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Photosynthesis!!!!

Photosynthesis!!!!. Photosynthesis is divided into two parts. The overall reaction in photosynthesis:. Light energy. 6CO 2. 12 H 2 O. C 6 H 12 O 6. 6O 2. 6 H 2 O. +. +. +. +. Two components:. Light-dependent reactions. Light-independent reactions. Chemical energy

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Photosynthesis!!!!

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  1. Photosynthesis!!!!

  2. Photosynthesis is divided into two parts The overall reaction in photosynthesis: Light energy 6CO2 12 H2O C6H12O6 6O2 6 H2O + + + + Two components: Light-dependent reactions Light-independent reactions Chemical energy (ATP, NADPH) Chemical energy (ATP, NADPH) Chemical energy (C6 H12O6) Light energy O2 H2O CO2 Energy Harvest Synthesis

  3. Figure 10.4 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle (Layer 3)

  4. Photosynthesis starts in the thylakoid membrane These aggregations of pigment molecules are called photosystems

  5. Figure 10.11 How a photosystem harvests light

  6. The energy from light is captured and converted in chloroplasts • Energy from light excites an electron in chlorophyll. This electron is then passed to acceptor molecules to be used to make ATP and NADPH Stroma Light photon Electron acceptor molecule e- Reaction center (chlorophyll a ) Thylakoid Thylakoid space Chloroplast Photosystem Stroma

  7. There are 2 types of reaction centers in green algae and plants: Photosystem I: activated by light of wavelengths of 700nm Photosystem II: activated by light of wavelengths of 680nm These photosystems are named after the order in which they were discovered, not the order in which they act during photosynthesis

  8. Noncyclic electron flow during the light reactions generates ATP and NADPH

  9. The electrons in photosystem II are replaced by electrons from water

  10. The electrons from chlorophyll are passed to an ETC which makes ATP

  11. The electrons reach photosystem I where another photon of light excites them once again

  12. The electrons from photosystem II are passed down a second ETC, in which they are used to make NADPH

  13. Figure 10.13 A mechanical analogy for the light reactions

  14. Figure 10.16 The light reactions and chemiosmosis: the organization of the thylakoid membrane

  15. Figure 10.15 Comparison of chemiosmosis in mitochondria and chloroplasts

  16. Sometimes an alternate pathway happens In cyclic electron transport, which drives cyclic photophosphorylation, photosystem I transfers electrons to plastoquinone (PQ).

  17. Summary of the Light Dependent Reaction of Photosynthesis • Light energy is absorbed by chlorophyll molecules, which excites electrons • The energy from the excited electrons is converted to chemical energy: • Photosystem II: • electron transport chain produces ATP • The excited electrons are replaced by splitting a water molecule, releasing O2 • Photosystem I: • The excited electron is donated to NADP+ to produce NADPH

  18. Photosynthesis is a two-step process • The light independent reactions (Calvin cycle) use the energy in ATP and NADPH to reduce organic compounds to form glucose.

  19. Figure 10.17 The Calvin cycle (Layer 1)

  20. Figure 10.17 The Calvin cycle (Layer 2)

  21. Figure 10.17 The Calvin cycle (Layer 3)

  22. Summary • Light Dependent Reaction • Light + chlorophyll --> ATP + NADPH + (O2 as waste) • Light Independent Reaction (Calvin Cycle) • CO2 + ATP + NADPH --> glucose

  23. What happens to the glucose produced by photosynthesis? Sucrose CH2OH O O HOCH2 H H H H HO OH H O H CH2OH HO H OH HO H Fructose subunit Glucose subunit

  24. Starch CH2OH CH2OH CH2OH O O O H H H H H H Up to 1000or moremonomers H H H OH OH H H H OH O O O O OH H OH H OH H Glucosesubunit Glucosesubunit Glucosesubunit

  25. MMM… Starch

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