Overview The process that feeds the biosphere 1

Overview: The process that feeds the biosphere 1. Photosynthesis光合作用 : the process that converts solar energy into chemical energy 2. Plants and other autotrophs自營are the producers of the biosphere 3. Plants are photoautotrophs光合自營they use the energy of sunlight to make organic molecules from water and carbon dioxide Other organisms also benefit from photosynthesis. 2

Figure 10. 2 4. Photosynthesis occurs in plants, algae, certain other protists原生生物 and some prokaryotes原核生物 5. Heterotrophs異營obtain their organic material from other organisms are the consumers消費者of the biosphere (a) Plants (b) Multicellular alga (d) Cyanobacteria (c) Unicellular protists 40 m 10 m (e) Purple sulfur 1 m bacteria 3

10. 1 Photosynthesis converts light energy to the chemical energy of food A. Chloroplasts葉綠體: The sites of photosynthesis in plants Mesophyll Stomata 1. The leaves of plants are the major sites of photosynthesis 2. Chloroplasts are the organelles in which photosynthesis occurs, contain thylakoids類囊體 and grana葉綠層 Leaf cross section Chloroplasts Vein Chloroplast Thylakoid Stroma Granum space 1 μm CO 2 Mesophyll cell Outer membrane Intermembrane space Inner membrane 20 μm 4

3. Chloroplasts are divided into three functional compartments by a system of membranes: Chloroplast i. Intermembrane space ii. Thylakoid space iii. stroma(基質) Outer membrane Stroma Thylakoid Granum Thylakoid space Intermembrane space Inner membrane 1 m 5

Tracking atoms through photosynthesis: Scientific inquiry Photosynthesis is summarized as: 6 CO 2 + 12 H 2 O+ Light —> C 2 H 12 O 6 + 6 O 2 + 6 H 2 O energy 1. The splitting of water: Chloroplasts split water into hydrogen and oxygen, incorporating the electrons of hydrogen into sugar molecules 2. Photosynthesis as a redox process: Water is oxidized, carbon dioxide is reduced Reactants: Products: 6 CO 2 C 6 H 12 O 6 12 H 2 O 6 O 2 6

C. The two stages of photosynthesis: A preview 1. Photosynthesis consists of two processes: light reactions光反應and the Calvin cycle卡爾文循環 2. The light reactions: occur in the grana, split water, release oxygen, produce ATP, and form NADPH. The light reactions power the addition of a phosphate group to ADP in a process called photophosphorylation光合磷酸化 3. The Calvin cycle: occurs in the stroma forms sugar from carbon dioxide, using ATP for energy and NADPH for reducing power Light H 2 O CO 2 NADP+ LIGHT REACTIONS ADP Pi CALVIN CYCLE ATP Thylakoid Stroma NADPH Chloroplast O 2 [CH 2 O] (sugar) 7

10. 2: The light reactions convert solar energy太陽能 to the chemical energy of ATP and NADPH A. The Nature of Sunlight 1. Light: a form of electromagnetic energy電磁能, which travels in waves波 2. Wavelength: is the distance between the crests of waves and determines the type of electromagnetic energy 3. Electromagnetic spectrum 電磁光譜: the entire range of electromagnetic energy, or radiation輻射 4. Visible light spectrum可見光譜: includes the colors of light we can see and includes the wavelengths that drive photosynthesis 10− 5 nm 10− 3 Gamma rays nm 1 nm X-rays 10 UV 3 nm 10 Infrared 6 nm 1 m (10 9 nm) Microwaves 10 3 m Radio waves Visible light 380 450 Shorter wavelength Higher energy 500 550 600 650 700 750 nm Longer wavelength Lower energy 8

B. Photosynthetic pigments色素: The light receptors受體 or 受器 Pigments: are substances that absorb visible light, reflect light, which include the colors we see Light Reflected light Chloroplast Absorbed light Granum Transmitted light 9

Determining of an absorption spectrum Spectrophotometer光電比色計: is a machine that sends light through pigments and measures the fraction of light transmitted at each wavelength Refracting prism White light Chlorophyll solution 2 1 Slit moves to pass light of selected wavelength. Photoelectric tube Galvanometer 3 4 Green light Blue light 10

3. The action spectrum 作用光譜: is a pigment profiles the relative effectiveness of different wavelengths of radiation in driving photosynthesis Absorption of light by chloroplast pigments 2. The absorption spectra of chloroplast pigments provide clues to the relative effectiveness of different wavelengths for driving photosynthesis Rate of photosynthesis (measured by O 2 release) 1. Absorption spectrum吸收光譜: is a graph plotting light absorption versus wavelength Chlorophyll a Chlorophyll b Carotenoids 400 500 600 700 Wavelength of light (nm) 400 500 600 700 Aerobic bacteria Filament of alga 4. The action spectrum for photosynthesis was first demonstrated by Theodor W. Engelmann 400 500 Which wavelengths of light are most effective in driving photosynthesis? 600 700 11

