Photosynthesis

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  • 1. Photosynthesis
  • 2. Energy for life processes
    •   Energy is the  ability to do work
    • Work for a cell includes  growth & repair, active transport across cell membranes, reproduction, synthesis of cellular products
    • Autotrophs or producers convert sunlight, CO2, and H2O into glucose (their food)
    • Plants, algae, and blue-green bacteria, some prokaryot es, are producers or autotrophs
    • Only 10% of the Earth’s 40 million species are autotrophs
    • Other autotrophs use  inorganic compounds instead of sunlight  to make food; process known as  chemosynthesis
    • Producers  make food for themselves and heterotrophs  (consumers that cannot make food for themselves)
    • Heterotrophs include  animals, fungi, & some bacteria, & protist s
  • 3. Light Absorption
    • Chloroplasts absorb light from the sun during the light dependent reactions
    • Photosynthetic cells may have thousands of chloroplasts
    • Chloroplasts are double membrane organelles with the an inner membrane folded into disc-shaped sacs called  thylakoids
    • Thylakoids, containing  chlorophyll  and other  accessory pigments , are in stacks called  granum  (grana, plural)
    • Grana are connected to each other & surrounded by a gel-like material called  stroma
    • Light-capturing pigments in the grana are organized into  photosystems
  • 4. Leaf Structure
    • Most photosynthesis occurs in the palisade layer.
    • Gas exchange of CO 2 and O 2 occurs at openings called stomata surrounded by guard cells on the lower leaf surface.
    Palisade Spongy
  • 5. Chloroplast Structure
    • Inner membrane called the thylakoid membrane.
    • Thickened regions called thylakoids . A stack of thylakoids is called a granum . (Plural – grana)
    • Stroma is a liquid surrounding the thylakoids.
  • 6. Pigments
    • Chlorophyll A is the most important photosynthetic pigment.
    • Other pigments called antenna or accessory pigments are also present in the leaf.
      • Chlorophyll B
      • Carotenoids (orange / red)
      • Xanthophylls (yellow / brown)
    • These pigments are embedded in the membranes of the chloroplast in groups called photosystems .
  • 7. Photosynthesis : The Chemical Process
    • Occurs in two main phases.
      • Light reactions
      • Dark reactions (aka – the Calvin Cycle)
    • Light reactions are the “photo” part of photosynthesis. Light is absorbed by pigments.
    • Dark reactions are the “synthesis” part of photosynthesis. Trapped energy from the sun is converted to the chemical energy of sugars.
  • 8. Calvin Cycle
    • Carbon atoms from CO2 are bonded or "fixed" into organic compounds during a process called  carbon fixation
    • The energy stored in ATP and NADPH during the Light Reactions is used in the Calvin cycle
    • The Calvin cycle has  3 main steps  occurring within the  stroma  of the Chloroplast
    • 1.  Carboxylation  - CO2 is covalently linked to a carbon skeleton (RuBP) 2.  Reduction  - carbohydrate is formed at the expense of ATP and NADPH 3.  Regeneration  - the CO2 acceptor RuBP reforms at the expense of ATP
  • 9. Light Reactions
    • Light-dependent reactions occur on the thylakoid membranes.
      • Light and water are required for this process.
      • Energy storage molecules are formed. (ATP and NADPH)
      • Oxygen gas is made as a waste product.
  • 10. Dark Reactions
    • Dark reactions (light-independent) occur in the stroma.
      • Carbon dioxide is “fixed” into the sugar glucose.
      • ATP and NADPH molecules created during the light reactions power the production of this glucose.
  • 11. Factors Determining the Rate of Photosynthesis
    • Light intensity - As light intensity increases, the rate of photosynthesis initially increases and then levels off to a plateau
    • Temperature - Only the dark, not the light reactions are temperature dependent because of the enzymes they use (25 oC to 37oC)
    • Length of day
    • Increasing the amount of carbon dioxide available improves the photosynthesis rate
    • Level of air pollution
  • 12. Photosynthesis in Overview
    • Process by which plants and other autotrophs store the energy of sunlight into sugars.
    • Requires sunlight, water, and carbon dioxide.
    • Overall equation:
    • 6 CO 2 + 6 H 2 0  C 6 H 12 O 6 + 6 O 2
    • Occurs in the leaves of plants in organelles called chloroplasts.