Life: the Science of Biology, Purves 6th ed.

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Life the Science of Biology, Purves 6th ed.
CHAPTER 8Photosynthesis Energy from the Sun
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Chapter 8 Photosynthesis Energy from the Sun

• Photosynthesis
• Identifying Photosynthetic Reactants and Products
• The Two Pathways of Photosynthesis An Overview
• Properties of Light and Pigments

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Chapter 8 Photosynthesis Energy from the Sun

• Light Reactions Light Absorption
• Making Sugar from CO2 The CalvinBenson Cycle
• Metabolic Pathways in Plants

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Photosynthesis

• Life on Earth depends on the absorption of light
  energy from the sun.

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Photosynthesis

• In plants, photosynthesis takes place in
  chloroplasts.

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Identifying Photosynthetic Reactants and Products

• Photosynthesizing plants take in CO2, water, and
  light energy, producing O2 and carbohydrate. The
  overall reaction is
• 6 CO2 12 H2O light ? C6H12O6 6 O2 6 H2O
• The oxygen atoms in O2 come from water, not from
  CO2. Review Figures 8.1, 8.2

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Figure 8.1
figure 08-01.jpg

• Figure 8.1

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Figure 8.2
figure 08-02.jpg

• Figure 8.2

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The Two Pathways of Photosynthesis An Overview

• In the light reactions of photosynthesis,
  electron flow and photophosphorylation produce
  ATP and reduce NADP to NADPH H. Review Figure
  8.3

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Figure 8.3
figure 08-03.jpg

• Figure 8.3

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The Two Pathways of Photosynthesis An Overview

• ATP and NADPH H are needed for the reactions
  that fix and reduce CO2 in the CalvinBenson
  cycle, forming sugars. Review Figure 8.3

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Properties of Light and Pigments

• Light energy comes in packets called photons, but
  it also has wavelike properties. Review Figure 8.4

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Figure 8.4
figure 08-04.jpg

• Figure 8.4

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Properties of Light and Pigments

• Pigments absorb light in the visible spectrum.
  Review Figure 8.5

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Figure 8.5
figure 08-05.jpg

• Figure 8.5

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Properties of Light and Pigments

• Absorption of a photon puts a pigment molecule in
  an excited state with more energy than its ground
  state. Review Figure 8.6

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Figure 8.6
figure 08-06.jpg

• Figure 8.6

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Properties of Light and Pigments

• Each compound has a characteristic absorption
  spectrum which reveals the biological
  effectiveness of different wavelengths of light.
  Review Figures 8.7, 8.8

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Figure 8.7
figure 08-07.jpg

• Figure 8.7

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Figure 8.8
figure 08-08.jpg

• Figure 8.8

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Properties of Light and Pigments

• Chlorophylls and accessory pigments form antenna
  systems for absorption of light energy. Review
  Figures 8.7, 8.9, 8.11

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Figure 8.9
figure 08-09.jpg

• Figure 8.9

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Figure 8.11
figure 08-11.jpg

• Figure 8.11

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Light Reactions Light Absorption

• An excited pigment molecule may lose its energy
  by fluorescence, or by transferring it to another
  pigment molecule. Review Figures 8.10, 8.11

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Figure 8.10
figure 08-10.jpg

• Figure 8.10

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Electron Flow, Photophos-phorylation, and
Reductions

• Noncyclic electron flow uses two photosystems
  Photosystem II uses P680 chlorophyll, from which
  light-excited electrons pass to a redox chain
  that drives chemiosmotic ATP production.
  Light-driven water oxidation releases O2, passing
  electrons to P680 chlorophyll. Photosystem I
  passes electrons from P700 chlorophyll to another
  redox chain and then to NADP, forming NADPH
  H. Review Figure 8.12

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Figure 8.12 Part 1
figure 08-12a.jpg

• Figure 8.12 Part 1

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Figure 8.12 Part 2
figure 08-12b.jpg

• Figure 8.12 Part 2

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Electron Flow, Photophos-phorylation, and
Reductions

• Cyclic electron flow uses P700 chlorophyll
  producing only ATP. Its operation maintains the
  proper balance of ATP and NADPH H in the
  chloroplast. Review Figure 8.13

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Figure 8.13
figure 08-13.jpg

• Figure 8.13

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Electron Flow, Photophos-phorylation, and
Reductions

• Chemiosmosis is the source of ATP in
  photophosphorylation. Electron transport pumps
  protons from stroma into thylakoids, establishing
  a proton-motive force. Proton diffusion to stroma
  via ATP synthase channels drives ATP formation
  from ADP and Pi. Review Figure 8.14

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Figure 8.14
figure 08-14.jpg

• Figure 8.14

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Electron Flow, Photophos-phorylation, and
Reductions

• Photosynthesis probably originated in anaerobic
  bacteria that used H2S as a source of electrons
  instead of H2O. Oxygen production by bacteria was
  important in eukaryote evolution.

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Making Sugar from CO2 The CalvinBenson Cycle

• The CalvinBenson cycle makes sugar from CO2.
  This pathway was elucidated through use of
  radioactive tracers. Review Figure 8.15

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Figure 8.15
figure 08-15.jpg

• Figure 8.15

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Making Sugar from CO2 The CalvinBenson Cycle

• The CalvinBenson cycle has three phases
  fixation of CO2, reduction and carbohydrate
  production, and regeneration of RuBP. RuBP is the
  initial CO2 acceptor, 3PG is the first stable
  product of CO2 fixation. Rubisco catalyzes the
  reaction of CO2 and RuBP to form 3PG. Review
  Figures 8.16, 8.17

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Figure 8.16
figure 08-16.jpg

• Figure 8.16

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Figure 8.17
figure 08-17.jpg

• Figure 8.17

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Metabolic Pathways in Plants

• Plants respire in light and darkness, but
  photosynthesize only in light. A plant must
  photosynthesize more than it respires, giving it
  a net gain of reduced energy-rich compounds.

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Metabolic Pathways in Plants

• Photosynthesis and respiration are linked through
  the CalvinBenson cycle, the citric acid cycle,
  and glycolysis. Review Figure 8.22

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Figure 8.22 Part 1
figure 08-22a.jpg

• Figure 8.22 Part 1

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Figure 8.22 Part 2
figure 08-22b.jpg

• Figure 8.22 Part 2