1. Chapter 7~ Photosynthesis

2. Photosynthesis in nature Autotrophs: biotic producers; photoautotrophs; chemoautotrophs; obtains organic food without eating other organisms Heterotrophs: biotic consumers; obtains organic food by eating other organisms or their by- products (includes decomposers)

3. The chloroplast Sites of photosynthesis Pigment: chlorophyll Plant cell: mesophyll Gas exchange: stomata Double membrane Thylakoids, grana, stroma

5. Leaves and Photosynthesis 5 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

6. 7.2 The Process of Photosynthesis Light Reactions – take place only in the presence of light –Energy ‑ capturing reactions –Chlorophyll absorbs solar energy –This energizes electrons –Electrons move down an electron transport chain Pumps H + into thylakoids Used to make ATP out of ADP and NADPH out of NADP Calvin Cycle Reactions – take place in the stroma –CO 2 is reduced to a carbohydrate –Use ATP and NADPH to produce carbohydrate 6

7. Photosynthetic Pigments and Photosynthesis 7 Wavelengths (nm) Increasing wavelength a. The electromagnetic spectrum includes visible light.b. Absorption spectrum of photosynthetic pigments. Increasing energy Gamma rays X raysUVInfrared Micro- waves Radio waves visible light 500600750 Wavelengths (nm) 380500600750 chlorophyll a chlorophyll b carotenoids Relative Absorption Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

8. Electromagnetic Spectrum Visible Light – only a small portion of the spectrum, but it is the radiation that drives photosynthesis. Photons – fixed amounts of energy, non- tangible objects. Amount of energy is inversely related to wavelength

9. Photons and Energy When pigments (ex. Chlorophyll) absorb photons, the energy has to go somewhere. The electrons of a pigment jump to an excited state and absorb the photon. The electrons will then have potential energy, but will be very unstable so will fall back to the ground state and when they fall they release energy as heat.

10. Plants as Solar Energy Converters The light reactions consist of two alternate electron pathways: –Noncyclic pathway –Cyclic pathway Capture light energy with photosystems –Pigment complex helps collect solar energy like an antenna –Occur in the thylakoid membranes Both pathways produce ATP The noncyclic pathway also produces NADPH 10

11. Photosystems Light harvesting units of the thylakoid membrane Composed mainly of protein and pigment antenna complexes Antenna pigment molecules are struck by photons Energy is passed to reaction centers (redox location) Excited e- from chlorophyll is trapped by a primary e- acceptor

12. Figure 10.6 Why leaves are green: interaction of light with chloroplasts

13. Photosystem I & II Photosystem I – the reaction center is known as P700 because it best absorbs light at 700nm Photosystem II – the reaction center is known as P680 because it absorbs light best at 680nm The two pigments are actually the same, but are associated with different proteins so work differently

14. Noncyclic electron flow Photosystem II (P680): – photons excite chlorophyll e- to an acceptor – e- are replaced by splitting of H2O (release of O2) –e-’s travel to Photosystem I down an electron transport chain –as e- fall, ADP  ATP (noncyclic photophosphorylation) Photosystem I (P700): –‘fallen’ e- replace excited e- to primary e- acceptor –2nd ETC ( Fd~NADP+ reductase) transfers e- to NADP+  NADPH (...to Calvin cycle…) These photosystems produce equal amounts of ATP and NADPH

15. Figure 10.12 How noncyclic electron flow during the light reactions generates ATP and NADPH (Layer 1)

16. Figure 10.12 How noncyclic electron flow during the light reactions generates ATP and NADPH (Layer 2)

17. Figure 10.12 How noncyclic electron flow during the light reactions generates ATP and NADPH (Layer 3)

18. Figure 10.12 How noncyclic electron flow during the light reactions generates ATP and NADPH (Layer 4)

19. Figure 10.12 How noncyclic electron flow during the light reactions generates ATP and NADPH (Layer 5)

20. Chemiosmosis Chloroplasts and Mitochondria generate ATP through chemiosmosis. Just like we learned in Chapter 9 in the electron transport chain and oxidative phosphorylation, the chloroplasts do this much the same way except for: In cellular respiration the e- dropped down the etc came from food molecules. In chloroplasts the e- came from captured light. Meaning the mitochondria transforms chemical energy from food molecules to ATP, and chloroplasts transform light energy into chemical energy. In mitochondria the protons were pumped into the intercellular matrix then back into the mitochondrial matrix. In chloroplasts the protons are pumped into the thylakoid space and then back into the stroma, so ATP is made in the stroma where it is used to drive sugar synthesis during the Calvin cycle. D:\ImageLibrary1-17\10- Photosynthesis\10-17- LightReactions.mov

21. Figure 10.15 Comparison of chemiosmosis in mitochondria and chloroplasts

22. Figure 10.16 The light reactions and chemiosmosis: the organization of the thylakoid membrane

23. Organization of a Thylakoid 23 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. H+H+ H+H+ P e-e- O2O2 2 + 2 1 P H2OH2O CO 2 solar energy thylakoid thylakoid membrane thylakoid space NADPH ATP Stroma chemiosmosis ATP synthase e-e- NADP + granum photosystem II stroma + ADP H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H2OH2O electron transport chain e-e- thylakoid membrane Calvin cycle reactions ADP + NADP + Light reactions NADPH ATP CH 2 O O2O2 photosystem I NADP reductase H+H+ Thylakoid space H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ Pq e-e- e-e-

24. 24 Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.

25. The Calvin cycle 3 molecules of CO2 are ‘fixed’ into glyceraldehyde 3- phosphate (G3P) Phases: –1- Carbon fixation~ each CO2 is attached to RuBP (rubisco enzyme) –2- Reduction~ electrons from NADPH reduces to G3P; ATP used up –3- Regeneration~ G3P rearranged to RuBP; ATP used; cycle continues D:\ImageLibrary 1-17\10- Photosynthesis\10 -16- CalvinCycle.mov

26. 26 Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.

27. Calvin cycle

28. Calvin Cycle, net synthesis For each G3P (and for 3 CO2)……. Consumption of 9 ATP’s & 6 NADPH (light reactions regenerate these molecules) G3P can then be used by the plant to make glucose and other organic compounds

29. Cyclic electron flow Alternative cycle when ATP is deficient Photosystem I used but not II; produces ATP but no NADPH Why? The Calvin cycle consumes more ATP than NADPH……. Cyclic photophosphorylation

30. Fate of G3P 30 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.

31. 7.5 Other Types of Photosynthesis 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 cool, moist environments, C 4 plants can’t compete with C 3 plants 31

32. Chloroplast Distribution in C 4 vs. C 3 Plants 32 C 3 Plant C 4 Plant bundle sheath cell bundle sheath cell mesophyll cells vein stoma Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

33. CO 2 Fixation in C 3 and C 4 Plants 33 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

34. 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 34

35. CO 2 Fixation in a CAM Plant 35 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.

36. Other Types of Photosynthesis 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 36

37. A review of photosynthesis