Ch. 8 Sec. 3

1. Ch. 8 Sec. 3 The Reactions of Photosynthesis

2. I. Inside a Chloroplast In plants, photosynthesis takes place inside chloroplasts Plant Chloroplast Plant cells

3. A. Chloroplasts contain thylakoids—saclike photosynthetic membranes Single thylakoid Chloroplast

4. Thylakoids are arranged in stacks known as grana. A singular stack is called a granum. Granum Chloroplast

5. B. Photosystems 1. Clusters of pigments & protein 2. Absorb light energy Photosystems Chloroplast

6. C. Two parts to photosystems 1. The light-dependent reactions a. Take place within the thylakoid membranes 2. Light-independent reactions – AKA Calvin cycle a. Takes place in the stroma - outside the thylakoid membranes

7. H2O CO2 Light NADP+ ADP + P Light- dependent reactions Calvin cycle Calvin Cycle Chloroplast Sugars O2 Fig. 8-7 page 209 The process of photosynthesis includes the light-dependent reactions as well as the Calvin cycle. What are light-dependent products?

8. II. Electron Carriers • When electrons in chlorophyll absorb sunlight, the electrons gain a great deal of energy. • Cells use electron carriers to transport these high-energy electrons from chlorophyll to other molecules.

9. A. NADP+ (nicotinamide adenine dinucleotide phosphate) 1. Accepts a. Two high-energy electrons b. Hydrogen ion (H+) 2. Converts the NADP+ into NADPH a. Traps energy of sunlight in chemical form b. Used to help build a variety of molecules the cell needs, including carbohydrates like glucose

10. III. Light-Dependent Reactions • The light-dependent reactions require light. • The light-dependent reactions produce oxygen gas and convert ADP and NADP+ into the energy carriers ATP and NADPH.

11. A. Photosynthesis begins when pigments in photosystem II absorb light, increasing the energy level of electrons Photosystem II

12. 1. These high-energy electrons are passed on to the electron transport chain. Photosystem II Electroncarriers High-energy electron

13. 2. Enzymes on the thylakoid membrane break water molecules into: a. hydrogen ions b. oxygen atoms c. energized electrons Photosystem II + O2 2H2O Electroncarriers High-energy electron

14. The energized electrons from water replace the high-energy electrons that chlorophyll lost to the electron transport chain. Photosystem II + O2 2H2O High-energy electron

15. 3. As plants remove electrons from water, oxygen is left behind and is released into the air. Photosystem II + O2 2H2O High-energy electron

16. 4. The hydrogen ions left behind when water is broken apart are released inside the thylakoid membrane. Photosystem II + O2 2H2O High-energy electron

17. B. High-energy electrons move through the electron transport chain from photosystem II to photosystem I. Photosystem II + O2 2H2O Photosystem I

18. 1. Energy from the electrons is used to transport H+ ions from the stroma into the inner thylakoid space. Photosystem II + O2 2H2O

19. C. Pigments in photosystem I use energy from light to re-energize the electrons. + O2 2H2O Photosystem I

20. NADP+ NADPH • a. gains two high-energy electrons • b. H+ ions + O2 2H2O 2 NADP+ 2 NADPH 2

21. D. As electrons are passed from chlorophyll to NADP+, more H+ ions are pumped across the membrane. + O2 2H2O 2 NADP+ 2 NADPH 2

22. 1. Soon, the inside of the membrane fills up with positively charged hydrogen ions, which makes the outside of the membrane negatively charged. + O2 2H2O 2 NADP+ 2 NADPH 2

23. 2. The difference in charges across the membrane provides the energy to make ATP + O2 2H2O 2 NADP+ 2 NADPH 2

24. E. H+ ions cannot cross the membrane directly. ATP synthase + O2 2H2O 2 NADP+ 2 NADPH 2

25. 1. The cell membrane contains a protein called ATP synthase that allows H+ ions to pass through it ATP synthase + O2 2H2O 2 NADP+ 2 NADPH 2

