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Photosynthesis

Learn about photosynthesis, its key steps including light and dark reactions, and the role of chloroplast structures like thylakoids. Discover the detailed process of converting sunlight into chemical energy to produce sugars.

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Photosynthesis

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  1. Photosynthesis

  2. Photosynthesis Equation • CO2 + H2O + SUN  C6H12O6 + O2

  3. Photosynthesis occurs in the chloroplasts

  4. Structures inside chloroplasts where process of photosynthesis takes place are Thylakoids • Grana – Stacks of thylakoids • Stroma – The fluid surrounding thylakoid

  5. There are 2 basic steps for photosynthesis • 1) Light reactions • 2) Dark reactions (light independent reactions) (or Calvin cycle)

  6. Light reactions convert light energy to chemical energy (ATP & NADPH) • Dark reactions (Calvin Cycle) turn chemical energy into Sugars

  7. Light reactions Occur in the Thylakoid membrane • Have two parts: a) Photosystem II (PSII) b) Photosystem I (PSI)

  8. Photosystem II (comes first) A) Sunlight hits Chlorophyll A and transfers energy to the reaction center (another Chlorophyll molecule)

  9. Photosystem II B) This releases electrons which travel through molecules in the electron transport chain (ETC) ending at PSI PS I PS II

  10. Photosystem II C) An enzyme splits water into protons, electrons and oxygen. This provides more electrons to travel to PSI

  11. PSII

  12. Water reaction in PSII 2H20  4 H+ + 4 e- + O2 Protons (H+) Will be used later in PSI Electrons (e-) – Move along ETC to PSI Oxygen (O2) – Released as a gas, NOT needed

  13. Photosystem I (comes 2nd) A) Electrons from ETC reach PSI reaction center in a second molecule of Chlorophyll A

  14. Photosystem I B) Sun helps electrons go through a 2nd Electron transport chain (ETC) in membrane and Causing NADP+ to turn into NADPH

  15. H+ Photosystem I C) ATP synthase pushes protons (H+) out of membrane to make ATP

  16. Reduction of NADPH • NADP+ is reduced by electrons and protons that were produced by the water splitting • NADP+ + e- + H+ NADPH

  17. Formation of ATP The enzyme ATP synthase uses H+ energy to produce ATP ADP + P + Energy  ATP

  18. Summary of light reactions • H20 + sunlight + NADP+ + ADP  O2 + NADPH + ATP • The energy molecules NADPH and ATP can not be stored for long. • They will be used in Dark reactions to make sugar

  19. Dark reactions (Calvin Cycle) • Occurs in Stroma • Called Light independent reactions • They do not need light, but they need the ATP and NADPH from the light reactions

  20. Calvin Cycle • If there is no light, The Calvin Cycle soon uses up its ATP and NADPH and stops working. • LIKE a car, will drive for a while, but must fill up sometime

  21. Calvin Cycle • The process of using ATP and NADPH energy to join CO2 into sugars

  22. Calvin Cycle Steps (C3 plants) A) Carbon Fixation A molecule of CO2 combines with RuBP(enzyme = Rubisco) then splits into 2 PGA molecules

  23. Calvin Cycle Steps (C3) B) Reduction - ATP and NADPH are used to form GP3, 3 carbon sugar

  24. Calvin Cycle Steps (C3) C) Regeneration of RuBP - 5 of the 6 Carbons reform into RuBP prepare for next CO2

  25. Calvin Cycle Steps (C3) 3 turns of the cycle produce one 3 carbon sugar. 6 turns forms 1 glucose

  26. Summary of Dark Reactions • CO2 + NADPH + ATP  Sugar + NADP+ + ADP + P

  27. The dark reactions are called the light dependant reactions because they depend on the ATP and NADPH produced in the light reactions

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