Photosynthesis

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Chapter 10

• Photosynthesis

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Figure 10.1 Photoautotrophs
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REDOX in Respiration

• Redox involves loss or gain of a hydrogen atom or
  an electron
• C6H12O6 6O2 ---gt 6CO2 6H2O
• Energy given off as ATP
• Carbon loses hydrogen therefore is oxidized.
• Oxygen gains hydrogen therefore is reduced.

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REDOX in Photosynthesis

• Redox involves loss or gain of a hydrogen atom or
  an electron
• 6CO2 6H2O ---gt C6H12O6 6O2
• Energy supplied by light
• Carbon gains hydrogen therefore is reduced.
• Oxygen loses hydrogen therefore is oxidized.

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Figure 10.3 Focusing in on the location of
photosynthesis in a plant
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Two parts to photosynthesis
Melvin Calvin

• Light-dependent reactions (light) LDRs
• Light-independent reactions (dark) LIRs

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Figure 10.5 An overview of photosynthesis
cooperation of the light reactions and the Calvin
cycle (Layer 1)
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Figure 10.5 An overview of photosynthesis
cooperation of the light reactions and the Calvin
cycle (Layer 2)

• ATP
• Nicotinamide Adenine Dinucleotide Phosphate
  (NADPH)
• NADP H 2e- -------gt NADPH
• Oxidized form Reduced form

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Figure 10.5 An overview of photosynthesis
cooperation of the light reactions and the Calvin
cycle (Layer 3)
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Factors limiting photosynthesis

• 1. Light intensity (LDRs)
• 2. Substrates (LIRs)
• Low CO2 affects rate directly
• Low water affects rate indirectly by closing
  stomata
• 3. Temperature (LIRs)
• 4. Photorespiration (LIRs)

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Figure 10.6 The electromagnetic spectrum
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Figure 10.7 Determining an absorption spectrum
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Figure 10.9 Evidence that chloroplast pigments
participate in photosynthesis absorption and
action spectra for photosynthesis in an alga
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Figure 10.10 Location and structure of
chlorophyll molecules in plants
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Accessory Pigments

• Carotene
• Found in

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Figure 10.11 Excitation of isolated chlorophyll
by light
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Chlorophyll molecules work in Photosystems
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Photosystem 1

• 96 Chlorophyll molecules
• 22 Carotinoids
• 4 Lipids
• 2 Phytoquinones
• 3 Iron Sulphate clusters
• Lots of proteins

PSII p680 PSI p700
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Photosystem 1
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• Photosystem Reaction Center
• PRC chlorophyll donates electrons to acceptor
• Oxidized photosystem then grabs electrons
  (oxidizes) from electron donor (water)

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High Energy Shuttles

• ATP
• Nicotinamide Adenine Dinucleotide Phosphate
  (NADPH)
• NADP H 2e- -------gt NADPH
• Oxidized form Reduced form

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Two types of photosynthesis

• Non-cyclic photophosphorylation
• Z-scheme
• Plants
• Makes ATP and NADPH
• Cyclic photophosphorylation
• Plants and bacteria
• Makes ATP

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Figure 10.13 How noncyclic electron flow during
the light reactions generates ATP and NADPH
(Layer 1)
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Figure 10.13 How noncyclic electron flow during
the light reactions generates ATP and NADPH
(Layer 2)
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Figure 10.13 How noncyclic electron flow during
the light reactions generates ATP and NADPH
(Layer 3)
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Figure 10.13 How noncyclic electron flow during
the light reactions generates ATP and NADPH
(Layer 4)
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Figure 10.12 How noncyclic electron flow during
the light reactions generates ATP and NADPH
(Layer 5)
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P680
P700
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Figure 10.15 Cyclic electron flow Cyclic
photophosphorylation
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Figure 10.16 Comparison of chemiosmosis in
mitochondria and chloroplasts
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Figure 10.17 The light reactions and
chemiosmosis the organization of the thylakoid
membrane
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Now What?

• ATP and NADPH made during light-dependent
  reactions
• These high-energy shuttles used in the
  light-independent reactions to make glucose

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C3
First step in carbon fixation
Ribulose Bisphosphate Carboxylase/ Oxygenase
(RUBISCO)
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Figure 10.17 The Calvin cycle (Layer 1)
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Figure 10.18 The Calvin cycle (Layer 2)
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Figure 10.18 The Calvin cycle (Layer 3)
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Photorespiration Ribulose Bisphosphate
Carboxylase/ Oxygenase (RUBISCO)

• Problem High O2 oxidizes RuBP to produce CO2
  with no ATP or NADPH synthesis. At 25oC, PR
  oxidizes 20 of fixed carbon. WASTE
• Problem This Photorespiration speeds up at high
  temperatures. Carbon fixation does not increase.
  BIG WASTE
• Solution C4 Photosynthesis (C4 and CAM plants)

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C4 and Crassulacean Acid Metabolism

• C4
• Separates RUBISCO from high levels of oxygen
  physically
• CAM
• Separates RUBISCO from high levels of oxygen
  temporally

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Figure 10.19 C4 leaf anatomy and the C4 pathway
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Figure 10.19 C4 and CAM photosynthesis compared
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Figure 10.20 A review of photosynthesis
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Figure 9.1 Energy flow and chemical recycling in
ecosystems