26. 2. As H+ ions pass through ATP synthase, the protein rotates. ATP synthase + O2 2H2O 2 NADP+ 2 NADPH 2

27. 3. As it rotates, ATP synthase binds ADP and a phosphate group together to produce ATP ATP synthase + O2 2H2O ADP 2 NADP+ 2 NADPH 2

28. Because of this system, light-dependent electron transport produces not only high-energy electrons but ATP as well. ATP synthase + O2 2H2O ADP 2 NADP+ 2 NADPH 2

29. Light-Dependent Reactions • The light-dependent reactions use water, ADP, and NADP+. • The light-dependent reactions produce oxygen, ATP, and NADPH. • These compounds provide the energy to build energy-containing sugars from low-energy compounds.

30. IV. The Calvin Cycle • The Calvin cycle uses ATP and NADPH from the light-dependent reactions to produce high-energy sugars. • Because the Calvin cycle does not require light, these reactions are also called the light-independent reactions.

31. Six carbon dioxide molecules from atmosphere 1. Combine with six 5-carbon molecules CO2 Enters the Cycle

32. 2. Forms twelve 3-carbon molecules 3. Converted into higher-energy forms.

33. C. Converted into higher-energy forms 1. The energy for this conversion comes from ATP and high-energy electrons from NADPH Energy Input 12 12 ADP 12 NADPH 12 NADP+

34. C. Two of twelve 3-carbon molecules are removed from the cycle Energy Input 12 12 ADP 12 NADPH 12 NADP+

35. 1. The molecules are used to produce sugars, lipids, amino acids and other compounds. 12 12 ADP 12 NADPH 12 NADP+ 6-Carbon sugar produced Sugars and other compounds

36. D. The 10 remaining 3-carbon molecules are converted back into six 5-carbon molecules, which are used to begin the next cycle 12 12 ADP 6 ADP 12 NADPH 6 12 NADP+ 5-Carbon MoleculesRegenerated Sugars and other compounds

37. The two sets of photosynthetic reactions work together • The light-dependent reactions trap sunlight energy in chemical form. • The light-independent reactions use that chemical energy to produce stable, high-energy sugars from carbon dioxide and water.

38. Factors Affecting Photosynthesis • Many factors affect the rate of photosynthesis, including: • Water • Temperature • Intensity of light

39. 8–3 The Reactions of Photosynthesis In plants and other photosynthetic prokaryotes, photosynthesis takes place inside the chloroplasts. Chloroplasts have saclike photosynthetic membranes called thylakoids. Proteins in the thylakoid membrane organize chlorophyll and other pigments into clusters known as photosystems. The photosystems are the light-collecting units of chlorophyll. When sunlight excites electrons in chlorophyll, the electrons gain energy. The electron transfers its energy to another molecule. The energy continues to move from molecule to molecule until it gets to the end of the chain.

40. The reactions of photosynthesis occur in two parts: light-dependent reactions and light-independent reactions. The light-dependent reactions produce oxygen gas and convert ADP and NADPinto ATP and NADPH. These reactions need light and they occur in the thylakoid membranes. The light-dependent reactions can be divided into four processes: light absorption, oxygen production, electron transport, and ATP formation. The light-dependent reactions use water, ADP, and NADP. They produce oxygen, ATP, and NADPH.

41. 2. The light-independent reactions are also called the Calvin cycle. These reactions do not need light. The Calvin cycle uses ATP and NADPH from the light-dependent reactions to produce high-energy sugars. The Calvin cycle takes place in the stroma of chloroplasts. The Calvin cycle uses carbon dioxide in its reactions. As photosynthesis proceeds, the Calvin cycleworks steadily to remove carbon dioxide from the atmosphere and turn out energy-rich sugars. Six carbon dioxide molecules are needed to make a single 6-carbon sugar.Many factors affect the rate of photosynthesis. Such factors include water availability, temperature, and the intensity of light.