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Photosynthesis: Capturing Energy

Delve into the intricate process of photosynthesis, where light energy is captured and transformed into carbohydrates by chloroplasts. Explore the roles of chlorophyll, electron transport, ATP synthesis, and the Calvin cycle in this vital metabolic pathway.

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Photosynthesis: Capturing Energy

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  1. Photosynthesis: Capturing Energy

  2. Light • Composed of photons • Visible light small portion of electromagnetic spectrum • All energy travels as waves • Shorter wavelengths have more energy than longer wavelengths

  3. Electromagneticspectrum

  4. Chloroplasts • Organelles enclosed by a double membrane • Site of photosynthesis • Located mainly within mesophyll cells inside leaf

  5. Site of photosynthesis

  6. Chlorophyll • Main photosynthetic pigment • Chlorophyll a, chlorophyll b, carotenoids, and other photosynthetic pigments are components of thylakoid membranes of chloroplasts

  7. Photosynthesis is redox process • Light energy captured and converted to carbohydrates • Hydrogens from water reduce carbon • Oxygen derived from water becomes oxidized

  8. Two phases of photosynthesis • Light-dependent • In thylakoids • Electrons energized by light generate ATP and NADPH • Carbon fixation • In stroma • Compounds generated in phase one provide energy for formation of carbohydrate

  9. Overview of photosynthesis

  10. Photosystems I and II • Two types of photosynthetic units involved in photosynthesis • Each photosystem includes • Chlorophyll molecules • Multiple antenna complexes • Photosystem I reaction center • P700 has absorption peak at 700 nm • Photosystem II reaction center • P680 has absorption peak at 680 nm

  11. Photosystem

  12. Noncyclic electron transport • ATP and NADPH formed • Electrons energized by absorption of light and pass through electron transport chain to NADP+ • Series of redox reactions • Electrons given up by P680 are replaced by electrons from photolysis of H2O

  13. Noncyclic electron transport

  14. Cyclic electron transport • Electrons from photosystem I returned to photosystem I • ATP produced by chemiosmosis • No NADPH or O2 generated

  15. ATP synthesis and electron transport • Electrons move down electron transport chain • Protons (H+) move from stroma to thylakoid lumen, creating proton gradient • Greater concentration of H+ lowers the pH

  16. Accumulation of protons in thylakoid lumen

  17. Electron transport and chemiosmosis

  18. Carbon fixation • Energy of ATP and NADPH used in formation of organic molecules from CO2 12 NADPH + 18 ATP + 6 CO2 →C6H12O6 + 12 NADP + + 18 ADP + 18 Pi + 6 H2O

  19. Three phases of Calvin cycle • CO2 uptake • Carbon reduction • RuBP regeneration

  20. Calvin cycle

  21. Summary of photosynthesis

  22. C3 and C4 plant structure compared

  23. Summaryof the C4 pathway

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