1. Photosynthesis Mader Ch. 8

2. Photosynthetic Organisms Algae PlantsAutotrophs Cyanobacteria EK 2A2e: Photosynthesis first evolved in prokaryotic organisms - these were responsible for an oxygen atmosphere - these pathways were the foundation for eukaryotic photosynthesis

3. Please Note Chemosynthetic organisms are also autotrophs but capture free energy from inorganic molecules in the environment – this does not require O 2

4. Energy Flow – 1 st Law of Thermodynamics Photosynthetic Organisms capture free energy: –Absorb light energy –Transform light energy into stored chemical energy (ie. carbohydrate bonds, etc.) All living organisms require stored chemical energy to live! Heterotrophic Organisms capture free energy: – Can’t convert light energy – Consume carbohydrates as food – Can metabolize carbohydrates, lipids and prteins by hydrolysis as sources of free energy. Both convert stored energy to ATP

5. Chloroplasts Specialized organelles that compartmentalize the process of photosynthesis. – gather the sun's free energy with light-absorbing molecules called pigments. – main pigment in plants is chlorophyll. There are two main types of chlorophyll: – chlorophyll a – chlorophyll b

7. Copyright Pearson Prentice Hall Light and Pigments Light is a form of energy – any compound that absorbs light = absorbs energy When chlorophyll absorbs light, much of the free energy is transferred directly to electrons in the chlorophyll molecule, raising the energy levels of these electrons. These high-energy electrons are what make photosynthesis work.

8. Chloroplasts Structure – Double outer membrane – compartmentalizes reactions/processes – Membrane-bound thylakoids Organized in stacks – grana – Stroma – semi-fluid interior of the chloroplast

9. Leaves and Photosynthesis 9 Grana Chloroplast Leaf cross section granum independent thylakoid in a granum mesophyll lower epidermis upper epidermis cuticle leaf vein outer membrane inner membrane thylakoid space thylakoid membrane overlapping thylakoid in a granum CO 2 O2O2 stoma stroma 37,000 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. © Dr. George Chapman/Visuals Unlimited

10. Photosynthesis The raw materials for photosynthesis are carbon dioxide and water  Roots absorb water that moves up vascular tissue  Carbon dioxide enters a leaf through small openings called stomata and diffuses into chloroplasts in mesophyll cells

11. Overview of Photosynthesis 11 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. thylakoid membrane

12. Overview of Photosynthesis 12 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. solar energy thylakoid membrane

13. Overview of Photosynthesis 13 solar energy thylakoid membrane Light reactions ADP + NADP + H2OH2O Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

14. Overview of Photosynthesis 14 O2O2 solar energy thylakoid membrane Light reactions ADP + NADP + NADPH ATP H2OH2O Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

15. Overview of Photosynthesis 15 CO 2 CH 2 O stroma Calvin cycle reactions O2O2 solar energy thylakoid membrane Light reactions ADP + P NADP + NADPH ATP H2OH2O Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

16. Photosynthesis Equation 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2 carbon dioxide + water sugars + oxygen Photosynthesis uses the energy of sunlight to convert water and carbon dioxide into high-energy sugars and oxygen. Light

17. Copyright Pearson Prentice Hall Light-Dependent Reaction The light-dependent reaction requires light. The light-dependent reactions produce oxygen gas and convert ADP and NADP + into the energy carriers ATP and NADPH.

18. Copyright Pearson Prentice Hall Light-Dependent Reactions takes place in the thylakoid of the chloroplasts. - use proteins embedded in the membrane

19. Copyright Pearson Prentice Hall Photosystem II Photosynthesis begins when pigments in photosystem II absorb light energy. The light energy is absorbed by electrons, increasing their energy level.

