Photosynthesis

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).

4. 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.

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

7. Structure of a Chloroplast

10. Electromagnetic Spectrum

11. Why are plants green?

12. 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.

13. Light Reaction

14. 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)

15. Photosystems

16. Sequence these in the order of occurrence of the light reactions: • Electrons of Photosystem II chlorophylls are excited • Electrons are transferred to NADP to form NADPH • Light strikes the leaf

17. Sequenced in the order of occurrence of the light reactions: • Light strikes the leaf • Electrons of Photosystem II chlorophylls are excited • Electrons are transferred to NADP to form NADPH

19. Excited Electrons

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

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

23. Dark Reaction

24. Dark Reaction • The dark reaction is also known as the Calvin Cycle, after an American scientist (Melvin Calvin) who figured out the pathway. • The dark reaction is also known as the C3 Cycle because the first stable products of this pathway are molecules that contain three carbon atoms. • The Calvin Cycle occurs in the stroma.

25. 6 CO2 C unstable compound 6 RuBP C C C C C C C C C C C C C C C C C C C C C C C C C C 12 PGA Glucose 12 PGAL 2 PGAL 6 ATP ~ e 12 ATP 6 ADP + P ~ e 10 PGAL 12 ADP + P 12 NADPH + H+ e- 12 NADP+

28. Cells convert the storage bond energy to the phosphate bonds of ATP in the process of respiration.

29. ATP Adenosine triphosphate

32. ATP – P = ADP • ADP + P = ATP

33. Adenosine Diphosphate 7.3 kcal/mole energy released

34. Adenosine Monophosphate

35. Adenosine Diphosphate 7.3 kcal/mole energy released

36. Adenosine Triphosphate

37. T/F Questions • ATP has more energy than ADP.

38. T/F • There are three phosphate atoms in ATP?

39. T/F • You are storing energy right now in your body in the phosphate bonds of ATP.

40. T/F • ATP is made of a sugar, the base adenine and a phosphate.

41. Stomata