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Where It Starts – Photosynthesis Chapter 7 Hsueh-Fen Juan Oct. 02 & 09, 2012.

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Presentation on theme: "Where It Starts – Photosynthesis Chapter 7 Hsueh-Fen Juan Oct. 02 & 09, 2012."— Presentation transcript:

1 Where It Starts – Photosynthesis Chapter 7 Hsueh-Fen Juan Oct. 02 & 09, 2012

2 ABC video: Solar Power

3 Impacts, Issues: Biofuels  Coal, petroleum, and natural gas were once ancient forests, a limited resource; biofuels from wastes are a renewable resource

4 7.1 Sunlight as an Energy Source  Photosynthetic organisms use pigments to capture the energy of sunlight  Photosynthesis The synthesis of organic molecules from inorganic molecules using the energy of light 光合作用定義:利用光能將無機分子轉變為有機分 子的代謝途徑

5 Properties of Light  Visible light is part of an electromagnetic spectrum of energy radiating from the sun Travels in waves Organized into photons  Wavelength The distance between the crests of two successive waves of light (nm)

6 Electromagnetic Spectrum of Radiant Energy

7 The Rainbow Catchers  Different wavelengths form colors of the rainbow Photosynthesis uses wavelengths of 380-750 nm  Pigment An organic molecule that selectively absorbs light of specific wavelengths  Chlorophyll a The most common photosynthetic pigment Absorbs violet and red light (appears green) 因此平常葉子呈綠色即因葉綠素含量豐富之故,但 一到秋天,葉綠素大量破壞流失,其他色素反而較 穩定,因此葉子呈現黃、紅等色

8 Photosynthetic Pigments  Collectively, chlorophyll and accessory pigments absorb most wavelengths of visible light  The light-trapping part of a pigment is an array of atoms, and electrons of these atoms occupy one large orbital that spans all of the atoms  Electrons in such arrays in pigment molecules absorb photons of light energy, boosting electrons to a higher energy level  Energy is captured and used for photosynthesis

9 Some Pigments in Photosynthesizers

10 Two Photosynthetic Pigments

11 7.2 Exploring the Rainbow  Engelmann identified colors of light that drive photosynthesis (violet & red, 光合色素所吸收的 ) by using a prism to divide light into colors Algae ( 藻類 ) using these wavelengths gave off the most oxygen ( 使用好氧菌來測試 )  An absorption spectrum ( 吸收光譜 ) shows which wavelengths a pigment absorbs best Organisms in different environments use different pigments ( 地球不同地方能收到的陽光波長也不同 ) 為啥藻類喜歡吸收 500-600nm 的光?因為海水對 此波長的光吸收率最差,因此,水生藻類大多富含 能吸收此段波長光的光合色素

12 Photosynthesis and Wavelengths of Light

13 7.1-7.2 Key Concepts: The Rainbow Catchers  The flow of energy through the biosphere starts when chlorophylls and other photosynthetic pigments absorb the energy of visible light

14 7.3 Overview of Photosynthesis  Chloroplast An organelle that specializes in photosynthesis in plants and many protists  Stroma A semifluid matrix surrounded by the two outer membranes of the chloroplast Sugars are built in the stroma Stroma contains DNA and some ribosomes

15 Overview of Photosynthesis  Thylakoid membrane ( 囊狀膜 ) Folded membrane that make up thylakoids ( 葉綠 囊 ) The space inside all of the disks is a single, continuous compartment Contains clusters of light-harvesting pigments that absorb photons of different energies  Photosystems (type I and type II) Groups of molecules that work as a unit to begin the reactions of photosynthesis Convert light energy into chemical energy

16 Overview of Photosynthesis  Light-dependent reactions Light energy is transferred to ATP and NADPH Water molecules are split, releasing O 2  Light-independent reactions Energy in ATP and NADPH drives synthesis of glucose and other carbohydrates from CO 2 and water

17 Animation: Photosynthesis overview

18 Summary: Photosynthesis

19 Sites of Photosynthesis in Plants

20 Fig. 7-5a, p. 111

21 Fig. 7-5b, p. 111

22 Fig. 7-5c, p. 111

23 Animation: Sites of photosynthesis

24 7.4 Light-Dependent Reactions  In the first stage of photosynthesis, light energy drives electrons out of photosystems  The electrons may be used in a noncyclic or cyclic pathway of ATP formation