5. The absorption spectra of three types of pigments in chloroplasts i. Chlorophyll a: the main photosynthetic pigment ii. Chlorophyll b: is an accessory pigment iii. Other accessory pigments: absorb different wavelengths of light and pass the energy to chlorophyll a, ex. Carotenoids類葫蘿蔔素 have phtotprotection function 12

Excitation 激發of chlorophyll by light 1. When a pigment absorbs light it goes from a ground state 基態to an excited state激態, which is unstable 2. If an isolated solution of chlorophyll is illuminated it will fluoresce發螢光, giving off light and heat Energy of electron e Excited state Heat Photon (fluorescence) Photon Chlorophyll molecule Ground state (a) Excitation of isolated chlorophyll molecule (b) Fluorescence 13

A Photosystem光系統: A reaction Center complex作用中心複合體associated with light-harvesting complexes 1. A photosystem is composed of a reaction-center complex surrounded by a number of light-harvesting complexes. 2. The light-harvesting complexes consist of pigment molecules bound to particular proteins and funnel the energy of photons光子 of light to the reaction center 3. When a reaction-center chlorophyll molecule absorbs energy one of its electrons gets bumped up to a primary electron acceptor 14

Thylakoid membrane Chlorophyll Protein subunits STROMA THYLAKOID SPACE (b) Structure of photosystem II 15

§ 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 (so called P 680) § Photosystem I (PS I) is best at absorbing a wavelength of 700 nm (so called P 700) © 2014 Pearson Education, Inc.

The thylakoid membrane is populated by two types of photosystems I (PSI-p 700) and II (PS II -p 680) A. Linear Electron Flow 線性電子流 Ele ct Primary acceptor 1/ 2 H 2 + O 2 H 2 O e 2 ron Pq 4 tran Primary acceptor spo rt c hai n e Cytochrome complex 3 E tra lect ch ns ron ai po n rt 7 Fd e e 8 NADP reductase Pc e e NADP + H NADPH P 700 5 P 680 Light 1 Light 6 ATP Pigment molecules Photosystem II (PS II) Photosystem I (PS I) Pq: plastoquinone Pc: plastocyanin Fd: ferredoxin 17

Linear Electron Flow 1. Noncyclic electron flow: the primary pathway of energy transformation in the light reactions produces NADPH, ATP, and oxygen. 2. A mechanical analogy for the light reactions 18

Cyclic Electron Flow循環電子流 1. Under certain conditions, photoexcited electrons take an alternative path 2. In cyclic electron flow only photosystem I is used, only ATP is produced Primary acceptor Fd Fd Pq NADP reductase Cytochrome complex NADP H NADPH Pc Photosystem II ATP Summary of light reactions: 1. During noncyclic electron flow, the photosystems of the thylakoid membrane transform light energy to the chemical energy stored in NADPH and ATP. 2. During cyclic electron flow, electrons ejected from P 700 reach ferredoxin and flow back to P 700, Produces ATP but doesn’t produce NADPH or O 2. 19

Comparison of chemiosmosis in chloroplasts and mitochondria Chloroplast Mitochondrion 1. Generate ATP by the same basic mechanism: chemiosmosis 2. Use different sources of energy to accomplish this: light and chemical energy 3. Different spatial organization 空間結構of chemiosmosis CHLOROPLAST STRUCTURE MITOCHONDRION STRUCTURE 4. In both organelles 胞器redox reactions of electron transport chains generate a H+ gradient across a membrane H Intermembrane space Inner membrane 5. ATP synthase ATP合成酶 : uses this proton-motive force to make ATP Diffusion Electron transport chain Thylakoid space Thylakoid membrane ATP synthase Matrix Stroma ADP P i Key Higher [H ] H ATP Lower [H ] 20

The light reactions and chemiosmosis: the organization of the thylakoid membrane There are three steps in the light reactions that contribute to the proton gradient across the thylakoid membrane: 1. Water is split by Photosystem II on the thylakoid side, releasing protons in the process. 2. As plastoquinone (Pq), a mobile carrier, transfers electrons to the cytochrome 細胞色素complex, it translocates protons from the stroma to the thylakoid space. 3. Protons in the stroma are removed from solution as NADP＋ is reduced to NADPH. ATP and NADPH are produced on the side facing the stroma, where the Calvin cycle takes place In summary, light reactions generate ATP and increase the potential energy of electrons by moving them from H 2 O to NADPH 21

