Ch. 10 PHOTOSYNTHESIS

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Ch. 10 PHOTOSYNTHESIS
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History

• Jan Van Helmont
• Mass of plant, container and soil, document mass
  of water new growth was greater
• Joseph Priestley
• Mint plant keeps candle lit inside jar, plants
  produce oxygen
• Also discovered/named oxygen
• Jan Ingenhousz
• Plants only produce oxygen if in the light
• Melvin Calvin
• Steps of dark reactions using radioactive tracers
• CARBON DIOXIDE COMING INTO PLANT CREATING
  CARBOHYDRATES .. BIOMASS

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Energy Flow

• Energy flow is one directional
• From sun (solar energy) to chemical then
  mechanical energy.. Eventually heat
• Elements/ nutrients/ matter cycles
• C cycle, N cycle, Water cycle, etc.
• Food webs
• Autotrophs self feeding photoautotrophic and
  chemoautotrophic
• Heterotrophs other feeding herbivores,
  carnivores, omnivores, detritivores, decomposers,
  parasites, etc.

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Leaf Structure

• Chlorophyll is a chemical/ pigment
• Chloroplasts are structures that contain
  chlorophyll
• Many layers (Membranes)
• Other plastids
• chromoplast
• leukoplast
• amyloplasts
• Specialized cells/ tissues

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From chloroplast to leaf
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Light Reactions

• Require light to occur
• Require water
• Light energy is used to split a water molecule
• Thylakoid is site of reaction
• Provides H for NADPH, e- and
• Generates oxygen that is released

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Light Reaction Details

• Photons (units of light), at l just below 500
  reach chloroplast and strike chlorophyll on
  thylakoid membrane
• e- on chlorophyll are excited
• e- are passed to primary acceptor
• Heat is given off
• Water is split
• Oxygen helps oxidize reaction, O loses H and e-
  returns to chlorophyll
• NADPH and ATP are generated

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Noncyclic electron flow
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Cyclic electron flow
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Dark Reactions

• Occurs in stroma of chloroplast
• Does not require dark ( or light )
• Needs NADPH and ATP from light reactions
• Uses CO2
• Generates glycerol 3 phosphate (1/2 of a
  glucose. aka PGAl )

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Details of Calvin cycle

• Phase 1 CO2 is incorporated, called carbon
  fixation
• Phase 2 phosphorylation, ATP spent, e- from
  NADPH reduce the C chain so it stores more
  potential energy
• 6 molecules with 3 C are made 5 are recycled
  and one is released as a future glucose
• Phase 3 cycles

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Summary

• Rubisco is the enzyme that catalyzes the first
  step of Calvin cycle since in all chloroplasts
  of all cells of all leaves, its the most
  abundant protein on Earth.
• sunlight
• 6CO2 6H2O C6H12O6 6O2
• chlorophyll

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Compare and contrast

• PHOTOSYNTHESIS
• Chloroplast
• stroma and inner membrane
• ETC and cycle
• ETC first
• CO2 in, O2 out
• Fixes C into chains
• Stores energy

• RESPIRATION
• Mitochondria
• matrix and inner membrane
• ETC and cycle
• ETC last
• C cpd in, CO2 out
• Breaks C bonds
• Releases energy

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Alternatives

• C3 plants ( rice and wheat grasses)
• Close stomata, hot dry weather, less sugar do
  photorespiration
• Photorespiration process adds O2 by rubisco and
  this product then splits releasing CO2
• C4 plants
• Sugar cane and corn
• Make 4 C cpd first then Calvin making PEP that
  can fix CO2 easily, even when hot.
• CAM
• Succulent plants like cactus and pineapples
• Crassulacean Acid Metabolism make and store
  organic acids to be broken down to CO2 and used
  over night when cooler