25 Capturing Energy for Photosynthesis  Photons boost electrons in pigments to higher energy levels  Light-harvesting complexes absorb the energy  Electrons are released from special pairs of chlorophyll a molecules in photosystems

26 The Thylakoid Membrane

27 Cyclic and Noncyclic Pathways  Electrons from photosystems take noncyclic or cyclic pathways, forming ATP

28 Replacing Lost Electrons  Electrons lost from photosystem II are replaced by photolysis of water molecules, which dissociate into hydrogen ions and oxygen  Photolysis ( 光解 ) Process by which light energy breaks down a molecule such as water

29 Electron Flow in a Noncyclic Pathway  Electrons lost from a photosystem enter an electron transfer chain in the thylakoid membrane  Electron transfer chains Organized arrays of enzymes, coenzymes, and other proteins that accept and donate electrons in a series 分清楚: light-harvesting complex 和 electron transfer chains

30 Harvesting Electron Energy  Light energy is converted to chemical energy Entry of electrons from a photosystem into the electron transfer chain is the first step in light- dependent reactions  ATP forms in the stroma Electron energy is used to build up a H + gradient across the membrane H + flows through ATP synthase (ATP 合成酶 ), which attaches a phosphate group to ADP ATP synthase is a membrane transport protein (H + cannot simply diffuse through a lipid bilayer )

31 Fig. 7-8, p. 113 to second stage of reactions The Light-Dependent Reactions of Photosynthesis ATP synthase light energy NADPH ATP ADP + P i photosystem II electron transfer chain photosystem I thylakoid compartment stroma A Light energy drives electrons out of photosystem II. C Electrons from photosystem II enter an electron transfer chain. E Light energy drives electrons out of photosystem I, which accepts replacement electrons from electron transfer chains. G Hydrogen ions in the thylakoid compartment are propelled through the interior of ATP synthases by their gradient across the thylakoid membrane. B Photosystem II pulls replacement electrons from water molecules, which dissociate into oxygen and hydrogen ions (photolysis). The oxygen leaves the cell as O 2. D Energy lost by the electrons as they move through the chain causes H + to be pumped from the stroma into the thylakoid compartment. An H + gradient forms across the membrane. F Electrons from photosystem I move through a second electron transfer chain, then combine with NADP + and H +. NADPH forms. H H + flow causes the ATP synthases to attach phosphate to ADP, so ATP forms in the stroma. NADP + Noncyclic Pathway of Photosynthesis

32 Electron Flow in a Cyclic Pathway 

33 7.5 Energy Flow in Photosynthesis  Energy flow in the light-dependent reactions is an example of how organisms harvest energy from their environment

34 Photophosphorylation 

35 Energy Flow in Light-Dependent Reactions

36 Fig. 7-9a, p. 114

37 Fig. 7-9b, p. 114

38 7.3-7.5 Key Concepts: Making ATP and NADPH  Photosynthesis proceeds through two stages in the chloroplasts of plants and many types of protists  In the first stage, sunlight energy is converted to the chemical bond energy of ATP  The coenzyme NADPH forms in a pathway that also releases oxygen ( 有 NADPH 有氧,反之則無 )

39 7.6 Light-Independent Reactions: The Sugar Factory  The cyclic, light-independent reactions of the Calvin-Benson cycle are the “synthesis” part of photosynthesis  Calvin-Benson cycle Enzyme-mediated reactions that build sugars in the stroma of chloroplasts

40 Carbon Fixation  Carbon fixation ( 固碳 ) Extraction of carbon atoms from inorganic sources (atmosphere) and incorporating them into an organic molecule Builds glucose from CO 2 Uses bond energy of ATP and the reducing power of NADPH formed in light-dependent reactions

41 The Calvin-Benson Cycle  Enzyme rubisco attaches CO 2 to RuBP Forms two 3-carbon PGA molecules ( 因六碳不穩 定,馬上變成兩個三碳 )  PGAL is formed PGAs receive a phosphate group from ATP, and hydrogen and electrons from NADPH (PGA 吃了這三樣玩意形成 PGAL) Two PGAL combine to form a 6-carbon sugar  Rubisco is regenerated (rubisco 這酶要記一下 )

