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Photosynthesis

Photosynthesis is a crucial process where plants convert sunlight into chemical energy. It comprises two main pathways: the light-dependent reactions (light reactions) and the light-independent reactions (dark reactions). During light reactions, sunlight is captured, oxygen is released, and energy carriers ATP and NADPH are produced. In the dark reactions, these energy carriers combine with atmospheric CO2 to form glucose, thus storing energy in plant cells. Chlorophyll and accessory pigments play vital roles in capturing light, enhancing the efficiency of this transformative process.

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Photosynthesis

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  1. Photosynthesis

  2. Introduction • 6 CO2 + 6 H2O + light energy → C6H12O6 + 6 O2 • Photosynthesis consists of two independent pathways called the light-dependent reaction (light reaction) and the light-independent reaction (dark reaction).

  3. Introduction • Light Reactions: the energy in sunlight is trapped, O2 is released, and both ATP and NADPH + H+ (hydrogen-carrier molecule) are formed • Dark Reactions: the ATP and NADPH + H+ react with CO2 from the atmosphere and form glucose • The entire process results in the transformation of light energy from the sun into energy stored in the bonds of the glucose molecule.

  4. Structure of a Chloroplast • The light reactions take place in the thylakoid membrane • The dark reactions take place in the stroma

  5. Structure of a Chloroplast

  6. Electromagnetic Spectrum

  7. Why are plants green?

  8. Pigments • Pigments are light-absorbing compounds. • Pigments appear colored because they absorb light of certain wavelengths and reflect that of others. • Chlorophyll a is the primary pigment in green plants that absorbs red and blue/violet light and reflects green light.

  9. Structure of Chlorophyll

  10. Accessory Pigments • Chloroplasts also contain other pigments called accessory pigments. • Accessory pigments trap wavelengths of light that cannot be absorbed by chlorophyll a and then transfer the energy to chlorophyll a molecules for use in photosynthesis. In this way, accessory pigments enable plants to use a greater amount of the sun’s energy than is available to chlorophyll alone.

  11. Light Reaction

  12. Light Reaction • Also called Light Dependent Reaction • Pigments that are in the chloroplasts intercept light and begin the light reactions of photosynthesis. • The light reactions occur in two photosystems (located in the thylakoid membrane): • Photosystem: a unit of several hundred chlorophyll a molecules and associated acceptor molecules -photosystem I (PSI) -photosystem II (PSII)

  13. Photosystems

  14. Excited Electrons

  15. NADPH • NADP+ is an electron acceptor • NADP+ + 2 e- + 2 H+ NADPH + H+

  16. ATP Synthase

  17. Primary Electron Acceptor ETC Proton Pump Thylakoid Water (H2O) Oxygen (O2) Hydrogen Ion (H+) Electron ATP Synthase PSI PSII Lumen

  18. Step 1

  19. Step 2

  20. Step 3

  21. Step 3

  22. Step 3

  23. Step 3

  24. Step 3

  25. Step 3

  26. ~ e low high Step 4

  27. Step 4

  28. Step 4

  29. Step 4

  30. Step 4

  31. Step 4

  32. Step 5

  33. Step 5

  34. Step 5

  35. Step 5

  36. Step 5

  37. NADP+ NADPH + H+ Step 5

  38. high low Step 6

  39. Step 6

  40. Step 6

  41. Step 6

  42. Step 6

  43. ADP + P ~ e Chemiosmosis ATP Step 6

  44. NADP+ ADP + P Reactants

  45. O2 is released into the atmosphere NADPH + H+ DR ATP Products

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