Photosynthesis

1
Photosynthesis

• The Flow of Energy

2
Autotrophs vs. Heterotrophs

• Autotrophs self-feeders, an organism that
  makes all its own organic matter from inorganic
  nutrients (are producers)
• Heterotrophs other-feeders, must feed on
  other organisms to obtain organic matter (are
  consumers)

3
Photosynthesis

• Jan van Helmont, Joseph Priestley, and Jan
  Ingenhousz did experiments that revealed that in
  the presence of light, plants transform water and
  carbon dioxide into carbohydrates and release
  oxygen
• 6CO2 6H2O ? C6H12O6 6O2

4
Light

• Visible spectrum ROYGBIV
• Red longest wavelength
• Violet shortest
• wavelength
• Color of an object
• is determined by
• the color the object reflects

5
Chloroplasts and Pigments

• Chloroplast organelle
• where photosynthesis occurs
• Chlorophyll (a and b) a green pigment, most
  important in photosynthesis
• Carotenoids yellow, orange and red pigments
  also found in chloroplasts
• Absorbed light is transformed from light energy
  to chemical energy

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Leaves

• Most photosynthesis occurs in the leaves
• Chloroplasts are found in the mesophyll
• CO2 enters the leaf and O2 exits the leaf through
  stomata

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Leaves
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Inside a Chloroplast

• Thylakoids saclike photosynthetic membranes
  (chlorophyll)
• Grana stacks of thylakoids
• Stroma the fluid surrounding the thylakoids

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Overview of Photosynthesis

• Endergonic reaction a chemical reaction that
  uses or stores energy
• Two steps of photosynthesis
• Light Reactions
• Calvin Cycle

10
Light Reactions

• Require light
• Use energy from light to produce ATP and NADPH
  (an electron carrier)
• Occurs in the grana
• Energy from excited electrons is used to bond
  ADP and Pi to form ATP
• Inputs H2O, light
• Outputs O2, ATP, NADPH

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Photosystems

• Cluster of pigment molecules
• Photon strikes a pigment molecule, the energy
  jumps from pigment to pigment
• Reaction center a special chlorophyll a
  molecule
• Primary Electron Acceptor (PEA) traps the
  light-excited electron

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Photosystems
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Light Reactions

• Water splitting photosystem (Photosystem II)
  uses light energy to extract e- from H2O,
  releasing O2 as waste
• NADPH-producing photosystem (Photosystem I)
  transfers light-excited e- from chlorophyll to
  NADP to make NADPH
• An electron transport chain connects the two to
  make ATP

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Light Reactions
15
Calvin Cycle

• Process of synthesizing sugars
• Occurs in the stroma
• Does not require light
• Converts CO2 to sugar
• Inputs
• CO2, ATP and NADPH
• Output
• 3 carbon sugar called glyceraldehyde 3-phosphate
  (G3P) (can be used to make glucose)

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Calvin Cycle
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In the end

• A single 6-carbon sugar is formed from 6
  molecules of carbon dioxide
• Plants use the sugar for energy and to build more
  complex carbohydrates such as starches and
  cellulose
• Other organisms eat the plants and use the energy
  stored in carbohydrates

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Overview of Photosynthesis