20. Copyright Pearson Prentice Hall Photosystem II These high-energy electrons are passed on to the electron transport chain. Electron carriers High-energy electron

21. Copyright Pearson Prentice Hall Photosystem II 2H 2 O Enzymes on the thylakoid membrane break water molecules into: Electron carriers High-energy electron Photosystem II

22. Copyright Pearson Prentice Hall Photosystem II 2H 2 O – hydrogen ions – oxygen atoms – energized electrons + O 2 Electron carriers High-energy electron

23. Copyright Pearson Prentice Hall Photosystem II 2H 2 O + O 2 The energized electrons from water replace the high- energy electrons that chlorophyll lost to the electron transport chain. High-energy electron

24. Copyright Pearson Prentice Hall Photosystem II 2H 2 O As plants remove electrons from water, oxygen is left behind and is released into the air. + O 2 High-energy electron

25. Copyright Pearson Prentice Hall Photosystem II 2H 2 O The hydrogen ions left behind are released into the inside of the thylakoid. + O 2 High-energy electron

26. Copyright Pearson Prentice Hall Photosystem II 2H 2 O Energy from the electrons passing through membrane proteins is used to transport H + ions from the stroma into the inner thylakoid space. – Active Transport + O 2

27. Copyright Pearson Prentice Hall Photosystem II 2H 2 O High-energy electrons move through the Electron Transport Chain from photosystem II to photosystem I. + O 2 Photosystem I Photosystem II

28. Copyright Pearson Prentice Hall 2H 2 O When light energy hits Photosystem I, energized electrons leave the system and are accepted by electron acceptors. + O 2 Photosystem I

29. Copyright Pearson Prentice Hall 2H 2 O NADP + then picks up these high-energy electrons, along with H + ions, and becomes NADPH. + O 2 2 NADP + 2 NADPH 2

30. Copyright Pearson Prentice Hall 2H 2 O + O 2 2 NADP + 2 NADPH 2

31. Copyright Pearson Prentice Hall 2H 2 O When electrons are passed through the Electron Transport Chain, an electrochemical gradient (or proton gradient) of H+ ions across the thylakoid membrane is established. + O 2 2 NADP + 2 NADPH 2

32. Copyright Pearson Prentice Hall 2H 2 O Potential Energy: The difference in charges across the membrane provides the energy to make ATP + O 2 2 NADP + 2 NADPH 2

33. Copyright Pearson Prentice Hall 2H 2 O H + ions cannot cross the membrane directly. + O 2 ATP synthase 2 NADP + 2 NADPH 2

34. Copyright Pearson Prentice Hall 2H 2 O The cell membrane contains the enzyme ATP Synthase that allows H + ions to pass through it + O 2 ATP synthase 2 NADP + 2 NADPH 2

35. Copyright Pearson Prentice Hall 2H 2 O The movement of H + ions as they pass through ATP Synthase powers the building of ATP from ADP and Pi + O 2 ATP synthase 2 NADP + 2 NADPH 2

36. Copyright Pearson Prentice Hall 2H 2 O This is called chemiosmosis + O 2 2 NADP + 2 NADPH 2 ATP synthase ADP

37. Copyright Pearson Prentice Hall 2H 2 O Because of this system, light-dependent electron transport produces not only high-energy electrons but ATP – both are sent to the CALVIN CYCLE + O 2 ATP synthase ADP 2 NADP + 2 NADPH 2

38. Review The thylakoid space acts as a reservoir for hydrogen ions (H + ) Each time water is oxidized, two H + remain in the thylakoid space Transfer of electrons in the electron transport chain yields energy –Used to pump H + across the thylakoid membrane –Protons move from stroma into the thylakoid space Flow of H + back across the thylakoid membrane –Energizes ATP synthase, which –Enzymatically produces ATP from ADP + P i This method of producing ATP is called chemiosmosis Photosystem I and II are embedded in the thylakoid membrane and are connected by the transfer of e-’s

39. Reactants of The Light Dependent Reaction (ETC) Water ADP and P NADP+ and H+

40. Products of the Light-Dependent Reaction (ETC) The electron transport chain produces: – Oxygen from the breakdown of water – NADPH from NADP+ and H+ (+energy from electrons) – ATP from ADP Through the ATP synthase protein as H+ pass from one side of the thylakoid membrane to the other The NADPH and ATP are used in the Calvin Cycle