42 Inputs and Outputs of the Calvin-Benson Cycle

43 The Calvin-Benson Cycle

44 Animation: Calvin-Benson cycle

45 7.7 Adaptations: Different Carbon-Fixing Pathways  Environments differ, and so do details of photosynthesis C3 plants C4 plants CAM plants

46 Stomata  Stomata ( 單數: stoma ,氣孔 ) Small openings through the waxy cuticle covering epidermal surfaces of leaves and green stems Allow CO 2 in and O 2 out Close on dry days to minimize water loss

47 C3 Plants  C3 plants Plants that use only the Calvin–Benson cycle to fix carbon Forms 3-carbon PGA in mesophyll cells ( 葉肉細 胞 ) Used by most plants, but inefficient in dry weather when stomata are closed

48 Photorespiration  When stomata are closed, CO 2 needed for light- independent reactions can’t enter, O 2 produced by light-dependent reactions can’t leave  Photorespiration ( 光呼吸 ) At high O 2 levels, rubisco attaches to oxygen instead of carbon CO 2 is produced rather than fixed 光呼吸成因是 O 2 累積過多,而非 CO 2 無法進來

49 C4 Plants  C4 plants Plants that have an additional set of reactions for sugar production on dry days when stomata are closed; compensates for inefficiency of rubisco Forms 4-carbon oxaloacetate in mesophyll cells, then bundle-sheath cells make sugar Examples: Corn, switchgrass, bamboo

50 C3 and C4 Plant Leaves

51 Animation: C3-C4 comparison

52 CAM Plants  CAM plants (Crassulacean Acid Metabolism) Plants with an alternative carbon-fixing pathway that allows them to conserve water in climates where days are hot Forms 4-carbon oxaloacetate at night, which is later broken down to CO 2 for sugar production Example: succulents, cactuses

53 A CAM Plant  Jade plant (Crassula argentea)

54 C3, C4, and CAM Reactions

55 Fig. 7-13a, p. 117 C3

56 Fig. 7-13b, p. 117 C4

57 Fig. 7-13c, p. 117 CAM

58 7.6-7.7 Key Concepts: Making Sugars  The second stage is the “synthesis” part of photosynthesis, in which sugars are assembled from CO 2  The reactions use ATP and NADPH that form in the first stage of photosynthesis  Details of the reactions vary among organisms

59 7.8 Photosynthesis and the Atmosphere  The evolution of photosynthesis dramatically and permanently changed Earth’s atmosphere

60 Different Food Sources  Autotrophs ( 自營 ) Organisms that make their own food using energy from the environment and inorganic carbon  Heterotrophs ( 異營 ) Organisms that get energy and carbon from organic molecules assembled by other organisms

61 Two Kinds of Autotrophs  Chemoautotrophs ( 化學自營 ) Extract energy and carbon from simple molecules in the environment (hydrogen sulfide, methane) Used before the atmosphere contained oxygen  Photoautotrophs ( 光合自營 ) Use photosynthesis to make food from CO 2 and water, releasing O 2 Allowed oxygen to accumulate in the atmosphere

62 Earth With and Without Oxygen Atmosphere

63 Effects of Atmospheric Oxygen  Selection pressure on evolution of life Oxygen radicals  Development of ATP-forming reactions Aerobic respiration  Formation of ozone (O 3 ) layer Protection from UV radiation

64 7.8 Key Concepts: Evolution and Photosynthesis  The evolution of photosynthesis changed the composition of Earth’s atmosphere  New pathways that detoxified the oxygen by- product of photosynthesis evolved

65 7.9 A Burning Concern  Earth’s natural atmospheric cycle of carbon dioxide is out of balance, mainly as a result of human activity

66 The Carbon Cycle  Photosynthesis locks CO 2 from the atmosphere in organic molecules; aerobic respiration returns CO 2 to the atmosphere A balanced cycle of the biosphere  Humans burn wood and fossil fuels for energy, releasing locked carbon into the atmosphere Contributes to global warming, disrupting biological systems

67 Fossil Fuel Emissions The sky over the Ne York City on a sunny day.

68 7.9 Key Concepts: Photosynthesis, CO 2 & Global Warming  Photosynthesis by autotrophs removes CO 2 from the atmosphere; metabolism by all organisms puts it back in  Human activities have disrupted this balance, and contribute to global warming

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