pH
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 8 Photosynthesis: Capturing Energy
Accumulation of protons in thylakoid lumen
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Biology, Seventh Edition
CHAPTER 8 Photosynthesis: Capturing Energy
Electron transport and chemiosmosis
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 8 Photosynthesis: Capturing Energy
• Carbon fixation
• Energy of ATP and NADPH used in
formation of organic molecules from
CO2
12 NADPH + 18 ATP + 6 CO2 →
C6H12O6 + 12 NADP + + 18 ADP + 18 Pi + 6 H2O
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 8 Photosynthesis: Capturing Energy
• Three phases of Calvin cycle
• CO2 uptake
• Carbon reduction
• RuBP regeneration
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Biology, Seventh Edition
CHAPTER 8 Photosynthesis: Capturing Energy
Calvin cycle
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Biology, Seventh Edition
CHAPTER 8 Photosynthesis: Capturing Energy
Summary of photosynthesis
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Biology, Seventh Edition
CHAPTER 8 Photosynthesis: Capturing Energy
C3 and C4 plant structure compared
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Biology, Seventh Edition
CHAPTER 8 Photosynthesis: Capturing Energy
Summary
of the C4
pathway
Copyright © 2005 Brooks/Cole — Thomson Learning