41. Connections: Be able to explain how internal membranes and organelles contribute to cell function!

42. Plants as Carbon Dioxide Fixers A cyclical series of reactions – CALVIN CYCLE Utilizes atmospheric carbon dioxide to produce carbohydrates Known as C 3 photosynthesis CO 2 undergoes carbon dioxide fixation which produces carbohydrates. –These carbohydrates can be used to make fatty acids/glycerol for oils, glucose, fructose, starch, cellulose, amino acids This cycle is powered by the ATP and NADPH from the Light Dependent Reaction –ADP and NADP+ form which are recycled back to the LDR to pick up energy and electrons. 42

43. The Calvin Cycle Reactions 43 P P H2OH2OCO 2 solar energy Calvin cycle ADP + NADP + Light reactions NADPH ATP CH 2 O O2O2 stroma These ATP molecules were produced by the light reactions. Other organic molecules Glucose net gain of one G3P 6 3PG C 3 intermediate 3 RuBP C 5 5 G3P C 3 6 BPG C 3 G3P glyceraldehyde-3-phosphate BPG 1,3-bisphosphoglycerate 3PG 3-phosphoglycerate RuBP ribulose-1,5-bisphosphate Metabolites of the Calvin Cycle 3 ADP + 3 3 ATP 6 NADP + 6 G3P C 3 regeneration of RuBP Calvin cycle CO 2 reduction CO 2 fixation 6 NADPH 3CO 2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3 C 6 These ATP and NADPH molecules were produced by the light reactions. 6 ATP 6 ADP + 6 P

44. Fate of G3P 44 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sucrose (in leaves, fruits, and seeds) G3P amino acid synthesis glucose phosphate fatty acid synthesis + fructose phosphate Cellulose (in trunks, roots, and branches) Starch (in roots and seeds) © Herman Eisenbeiss/Photo Researchers, Inc.

45. Other Types of Photosynthesis - Adaptations In hot, dry climates –Stomata must close to avoid wilting –CO 2 decreases and O 2 increases –O 2 starts combining with RuBP, leading to the production of CO 2 –This is called photorespiration C 4 plants solve the problem of photorespiration –Fix CO 2 to PEP (a C 3 molecule) –The result is oxaloacetate, a C 4 molecule –In hot & dry climates C 4 plants avoid photorespiration Net productivity is about 2-3 times greater than C 3 plants in hot/dry environments –In cool, moist environments, C 4 plants can’t compete with C 3 plants

46. CO 2 Fixation in C 3 and C 4 Plants 46 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. C4C4 CO 2 RuBP Calvin cycle 3PG mesophyll cell G3P a. CO 2 fixation in a C 3 plant, wildflowers CO 2 mesophyll cell CO 2 Calvin cycle bundle sheath cell G3P b. CO 2 fixation in a C 4 plant, corn, Zea mays a: © Brand X Pictures/PunchStock RF; b: Courtesy USDA/Doug Wilson, photographer

47. Other Types of Photosynthesis CAM Photosynthesis –Crassulacean-Acid Metabolism –CAM plants partition carbon fixation by time During the night –CAM plants fix CO 2 –Form C 4 molecules, which are –Stored in large vacuoles During daylight –NADPH and ATP are available –Stomata are closed for water conservation –C 4 molecules release CO 2 to Calvin cycle 47

48. CO 2 Fixation in a CAM Plant 48 Calvin cycle CO 2 C4C4 G3P CO 2 fixation in a CAM plant, pineapple, Ananas comosus night day Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. © S. Alden/PhotoLink/Getty Images.

49. Adaptations of Plants Each method of photosynthesis has advantages and disadvantages –Depends on the climate C 4 plants most adapted to: –High light intensities –High temperatures –Limited rainfall C 3 plants better adapted to –Cold (below 25°C) –High moisture CAM plants are better adapted to extreme aridity –CAM occurs in 23 families of flowering plants –Also found among nonflowering plants 49

50. Connection EK 1C3a: Scientific evidence supports the idea that evolution has occurred in all species – The student is able to describe a model that represents evolution within a population.