9'2 Photosynthesis

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9.2 Photosynthesis

• Trapping light energy (sun) and converting it to
  chemical energy (carbohydrate which one?)
• Happens where?

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Photosynthesis

• Using light from the sun, plants combine water
  and carbon dioxide to make sugar .

• General Equation
• 6CO2 6H2O energy ? C6H12O6 6O2
• Reactants Products

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WHAT EXACTLY IS LIGHT?

• Light visible spectrum
• E travels in packets called photons
• These photons travel in waves
• The amount of energy in each packet depends on
  the wavelength (?)

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The electromagnetic spectrum
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WHAT EXACTLY IS LIGHT?
?
?

• Short ? ____ E _____ frequency
• Long ? _____ E ____ frequency
• ?s range (for visible light) 400-700nm
• (violet-red)
• Molecules can either _______ the entire photon or
  not (______)

?
?
absorb
reflect
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Figure 10.7 Determining an absorption spectrum
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Why leaves are green interaction of light with
chloroplasts
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How do plants capture light?

• Plants have 2 light-capturing pigments
• 1. Chloroplasts
• Absorb red, blue
• Reflect 500-600nm (green)
• 2. Carotenoids
• Absorb light blue, green
• Reflect yellow, orange, red

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The structure of the chloroplasts

• Each is surrounded by a double-membrane envelope
• Thylakoid
• Stroma
• Grana
• The pigment is chlorophyll
• Comes in 2 forms
• Chlorophyll A and Chlorophyll B

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Photosynthesis

• Sets of Reactions (steps)
• 1. Light Reactions
• Light dependent
• 2. Calvin Cycle (Melvin Calvin)
• Light independent
• dark reactions

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1. Light Reactions

• Occurs in the grana/thylakoids chlorophyll
• Light E ? Chemical E (glucose)

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1. Light Reactions

• 1. Light absorbs into 2 reaction centers
• 680nm 700nm
• (photosystem II) (photosystem I)
• 2. Electrons are energized excited by light

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Excitation of chlorophyll by light
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1. Light Reactions

• 1. Light absorbs into 2 reaction centers
• 680nm 700nm
• (photosystem II) (photosystem I)
• 2. Electrons are energized excited
• 3. P680 energy splits H2O Releases H O
• 4. Excited e-s convert ADP to ATP
• 5. P700 e-s convert NADP to NADPH
• NADP is a carrier molecule (used in dark
  reactions)

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Photosystems

• Light harvesting units of the thylakoid membrane
• Composed mainly of protein and pigment antenna
  complexes
• Antenna pigment molecules are struck by photons
• Energy is passed to reaction centers
• e-s are excited and passed through an electron
  transport system
• A series of proteins in the thylakoid membrane

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Electron Transport

• photons excite chlorophyll e-
• e-s travel to Photosystem I down an electron
  transport chain
• as e-s fall, ADP forms ATP

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1. Light Reactions

• Light Reactions Summary
• Light energy is converted to chemical energy to
  split hydrogen from water.
• Takes place in the grana of the chloroplasts (the
  coin-like stacks of thylakoids).
• Byproducts are
• Oxygen waste
• NADPH/ATP used in the dark reactions

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Part 2 of PhotosynthesisLight Independent
(dark) reactions
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2. Light Independent Reactions

• Calvin Cycle
• ATP and NADPH from the light reactions are used
  along with CO2 to form a simple sugar (glucose).
• Takes place in the stroma of the chloroplasts
  (the liquid filling).
• Byproducts are
• C6H12O6 (glucose)
• ADP and NADP (which return to the light
  reactions).

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The Calvin cycle

• 3 molecules of CO2 are fixed into
  glyceraldehyde 3-phosphate (G3P)
• Phases 1- Carbon fixation each CO2 is
  attached to RuBP (rubisco enzyme) 2-
  Reduction electrons from NADPH reduces to G3P
  ATP used up
• 3- Regeneration G3P rearranged to
  RuBP ATP used cycle continues

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Calvin Cycle, net synthesis

• For each G3P (and for 3 CO2). Consumption of
  9 ATPs 6 NADPH (light reactions regenerate
  these molecules)
• G3P can then be used by the plant to make glucose
  and other organic compounds
• GLUCOSE!

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Figure 10.17 The Calvin cycle (Layer 3)
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Sunlight
O2
Photosystem I II
H2O
ATP
NADP ADP
NADPH
CO2
Calvin cycle
Glucose
CHLOROPLAST
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Photosynthesis an overview

• H2O is split, e- (along w/ H) are transferred to
  CO2, reducing it to sugar
• 2 major steps
  
• light reactions (photo)
• NADP (electron acceptor) to NADPH
• Photophosphorylation ADP ---gt ATP
• Calvin cycle (synthesis)
• Carbon fixation carbon into sugars

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Tracking atoms through photosynthesis
Released Oxygen came from Water!!!!