1. Photosynthesis

2. 1.Understand that ENERGY can be transformed from one form to another. 2.Know that energy exist in two forms; free energy - available for doing work or as heat - a form unavailable for doing work. 3.Appreciate that the Sun provides most of the energy needed for life on Earth. LEARNING OBJECTIVES

3. The biomass (dry weight) of a tree comes primarily from –soil. –water. –light. –organic fertilizer (manure, detritus). –air.

4. Autotrophs sustain themselves without eating anything derived from other organisms Autotrophs are the producers of the biosphere, producing organic molecules from CO 2 and other inorganic molecules Almost all plants are photoautotrophs, using the energy of sunlight to make organic molecules Photosynthesis occurs in plants, algae, certain other protists, and some prokaryotes These organisms feed not only themselves but also most of the living world

5. Heterotrophs obtain their organic material from other organisms Heterotrophs are the consumers of the biosphere Almost all heterotrophs, including humans, depend on photoautotrophs for food and O 2 The Earth’s supply of fossil fuels was formed from the remains of organisms that died hundreds of millions of years ago In a sense, fossil fuels represent stores of solar energy from the distant past

6. Photosynthesis converts light energy to the chemical energy of food Chloroplasts are structurally similar to and likely evolved from photosynthetic bacteria The structural organization of these cells allows for the chemical reactions of photosynthesis

7. The organic carbon in a tree comes primarily from –soil. –water. –light. –organic fertilizer (manure, detritus). –air.

8. Chloroplasts: The Sites of Photosynthesis in Plants Leaves are the major locations of photosynthesis Their green color is from chlorophyll, the green pigment within chloroplasts Chloroplasts are found mainly in cells of the mesophyll, the interior tissue of the leaf Each mesophyll cell contains 30–40 chloroplasts Light Reflected light Absorbed light Transmitted light Chloroplast

9. The location and structure of chloroplasts LEAF CROSS SECTION MESOPHYLL CELL LEAF Chloroplast Mesophyll CHLOROPLAST Intermembrane space Outer membrane Inner membrane Thylakoid compartment Thylakoid Stroma Granum StromaGrana

10. Different wavelengths of visible light are seen by the human eye as different colors. WHY ARE PLANTS GREEN? Gamma rays X-raysUVInfrared Micro- waves Radio waves Visible light Wavelength (nm)

11. Why are plants green? Reflected light Transmitted light

12. What colors of light will drive photosynthesis by green plants most efficiently? a)red only b)yellow only c)green only d)blue only e)red and blue

14. Chloroplasts contain several pigments Chloroplast Pigments –Chlorophyll a –Chlorophyll b –Carotenoids Figure 7.7

15. Chlorophyll a & b Chl a has a methyl group Chl b has a carbonyl group Porphyrin ring delocalized e - Phytol tail

16. Different pigments absorb light differently

17. Excited state ee Heat Light Photon Light (fluorescence) Chlorophyll molecule Ground state 2 (a) Absorption of a photon Excitation of chlorophyll in a chloroplast  Loss of energy due to heat causes the photons of light to be less energetic.  Less energy translates into longer wavelength.  Transition toward the red end of the visible spectrum. ee

18. The Calvin cycle makes sugar from carbon dioxide –ATP generated by the light reactions provides the energy for sugar synthesis –The NADPH produced by the light reactions provides the electrons for the reduction of carbon dioxide to glucose Light Chloroplast Light reactions Calvin cycle NADP  ADP + P The light reactions convert solar energy to chemical energy –Produce ATP & NADPH AN OVERVIEW OF PHOTOSYNTHESIS

19. Figure 10.5 Reactants: Products: 6 CO 2 6 H 2 O 6 O 2 12 H 2 O C 6 H 12 O 6

20. Which experiment will produce 18 O 2 ? 1.experiment 1 2.experiment 2 3.both experiment 1 and experiment 2 4.neither experiment