STROMA (low H concentration) Cytochrome complex Photosystem II Light 4 H+ Light NADP reductase 3 Fd Pq H 2 O THYLAKOID SPACE (high H concentration) 1/ 2 Pc O 2 +2 H+ 4 H+ To Calvin Cycle Thylakoid membrane STROMA (low H concentration) NADPH 2 1 NADP + H ATP synthase ADP + Pi ATP H+ 22

Concept 10. 3: The Calvin cycle uses the chemical energy of ATP and NADPH to reduce CO 2 to sugar § The cycle builds sugar from smaller molecules by using ATP and the reducing power of electrons carried by NADPH § Carbon enters the cycle as CO 2 and leaves as a sugar named glyceraldehyde 3 -phospate (G 3 P) § For net synthesis of 1 G 3 P, the cycle must take place three times, fixing 3 molecules of CO 2 § The Calvin cycle has three phases 1. Carbon fixation (catalyzed by rubisco) 2. Reduction 3. Regeneration of the CO 2 acceptor (Ru. BP) © 2014 Pearson Education, Inc.

Figure 10. UN 03 H 2 O CO 2 Light NADP CALVIN LIGHT CYCLE

10. 3 The Calvin cycle uses ATP and NADPH to convert CO 2 to sugar The Calvin cycle: similar to the citric acid cycle, occurs in the stroma Input 3 (Entering one CO 2 at a time) Phase 1: Carbon fixation Rubisco 3 P Short-lived intermediate P 6 P 3 -Phosphoglycerate P 3 P Ribulose bisphosphate (Ru. BP) 6 ATP 6 ADP 3 ADP Calvin Cycle 3 ATP 6 P P 1, 3 -Bisphoglycerate 6 NADPH Phase 3: Regeneration of the CO 2 acceptor (Ru. BP) 5 6 NADP 6 Pi P G 3 P 6 P Glyceraldehyde 3 -phosphate (G 3 P) 1 G 3 P (a sugar) Output P Glucose and other organic compounds Phase 2: Reduction 25

1. The Calvin cycle has three phases a. Carbon fixation 碳固定: each molecule of CO 2 is attached to a five-carbon sugar, ribulose biphosphate (Ru. BP) by an enzyme Ru. BP carboxlase (rubisco). Input 3 CO 2 (Entering one at a time) Phase 1: Carbon fixation Rubisco 3 P Short-lived intermediate P 3 P Ribulose bisphosphate (Ru. BP) P 6 P 3 -Phosphoglycerate 26

b. Reduction: a two-step process that couples ATP hydrolysis with the reduction of 3 -phosphoglycerate to glyceraldehydes phosphate. Input 3 (Entering one CO 2 at a time) Phase 1: Carbon fixation Rubisco 3 P Short-lived intermediate P 6 P 3 -Phosphoglycerate P 3 P Ribulose bisphosphate (Ru. BP) 6 ATP 6 ADP Calvin Cycle 6 P P 1, 3 -Bisphoglycerate 6 NADPH 6 NADP 6 Pi 6 P Glyceraldehyde 3 -phosphate (G 3 P) 1 G 3 P (a sugar) Output Phase 2: Reduction P Glucose and other organic compounds 27

c. Regeneration of the CO 2 acceptor (Ru. BP): A complex series of reactions rearranges the carbon skeletons of five G 3 P molecules into three Input Ru. BP molecules 3 (Entering one CO 2 at a time) Phase 1: Carbon fixation Rubisco 3 P Short-lived intermediate P 6 P 3 -Phosphoglycerate P 3 P Ribulose bisphosphate (Ru. BP) 6 ATP 6 ADP 3 Calvin Cycle 6 P P 1, 3 -Bisphoglycerate ATP Phase 3: Regeneration of the CO 2 acceptor 5 (Ru. BP) 6 NADPH 6 NADP 6 Pi P G 3 P 6 P Glyceraldehyde 3 -phosphate (G 3 P) 1 G 3 P (a sugar) Output P Glucose and other organic compounds Phase 2: Reduction 28

The Calvin cycle a. For the net synthesis of one G 3 P molecule, the Calvin cycle uses the products of the light reactions: 9 ATP molecules and 6 NADPH molecules. b. G 3 P produced by the Calvin cycle is the raw material used to synthesize glucose and other carbohydrates. c. The Calvin cycle uses 18 ATP and 12 NADPH molecules to produce one glucose molecule 29

10. 4 Alternative mechanisms of carbon fixation have evolved in hot, arid climates A. Photorespiration in a C 3 plant 光呼吸作用目的? ? ? Soybeans Wheat Rice Oats 30

