Photosynthesis

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Chapter 4

• Photosynthesis

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• Photosynthesis is the process by which certain
  organisms use light energy
• To make sugar and oxygen gas from carbon dioxide
  and water
• What does it need? (Input)
• What does it make? (Output)

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Trophic Roles

• Autotrophs ? Producers of the biosphere
• produce organic molecules from CO2 inorganic
  raw materials
• Heterotrophs ? consumers

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Learning Target

• 1. Describe Oxidation Reduction reactions

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REDOX Reactions
LEO the Lion Says GER
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REDOX Reactions

• Oxidation
• When a compound loses electrons
• Reduction
• When a compound gains electrons
• CO2 H2O energy ? C6H12O6 O2
• CO2 is reduced to form glucose
• Water is oxidized to form O2

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• Photosynthesis is a redox process, as is cellular
  respiration
• In photosynthesis
• H2O is oxidized and CO2 is reduced

Figure 7.4A, B
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Learning Check

• If H2O is losing electrons than it is being
  reduced/oxidized
• Co2 is being reduced/oxidized, which means it is
  gaining/losing electrons.

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Photosynthesis Overview

• Light reactions
• Depend on light
• Occur in Thylakoid Membrane
• Light Independent (Dark) reactions
• Does NOT need light
• Occurs in the Stroma

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Learning Target

• Compare contrast the structure function of
  mitochondria chloroplast
• 15. Determine what factors affect the process of
  photosynthesis cellular respiration

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Location, location, location

• Where does the Light Dependent Reaction occur?
• The Light Independent reaction?

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Chloroplast Structure

• Found in mesophyll
• 1 mesophyll cell may have 30 chloroplasts
• Stomata regulate passage of CO2, O2 and H2O

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Learning Check

• Where does the Light Dependent Reaction occur?
• The Light Independent reaction?

• What factors could affect the process of
  photosynthesis?

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Learning Targets

• 11. Describe the purpose of Chlorophyll
  Accessory pigments.

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Pigments

• Pigments
• Absorb light energy
• Boost e- ?become unstable!
• Chlorophyll
• Chlorophyll a ? main pigment ? blue-green
• Chlorophyll b ? accessory pigment ? yellow-green
• Other accessory pigments ? absorb different
  wavelengths of light
• Carotenoids ? yellow-orange
• Xanthophyll ?yellow
• Rhodophyll ? red
• Fucoxanthin ? brown

Why are plants green?
Why are plants changing color?
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Photosystems

• Pass energy ? reaction center (chlorophyll a
  molecule) ? transfers energy to primary electron
  acceptor
• antenna pigments are primarily chlorophyll b,
  carotenoids xanthophyll

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Learning Check

• What is the purpose/function of pigments?

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Photosynthesis Overview

• Light reactions
• light energy ? chemical energy (ATP and NADPH)
  and produce O2
• Light Independent (Dark) reactions
• Using ATP and NADPH from the light reactions
  ?form sugar from CO2

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Learning Target

• 6. Explain how electron transport chains (ETC)
  establish an electrochemical gradient across
  membranes.

• 7. Contrast Chemiosmosis in Cellular Respiration
  and Photosynthesis

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ETC, Chemiosmosis ATP Synthase

• Powers ATP synthesis in light reactions
• electrons (e-) are passed along a chain of
  proteins (called the ETC) in the membrane ? H
  pumped into Thylakoid space (chemiosmosis)
• H diffuse back across the membrane through ATP
  synthase ? powers the phosphorylation of ADP to
  produce ATP (photophosphorylation)

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• Photophosphorylation http//vcell.ndsu.nodak.edu/
  animations/atpgradient/movie.htm

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Learning Check!

• ETC uses the energy of e- being passed along to
  pump _______ from the ________ into the thylakoid
  _______

• Chemiosmosis is the movement of ______ to create
  a ________concentration.

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Learning Target

• 3. Identify the inputs and outputs and location
  of the light reactions and Calvin Cycle.
• 4. Explain the role of NADH, FADH2, and NADPH.
• 14. Summarize how energy is transferred during
  photosynthesis and cellular respiration.

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Electron Carriers

• NAD
• Reacts with C-H bonds to become NADH
• NADP
• Reacts with free e- and H ions
• ADP ? ATP
• diffusion of H through ATP Synthase

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LDR

• Inputs?
• Outputs?
• Two types
• Noncyclic
  Photophosphorylation
• Cyclic Photophosphorylation
  

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Non-cyclic photophosphorylation
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• Learning Target
• 12. Describe the connection between PS2 PS1

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Light Dependent RXN animation

• http//www.science.smith.edu/departments/Biology/B
  io231/ltrxn.html
• http//vcell.ndsu.nodak.edu/animations/photosynthe
  sis/movie-flash.htm

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Cyclic Photophosphorylation

• Primitive ? used by bacteria
• Electron boosted out of P1 ? ETC ? returned to P1
• Electron drives proton pumps? chemiosmosis ? ATP

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Learning Targets

• 3. Identify the inputs and outputs and location
  of the light reactions and Calvin Cycle.
• 4. Explain the role of NADH, FADH2, and NADPH.
• 15. Summarize how energy is transferred during
  photosynthesis and cellular respiration.

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Calvin Cycle/Light Independent Reactions

• Occur in the dark or the light
• Light independent reactions
• 3 steps
• Carbon fixation
• Reduction
• Regeneration of RuBP

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Step 1Carbon Fixation

• RuBP (ribulose bisphosphate)
• 5 C sugar
• Catalyzed by Rubisco (RuBP carboxylase)
• Adds CO2
• Creates an unstable 6 C molecule that splits
• Creates PGA (3 C moleucle

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Step 2Reduction

• PGA gets phosphorylated by ATP (gets its energy)
• Reduced by NADPH (gets its e-)
• Produces G3P (PGAL)
• some G3P ? glucose
• most G3P ? regenerate RuBP

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Step 3Regeneration of RuBP

• 1 G3P moves out to eventually become glucose
• G3P ? rearranged into RuBP
• Requires input of 3 ATP
• Takes 6 turns of cycle ? 1 glucose

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http//www.science.smith.edu/departments/Biology/B
io231/calvin.html
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Alternative mechanismsPhotorespiration

• C3 plants ? rice, wheat, soybeans
• Uses Co2 directly to make PGA
• On hot, dry days they close their stomata
• no CO2 taken in and O2 builds up
• rubisco substitutes O2 for CO2
• Creates a 2 C compound
• 2 C compound gets broken down ? releases CO2
  water
• Called photorespiration
• Uses light, releases CO2 and water
• Doesnt make glucose

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Alternative mechanismsC4 Plants

• Sunny ecosystems
• C is fixed into 4 C molecule
• Carbon fixed outside cells (in bundle sheath
  cells ? very efficient ? requires extra ATP
• Only fixes C, not oxygen
• Donates the carbon to Calvin Cycle
• Balances out photorespiration saves water
• Corn and sugarcane are a C4 plants

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Alternative mechanismsCAM Plants

• Crassulacean acid metabolism ? Hot/dry climates
• Orchids, cacti, pineapple etc.
• Stomates open at night to reduce water loss ?
  evaporation
• CO2 is fixed into a 4 C compound, used later

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