1. BIOLOGY CONCEPTS & CONNECTIONS Fourth Edition Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Neil A. Campbell Jane B. Reece Lawrence G. Mitchell Martha R. Taylor From PowerPoint ® Lectures for Biology: Concepts & Connections CHAPTER 7 Photosynthesis: Using Light to Make Food Modules 7.1 – 7.14

2. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Light is central to the life of a plant Photosynthesis is the most important chemical process on Earth –It provides food for virtually all organisms Plant cells convert light into chemical signals that affect a plant ’ s life cycle Life in the Sun

3. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Light can influence the architecture of a plant –Plants that get adequate light are often bushy, with deep green leaves –Without enough light, plants become tall and spindly with small pale leaves Too much sunlight can damage a plant –Chloroplasts and carotenoids help to prevent such damage

4. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Photosynthesis is the process by which autotrophic organisms use light energy to make sugar and oxygen gas from carbon dioxide and water AN OVERVIEW OF PHOTOSYNTHESIS Carbon dioxide WaterGlucoseOxygen gas PHOTOSYNTHESIS

5. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Plants, some protists, and some bacteria are photosynthetic autotrophs –They are the ultimate producers of food consumed by virtually all organisms 7.1 Autotrophs are the producers of the biosphere

6. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings In most plants, photosynthesis occurs primarily in the leaves, in the chloroplasts A chloroplast contains: –stroma, a fluid –grana, stacks of thylakoids The thylakoids contain chlorophyll –Chlorophyll is the green pigment that captures light for photosynthesis 7.2 Photosynthesis occurs in chloroplasts

7. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The location and structure of chloroplasts Figure 7.2 LEAF CROSS SECTION MESOPHYLL CELL LEAF Chloroplast Mesophyll CHLOROPLAST StromaGrana

8. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Intermembrane space Outer membrane Inner membrane Thylakoid compartment Thylakoid Stroma Granum

9. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The O 2 liberated by photosynthesis is made from the oxygen in water 7.3 Plants produce O 2 gas by splitting water Figure 7.3A

10. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 7.3B Figure 7.3C Experiment 1 Experiment 2 Not labeled Labeled Reactants: Products:

11. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Water molecules are split apart and electrons and H + ions are removed, leaving O 2 gas –These electrons and H + ions are transferred to CO 2, producing sugar 7.4 Photosynthesis is a redox process, as is cellular respiration Figure 7.4A Figure 7.4B Reduction Oxidation Reduction

12. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The complete process of photosynthesis consists of two linked sets of reactions: –the light reactions and the Calvin cycle The light reactions convert light energy to chemical energy and produce O 2 The Calvin cycle assembles sugar molecules from CO 2 using the energy-carrying products of the light reactions 7.5 Overview: Photosynthesis occurs in two stages linked by ATP and NADPH

13. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings An overview of photosynthesis Figure 7.5 Light Chloroplast LIGHT REACTIONS (in grana) CALVIN CYCLE (in stroma) Electrons H2OH2O O2O2 CO 2 NADP + ADP + P Sugar ATP NADPH

14. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Certain wavelengths of visible light drive the light reactions of photosynthesis 7.6 Visible radiation drives the light reactions THE LIGHT REACTIONS: CONVERTING SOLAR ENERGY TO CHEMICAL ENERGY Gamma rays X-raysUVInfrared Micro- waves Radio waves Visible light Wavelength (nm) Figure 7.6A

15. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 7.6B Light Chloroplast Reflected light Absorbed light Transmitted light

16. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Each of the many light-harvesting photosystems consists of: –an “ antenna ” of chlorophyll and other pigment molecules that absorb light –a primary electron acceptor that receives excited electrons from the reaction-center chlorophyll 7.7 Photosystems capture solar power

17. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 7.7C Primary electron acceptor Photon Reaction center PHOTOSYSTEM Pigment molecules of antenna

18. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Fluorescence of isolated chlorophyll in solution Figure 7.7A Heat Photon (fluorescence) Photon Chlorophyll molecule

19. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 7.7B Excitation of chlorophyll in a chloroplast Primary electron acceptor Other compounds Chlorophyll molecule Photon

20. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Two connected photosystems collect photons of light and transfer the energy to chlorophyll electrons The excited electrons are passed from the primary electron acceptor to electron transport chains –Their energy ends up in ATP and NADPH 7.8 In the light reactions, electron transport chains generate ATP, NADPH, and O 2

21. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Where do the electrons come from that keep the light reactions running? In photosystem I, electrons from the bottom of the cascade pass into its P700 chlorophyll

22. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Photosystem II regains electrons by splitting water, leaving O 2 gas as a by-product Figure 7.8 Primary electron acceptor Electron transport chain Electron transport Photons PHOTOSYSTEM I PHOTOSYSTEM II Energy for synthesis of by chemiosmosis

23. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The electron transport chains are arranged with the photosystems in the thylakoid membranes and pump H + through that membrane –The flow of H + back through the membrane is harnessed by ATP synthase to make ATP –In the stroma, the H + ions combine with NADP + to form NADPH 7.9 Chemiosmosis powers ATP synthesis in the light reactions

24. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The production of ATP by chemiosmosis in photosynthesis Figure 7.9 Thylakoid compartment (high H + ) Thylakoid membrane Stroma (low H + ) Light Antenna molecules Light ELECTRON TRANSPORT CHAIN PHOTOSYSTEM IIPHOTOSYSTEM IATP SYNTHASE

25. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Photosynthesis: Light Reaction http://www.youtube.com/watch?v=pE82qtKS SH4&feature=relatedhttp://www.youtube.com/watch?v=pE82qtKS SH4&feature=related http://www.youtube.com/watch?v=hj_WKgnL 6MIhttp://www.youtube.com/watch?v=hj_WKgnL 6MI

26. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Light Reactions H2OH2O

27. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Light Reactions H2OH2O

28. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Light Reactions NDAP + H + H2OH2O

29. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Light Reactions O2O2 H+H+ H+H+

30. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Light Reactions H+H+ H+H+ ADP P

31. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Light Reactions O2O2 H+H+ H+H+ NDAP + H +

32. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The Calvin cycle occurs in the chloroplast ’ s stroma –This is where carbon fixation takes place and sugar is manufactured 7.10 ATP and NADPH power sugar synthesis in the Calvin cycle THE CALVIN CYCLE: CONVERTING CO 2 TO SUGARS INPUT Figure 7.10A OUTPUT: CALVIN CYCLE

33. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The Calvin cycle constructs G3P using –carbon from atmospheric CO 2 –electrons and H + from NADPH –energy from ATP Energy-rich sugar is then converted into glucose

34. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 7.10B Details of the Calvin cycle INPUT: Step Carbon fixation. In a reaction catalyzed by rubisco, 3 molecules of CO 2 are fixed. 1 1 Step Energy consumption and redox. 2 3P P P6 6 2 ATP 6 ADP +P 6 NADPH 6 NADP + 6P G3P Step Release of one molecule of G3P. 3 CALVIN CYCLE 3 OUTPUT: 1P Glucose and other compounds G3P Step Regeneration of RuBP. 4 G3P 4 3 ADP 3ATP 3 CO 2 5P RuBP3-PGA

35. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings A summary of the chemical processes of photo- synthesis 7.11 Review: Photosynthesis uses light energy to make food molecules PHOTOSYNTHESIS REVIEWED AND EXTENDED Figure 7.11 Light Chloroplast Photosystem II Electron transport chains Photosystem I CALVIN CYCLE Stroma Electrons LIGHT REACTIONSCALVIN CYCLE Cellular respiration Cellulose Starch Other organic compounds

36. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Most plants are C 3 plants, which take CO 2 directly from the air and use it in the Calvin cycle –In these types of plants, stomata on the leaf surface close when the weather is hot –This causes a drop in CO 2 and an increase in O 2 in the leaf –Photorespiration may then occur 7.12 C 4 and CAM plants have special adaptations that save water

37. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Photorespiration in a C 3 plant CALVIN CYCLE 2-C compound Figure 7.12A

38. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Some plants have special adaptations that enable them to save water CALVIN CYCLE 4-C compound Figure 7.12B –Special cells in C 4 plants—corn and sugarcane—incorporate CO 2 into a four-carbon molecule –This molecule can then donate CO 2 to the Calvin cycle 3-C sugar

39. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The CAM plants—pineapples, most cacti, and succulents—employ a different mechanism CALVIN CYCLE 4-C compound Figure 7.12C –They open their stomata at night and make a four-carbon compound –It is used as a CO 2 source by the same cell during the day 3-C sugar Night Day