On hot dry days, C 3 plants close their stomata 氣孔to conserving water but limiting access to CO 2 and causing oxygen to build up A. Photorespiration 光呼吸: An evolutionary relic? Photorespiration: O 2 substitutes for CO 2 in the active site of the enzyme rubisco and the photosynthetic rate is reduced Rubisco transfer O 2 to Ru. Bp Resulting 5 -C molecular splits into Two-C molecular（glycolate甘醇酸 ) （3 -phosphoglycolate） Leaves chloroplast & goes to peroxisome Three-C molecule Stays in the Calvin cycle A metabolic pathway begin in the peroxisome and is completed in the mitochondria Glycolate is broken down into CO 2 31

B. C 4 Plants 1. C 4 plants minimize the cost of photorespiration by incorporating CO 2 into four carbon compounds in mesophyll cells葉肉 2. These four carbon compounds are exported to bundle sheath cells束鞘細胞, where they release CO 2 used in the Calvin cycle 3. C 4 leaf anatomy and the C 4 pathway The C 4 pathway C 4 leaf anatomy Photosynthetic cells of C 4 plant leaf Mesophyll cell PEP carboxylase CO 2 Oxaloacetate (4 C) PEP (3 C) ADP Bundlesheath cell Malate (4 C) Bundlesheath cell Vein (vascular tissue) ATP Pyruvate (3 C) CO 2 Calvin Cycle Sugar Stoma Vascular tissue 32

C. CAM Plants 1. CAM ( crassulacean acid 景天酸metabolism) plants: open their stomata at night, incorporating CO 2 into organic acids 2. During the day, the stomata close and the CO 2 is released from the organic acids for use in the Calvin cycle CAM 1 CO 2 incorporated (carbon fixation) CO 2 Organic acid Night CO 2 2 CO 2 released to the Calvin cycle Calvin Cycle Day Sugar (b) Temporal separation of steps 33

3. The CAM pathway is similar to the C 4 pathway 1. Differ in that the initial steps of carbon fixation in C 4 plants are structurally separate from the Calvin cycle; in CAM plants, the two steps occur at separate times. 2. Regardless of whether the plant uses a. C 3, C 4 or CAM pathway, all plants use the Calvin cycle to produce sugar from CO 2. Sugarcane Pineapple C 4 CAM CO 2 Mesophyll Organic acid cell 1 CO 2 incorporated (carbon fixation) Organic acid Calvin Cycle Sugar (a) Spatial separation of steps Night CO 2 Bundlesheath cell CO 2 2 CO 2 released to the Calvin cycle Calvin Cycle Day Sugar (b) Temporal separation of steps 34

The Importance of Photosynthesis: A Review § The energy entering chloroplasts as sunlight gets stored as chemical energy in organic compounds § Sugar made in the chloroplasts supplies chemical energy and carbon skeletons to synthesize the organic molecules of cells § Plants store excess sugar as starch in structures such as roots, tubers, seeds, and fruits § In addition to food production, photosynthesis produces the O 2 in our atmosphere © 2014 Pearson Education, Inc.

Figure 10. 22 a O 2 CO 2 H 2 O Sucrose (export) Mesophyll cell H 2 O Chloroplast CO 2 Light NADP LIGHT REACTIONS: Photosystem II Electron transport chain Photosystem I Electron transport chain H 2 O © 2014 Pearson Education, Inc. O 2 ADP Pi ATP NADPH 3 -Phosphoglycerate Ru. BP CALVIN CYCLE G 3 P Starch (storage) Sucrose (export)

Figure 10. 22 b LIGHT REACTIONS • Are carried out by molecules in the thylakoid membranes • Convert light energy to the chemical energy of ATP and NADPH • Split H 2 O and release O 2 to the atmosphere © 2014 Pearson Education, Inc. CALVIN CYCLE REACTIONS • Take place in the stroma • Use ATP and NADPH to convert CO 2 to the sugar G 3 P • Return ADP, inorganic phosphate, and NADP to the light reactions

Global warming and deforestation 全球暖化及去森林化: Excess CO 2 in the atmosphere is contributing to global warming, photosynthesis, which removes CO 2 from the atmosphere moderates this warming The increase in atmospheric carbon dioxide at Mauna Loa, Hawaii, and average global temperatures over land from 1958 to 2004 38

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You should now be able to: l Describe the structure of a chloroplast l Describe the relationship between an action spectrum and an absorption spectrum l Trace the movement of electrons in linear electron flow l Trace the movement of electrons in cyclic electron flow l Describe the similarities and differences between oxidative phosphorylation in mitochondria and photophosphorylation in chloroplasts l Describe the role of ATP and NADPH in the Calvin cycle l Describe the major consequences of photorespiration l Describe two important photosynthetic adaptations that minimize photorespiration 40