Spectrophotometer

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Spectrophotometer

• Instrument used to measure what wavelengths of
  light are being absorbed by pigments
• Directs beams of light through a solution of
  pigment and measures the fraction of light
  transmitted at each wavelength

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Figure 10.7 Determining an absorption spectrum
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What happens when pigments absorb photons.

• When a molecule absorbs a photon, one of the
  molecules electrons is elevated to an orbital
  where it has more potential energy
• Normal level ground state
• Higher energy level excited state
• see pages 184-185

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Figure 10.12 How noncyclic electron flow during
the light reactions generates ATP and NADPH
(Layer 1)
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Figure 10.12 How noncyclic electron flow during
the light reactions generates ATP and NADPH
(Layer 2)
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Figure 10.12 How noncyclic electron flow during
the light reactions generates ATP and NADPH
(Layer 3)
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Figure 10.12 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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Photophosphorylation

• Method of generating ATP by using light to add P
  to ADP
• Occurs in Light Reactions

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Cyclic vs. Noncyclic electron flow

• Noncyclic pg 186
• uses Photosystem II, an ETC (with the electron
  carrier plastoquinone, Pq) , Photosystem I, and
  another ETC using an iron-containing protein
  called ferredoxin
• Cyclic pg. 187
• uses only Photosystem I and the second ETC no
  production of NADPH and no release of Oxygen, but
  DOES produce ATP to be used to make up the
  difference needed due to Calvin cycle demands..

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Figure 10.14 Cyclic electron flow
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Chemiosmosis is similar in Chloroplasts and
Mitochondria

• In both, ETC pumps protons across a membrane from
  areas of low concentration to high concentration
  
• When these protons diffuse back across the
  membrane through ATP synthase, they drive the
  synthesis of ATP
• See page 188

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Figure 10.16 The light reactions and
chemiosmosis the organization of the thylakoid
membrane
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Figure 10.15 Comparison of chemiosmosis in
mitochondria and chloroplasts
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Calvin Cycle

• Three phases
• 1. Carbon fixation CO2 it attached to RuBP
  catalyzed by the enzyme rubisco (most plants
  are called C3 plants because first intermediate
  is 3-phosphoglycerate)
• 2. Reduction
• 3. Regeneration of RuBP

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Figure 10.17 The Calvin cycle (Layer 3)
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Alternatives mechanisms of carbon fixation

• Photorespiration occurs when O2 levels overtake
  CO2 levels rubisco adds O2 to the Calvin cycle
  instead of CO2, the product splits, and the 2-C
  carbon gets exported from the chloroplast
  mitochondria and peroxisomes break this down into
  CO2
• MAKES NO ATP AND GENERATES NO FOOD!!!
• photorespiration decreases photosynthetic output
  by diverting organic material from the Calvin
  cycle

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• C4 pathways preface the Calvin cycle with an
  alternate mode of carbon fixation and four carbon
  compound is first product (sugarcane and corn)
• Uses different CELLS to do carbon fixation and
  the Calvin cycle spatial separation see page
  193
• CO2 PEP make oxaloacetate

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• CAM plants adaptation to arid conditions found
  in succulents
• Carbon fixation occurs in same cells, but at
  different times temporal separationof processes
• Open stomata during night and close them during
  day
• Make organic acids at night and store them in
  vacuoles until morning when stomata close and
  light reactions can supply ATP and Calvin cycle
  (then, release CO2 from acids)
• Crassulacean acid metabolism

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Figure 10.19 C4 and CAM photosynthesis compared
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Figure 10.20 A review of photosynthesis