Photosynthesis

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  • Diagram to show the light dependent reactions with photosytems II and ICommonly referred to as a Z-scheme
  • P680- photosystem is sensitive to 680nm wavelength of light, P700 to 700nm of light
  • PS II produces ATP and PS I produces NADPHPhotolysis of water is associated with PS II
  • 4. Light indeprxns involve ATP/NADPH + H+/ intermediates which are made in light reactions, supply of ATP/NADPH intermediates is used up/ runs out in the dark, GP therefore not reduced/ converted to triose phosphate, RuBP therefore not regenerated, CO2 fixation therefore stops, stomata close in the dark, CO2 therefore not absorbed.
  • Photosynthesis

    1. 1. Photosynthesis
    2. 2. Structures of Photosynthesis
    3. 3. Leaves  Flattened leaf shape exposes large surface area to catch sunlight  Upper and lower leaf surfaces of a leaf comprise the epidermis  Waxy, waterproof cuticle on outer surfaces reduces water evaporation
    4. 4.  Adjustable pores called stomata allow for entry of air with CO2 Inner mesophyll cell layers contain majority of chloroplasts (40- 200 each mesophyll cell) Vascular bundles (veins) supply water and minerals to the leaf while carrying sugars away from the leaf Chloroplasts- double-membrane (inner and outer)
    5. 5. 6Chloroplast Structure
    6. 6. Pigments Pigment absorbs visible light Chlorophyll a and b absorb violet, blue, and red light but reflect green light (hence they appear green) Carotenoids absorb blue and green light but reflect yellow, orange, or red (what color would they appear?)
    7. 7. Photophosphorylation Process that creates ATP using a proton gradient created by the energy of sunlight Similar to electron transport chain in respiration Is light dependent, therefore called photophosphorylation 2 types-non-cyclic and cyclic
    8. 8. Non-cyclic photophosphorylation
    9. 9. Light Dependent Reaction
    10. 10. Path of Electron
    11. 11. Path of electron
    12. 12. Non-CyclicPhotophosphorylation ATP is generated by the protons moving across the thylakoid membranes to create a proton gradient Proton gradient is used to generate ATP during chemiosmosis NADPH2 is formed Oxygen released due to photolysis of water PSII and PSI working together Needs external source of electrons Performs best under optimum light, with CO2 present and aerobic conditions Continues to light independent reactions to fix carbon
    13. 13. Chemiosmosis Process that uses the movement of a proton (H+) to join ADP and Pi to form ATP ATP synthase is needed H+ ions create a proton-motive force
    14. 14. Cyclic Photophosphorylation Electrons are recycled, return back to PS I Proton gradient is formed, therefore ATP formation happens No reduction of NADP+ occurs, only ATP is made Requires only PS I Typical of low light situations, limited CO2 and/or anaerobic conditions Not very common, except with photosynthetic bacteria
    15. 15. Light Independent Reactions a.k.a. the Calvin Cycle
    16. 16. Light Independent Reactions CO2 diffuses into the stroma of the cloroplasts CO2 is fixed to a 5-carbon molecule (ribulose biphosphate) to form a 6 carbon molecule Rubisco, an enzyme, catalyzes this reaction 6-carbon molecule is not stable, and splits to form 3PGA Energy from ATP and NADPH is used to remove a phosphate group from 3PGA to form G3P RuBP is regenerated from G3P
    17. 17. Light Independent Reactions Occurs in the stroma Depleted carriers (ADP and NADP+) return to light- dependent reactions for recharging 6 CO2 used to synthesize 1 glucose (C6H12O6)
    18. 18. Quick Review1. How is the structure of a chloroplast related to its function?2. Why do plant cells need mitochondria if they can make ATP in chloroplasts?3. Explain the role of water in photosynthesis.4. Explain why light-independent reactions of photosynthesis can only continue for a short time in darkness.

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