21. Photosynthesis as a Redox Process Photosynthesis reverses the direction of electron flow compared to respiration Photosynthesis is a redox process in which H 2 O is oxidized and CO 2 is reduced Photosynthesis is an endergonic process; the energy boost is provided by light Energy  6 CO 2  6 H 2 O C 6 H 12 O 6  6 O 2 becomes reduced becomes oxidized

22. The Two Stages of Photosynthesis: A Preview Photosynthesis consists of the light reactions (the photo part) and Calvin cycle (the synthesis part) The light reactions (in the thylakoids) –Split H 2 O –Release O 2 –Reduce NADP + to NADPH –Generate ATP from ADP by photophosphorylation

24. The Calvin cycle (in the stroma) forms sugar from CO 2, using ATP and NADPH The Calvin cycle begins with carbon fixation, incorporating CO 2 into organic molecules

25. A Photosystem: A Reaction-Center Complex Associated with Light-Harvesting Complexes A photosystem consists of a reaction-center complex (a type of protein complex) surrounded by light-harvesting complexes The light-harvesting complexes (pigment molecules bound to proteins) transfer the energy of photons to the reaction center (a) How a photosystem harvests light Thylakoid membrane Photon Photosystem STROMA Light- harvesting complexes Reaction- center complex Primary electron acceptor Transfer of energy Special pair of chlorophyll a molecules Pigment molecules THYLAKOID SPACE (INTERIOR OF THYLAKOID) ee

26. There are two types of photosystems in the thylakoid membrane Photosystem II (PS II) functions first (the numbers reflect order of discovery) and is best at absorbing a wavelength of 680 nm The reaction-center chlorophyll a of PS II is called P680

28. Photosystem I (PS I) is best at absorbing a wavelength of 700 nm The reaction-center chlorophyll a of PS I is called P700

31. Photosystem II Photosystem I Mill makes ATP ATP NADPH ee ee ee ee ee ee ee Photon Linear Electron Flow

32. Photosynthetic bacteria that have only photosystem I 1.can split water molecules to produce oxygen. 2.cannot fix carbon dioxide. 3.generate ATP but not NADPH. 4.can reduce NADP+ to NADPH but cannot make ATP through photophosphorylation. 5.can reduce NADP+ to NADPH and make ATP through cyclic photophosphorylation.

33. Photosystem I Primary acceptor Cytochrome complex Fd Pc ATP Primary acceptor Pq Fd NADPH NADP  reductase NADP  + H  Photosystem II Cyclic Electron Flow – only PSI

34. Which evolutionary development caused the initial oxygenation of Earth’s atmosphere? 1.the evolution of the earliest photosynthetic organisms that had only PSI 2.the evolution of the first land plants 3.the evolution of the woody plants 4.the evolution of flowering plants 5.the evolution of cyanobacteria with PSI + PSII

35. Mitochondrion Chloroplast MITOCHONDRION STRUCTURE CHLOROPLAST STRUCTURE Intermembrane space Inner membrane Matrix Thylakoid space Thylakoid membrane Stroma Electron transport chain HH Diffusion ATP synthase HH ADP  P i KeyHigher [H  ] Lower [H  ] ATP Figure 10.17

36. Figure 10.18 STROMA (low H  concentration) THYLAKOID SPACE (high H  concentration) Light Photosystem II Cytochrome complex Photosystem I Light NADP  reductase NADP  + H  To Calvin Cycle ATP synthase Thylakoid membrane 2 13 NADPH Fd Pc Pq 4 H + +2 H + H+H+ ADP + P i ATP 1/21/2 H2OH2O O2O2

37. The Calvin cycle uses the chemical energy of ATP and NADPH to reduce CO 2 to sugar The Calvin cycle, like the citric acid cycle, regenerates its starting material after molecules enter and leave Carbon enters the cycle as CO 2 and leaves as a sugar named glyceraldehyde 3-phospate (G3P) For net synthesis of 1 G3P, the cycle must take place three times, fixing 3 molecules of CO 2 The Calvin cycle has three phases –Carbon fixation (catalyzed by rubisco) –Reduction –Regeneration of the CO 2 acceptor (RuBP)

42. In this diagram, compound X is the CO 2 acceptor. If CO 2 is cut off, then 1.X and 3PG will both increase. 2.X will increase, 3PG decrease. 3.X will decrease, 3PG increase. 4.X and 3PG will both decrease.

