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Understanding Photosynthesis: Light-Driven CO2 Conversion to Carbohydrate

Learn about the process of photosynthesis, the significance of this vital process, its role in maintaining ecosystems, and its impact on the food chain. Explore the different stages of photosynthesis and understand the intricate workings within plant cells. Discover the importance of key pigments like chlorophyll and the absorption of light energy in driving this biological process.

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Understanding Photosynthesis: Light-Driven CO2 Conversion to Carbohydrate

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  1. Photosynthesis Process in which light energy is used to drive the conversion of CO2 to carbohydrate. 6H2O* + 6CO2 C6H12O6 + 6O2* light

  2. Importance of Photosynthesis • Source of atmospheric oxygen • Earth’s atm: 78% N2, 21% O2, 0.035% CO2 (or 350 ppm & rising) • Source of energy for food chain • photoautotrophsvs. heterotrophs • Direct/indirect involvement in all products • Maintain stable ecosystem

  3. Photosynthesis and TranspirationWhole Plant Perspective • CO2 enters leaf through open stomates; water is lost • CO2 is converted to carbohydrate (photosynthate) in the leaf and transported as sucrose in phloem • Water is taken up by roots and transported via xylem • Loss of water from the leaf via stomates is evapotranspiration

  4. Leaf Cross-Section Cuticle Epidermis guard cells & stomate Palisade parenchyma Spongy parenchyma

  5. Chloroplasts • Site of photosynthesis; several per cell • Bounded by 2 smooth membranes • Inner thylakoid membrane system • grana = stacks of thylakoids • contain PS pigments • site of light reactions • Stroma • liquid matrix • site of “dark” reactions (CO2 conversion)

  6. 3 Processes in Photosynthesis • Absorption of light energy • pigments in thylakoids • Light Reactions • pigments & proteins in thylakoids • generates ATP and NADPH • “Dark” Reactions • enzymes in stroma • reduce CO2 to carbohydrates using ATP & NADPH

  7. 3 Processes in Photosynthesis (1) lightO2CO2 sugar starch NADPH H2O ATP (2) Light Reactions (3) Dark Reactions

  8. Light Striking Leaf • Reflected back to atmosphere • Passes through leaf back to atmosphere • Absorbed by the leaf and used for PS

  9. WAVELENGTH ENERGY GAMMA RAYS X-RAYS UV V INFRARED RADIO WAVES Visible Light 380 nm 430 nm650 nm 750 nm

  10. PAR • PAR = Photosynthetically Active Radiation • 400-700 nm wavelengths • PPF = photosynthetic photon flux • PPF at full sun = 2000 µmol/m2/sec

  11. Action Spectrum Absorption Spectrum

  12. Chlorophylls Chl a Chl b Carotenoids carotenes xanthophylls Reaction Center Pigments PSI [P700] and PSII [P680] Chl a Accessory Pigments Chl a Chl b carotenes xanthophylls Photosynthetic Pigments

  13. Chlorophyll • Chl a in all higher plants • Chl b also in most higher plants • Chl c or d replaces chl b in some algae • Chl: porphyrin-like ring (loose e-’s) and phytol tail to anchor it in thylakoid membrane • Center atom of Mg surrounded by 4 N • Fe necessary for the synthesis of chl

  14. CHO Chlorophyll a polar head • Reaction Center Pigment • PSI and PSII phytol tail

  15. beta-carotene

  16. carotenoids chlorophyll thylakoid membrane

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