43. In this diagram, compound X is the CO 2 acceptor. If light is cut off, then 1.X and 3PG will both increase. 2.X will increase, 3PG decrease. 3.X will decrease, 3PG increase. 4.X and 3PG will both decrease.

45. The production of ATP by chemiosmosis in photosynthesis Thylakoid compartment (high H + ) Thylakoid membrane Stroma (low H + ) Light Antenna molecules Light ELECTRON TRANSPORT CHAIN PHOTOSYSTEM IIPHOTOSYSTEM IATP SYNTHASE

46. Alternative mechanisms of carbon fixation have evolved in hot, arid climates Dehydration is a problem for plants, sometimes requiring trade-offs with other metabolic processes, especially photosynthesis On hot, dry days, plants close stomata, which conserves H 2 O but also limits photosynthesis The closing of stomata reduces access to CO 2 and causes O 2 to build up These conditions favor an apparently wasteful process called photorespiration

47. Photorespiration occurs because a)rubisco can use oxygen as a substrate when CO 2 levels are low and oxygen levels are high. b)linear electron flow cannot provide the Calvin cycle with enough ATP. c)leaf cells use photorespiration to make ATP for cellular work outside the chloroplasts. d)C4 plants operate a CO 2 shuttle at a cost of extra ATP, provided by photorespiration. e)plants need a way to consume the oxygen they produce.

48. In most plants (C 3 plants), initial fixation of CO 2, via rubisco, forms a three-carbon compound (3- phosphoglycerate) In photorespiration, rubisco adds O 2 instead of CO 2 in the Calvin cycle, producing a two-carbon compound Photorespiration consumes O 2 and organic fuel and releases CO 2 without producing ATP or sugar Photorespiration may be an evolutionary relic because rubisco first evolved at a time when the atmosphere had far less O 2 and more CO 2 Photorespiration limits damaging products of light reactions that build up in the absence of the Calvin cycle In many plants, photorespiration is a problem because on a hot, dry day it can drain as much as 50% of the carbon fixed by the Calvin cycle

49. C 4 Plants C 4 plants minimize the cost of photorespiration by incorporating CO 2 into four-carbon compounds in mesophyll cells This step requires the enzyme PEP carboxylase PEP carboxylase has a higher affinity for CO 2 than rubisco does; it can fix CO 2 even when CO 2 concentrations are low These four-carbon compounds are exported to bundle-sheath cells, where they release CO 2 that is then used in the Calvin cycle

50. Figure 10.20 C 4 leaf anatomy The C 4 pathway Photosynthetic cells of C 4 plant leaf Mesophyll cell Bundle- sheath cell Vein (vascular tissue) Stoma Mesophyll cell PEP carboxylase CO 2 Oxaloacetate (4C) PEP (3C) Malate (4C) Pyruvate (3C) CO 2 Bundle- sheath cell Calvin Cycle Sugar Vascular tissue ADP ATP

51. In the last 150 years since the Industrial Revolution, CO 2 levels have risen greatly Increasing levels of CO 2 may affect C 3 and C 4 plants differently, perhaps changing the relative abundance of these species The effects of such changes are unpredictable and a cause for concern

52. CAM Plants Some plants, including succulents, use crassulacean acid metabolism (CAM) to fix carbon CAM plants open their stomata at night, incorporating CO 2 into organic acids Stomata close during the day, and CO 2 is released from organic acids and used in the Calvin cycle