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You Light up My Life

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You Light up My Life Chapter 7: Photosynthesis Electromagnetic Spectrum Shortest Gamma rays wavelength X-rays UV radiation Visible light Infrared radiation Microwaves Longest Radio waves wavelength Photons • Packets of light energy • Each type of photon has fixed amount of energy • Photons having most energy travel as shortest wavelength (blue-violet light) Visible Light shortest range of most radiation range of heat escaping longest wavelengths reaching Earth’s surface from Earth’s surface wavelengths (most energetic) (lowest energy) gamma x ultraviolet near-infrared infrared microwaves radio rays rays radiation radiation radiation waves VISIBLE LIGHT 400 450 500 550 600 650 700 Wavelengths of light (nanometers) • Wavelengths humans perceive as different colors • Violet (380 nm) to red (750 nm) • Longer wavelengths, lower energy Fig. 7-2, p.108 Pigments • Colors you can see are the wavelengths not absorbed • These light catching particles capture energy from the various wavelengths. Variety of Pigments Chlorophylls a and b Carotenoids - orange Anthocyanins - purple/red Phycobilins - red Xanthophylls - yellow Chlorophylls chlorophyll a chlorophyll b Wavelength absorption (%) absorption Wavelength Wavelength (nanometers) Accessory Pigments Carotenoids, Phycobilins, Anthocyanins beta-carotene phycoerythrin (a phycobilin) percent of wavelengths absorbed wavelengths (nanometers) Pigments Fig. 7-3a, p.109 Pigments Fig. 7-3b, p.109 Pigments Fig. 7-3c, p.109 Pigments Fig. 7-3d, p.109 http://www.youtube.com/watch?v=fwGcOg PB10o&feature=fvsr Fig. 7-3e, p.109 Pigments Fig. 7-3e, p.109 Pigments in Photosynthesis • Bacteria – Pigments in plasma membranes • Plants – Pigments and proteins organized in chloroplast membranes T.E. Englemann’s Experiment Background • Certain bacterial cells will move toward places where oxygen concentration is high • Photosynthesis produces oxygen T.E. Englemann’s Experiment T.E. Englemann’s Experiment Fig. 7-5, p.110 Linked Processes Photosynthesis Aerobic Respiration • Energy-storing pathway • Energy-releasing pathway • Releases oxygen • Requires oxygen • Requires carbon dioxide • Releases carbon dioxide Photosynthesis Equation LIGHT ENERGY 12H2O + 6CO2 6O2 + C2H12O6 + 6H2O Water Carbon Oxygen Glucose Water Dioxide In-text figure Page 111 Chloroplast Structure two outer membranes stroma inner membrane system (thylakoids connected by channels) Fig. 7-6, p.111 Photosynthesis Fig. 7-6a, p.111 Photosynthesis two outer membranes thylakoid compartment thylakoid membrane system inside stroma stroma Fig. 7-6b, p.111 Photosynthesis SUNLIGHT H2O O2 CO2 NADPH, ATP light- light- dependant NADP+, ADP independant reactions reactions sugars CHLOROPLAST Fig. 7-6c, p.111 Where Atoms End Up Reactants 12H2O 6CO2 Products 6O2 C6H12O6 6H2O Two Stages of Photosynthesis sunlight water uptake carbon dioxide uptake ATP LIGHT- ADP + Pi LIGHT- DEPENDENT INDEPENDENT REACTIONS REACTIONS NADPH NADP+ P glucose oxygen release new water Light-Dependent Reactions • Pigments absorb light energy, give up e-, which enter electron transfer chains • Water molecules split, ATP and NADH form, and oxygen is released • Pigments that gave up electrons get replacements LIGHT- HARVESTING COMPLEX PHOTOSYSTEM II sunlight PHOTOSYSTEM I H+ NADPH e- e- e- e- e- e- NADP + + H+ e- H O + + thylakoid 2 H+ H+ H H H+ + H+ H+ + compartment H+ H H O2 H+ thylakoid membrane stroma ADP + Pi ATP cross-section through a disk-shaped fold in the thylakoid membrane H+ Fig. 7-8, p.113 Arrangement of Photosystems water-splitting complex thylakoid compartment H2O 2H + 1/2O2 P680 P700 acceptor acceptor pool of electron PHOTOSYSTEM II carriers stroma PHOTOSYSTEM I Photosystem Function: Harvester Pigments • Most pigments in photosystem are harvester pigments • When excited by light energy, these pigments transfer energy to adjacent pigment molecules • Each transfer involves energy loss Photosystem Function: Reaction Center • Energy is reduced to level that can be captured by molecule of chlorophyll a • This molecule (P700 or P680) is the reaction center of a photosystem • Reaction center accepts energy and donates electron to acceptor molecule Electron Transfer Chain • Adjacent to photosystem Acceptor molecule donates electrons from reaction center • As electrons pass along chain, energy they release is used to produce ATP Pigments in a Photosystem reaction center Cyclic Electron Flow • Electrons – are donated by P700 in photosystem I to acceptor molecule – flow through electron transfer chain and back to P700 • Electron flow drives ATP formation • No NADPH is formed Cyclic Electron Flow e– electron acceptor Electron flow through transfer chain sets up conditions for ATP electron formation at other membrane sites. e– transfer chain e– ATP e– Noncyclic Electron Flow • Two-step pathway for light absorption and electron excitation • Uses two photosystems • Produces ATP and NADPH • Involves photolysis - splitting of water Machinery of Noncyclic Electron Flow H2O second electron photolysis transfer chain e– e– ATP SYNTHASE first electron NADP+ NADPH transfer chain ATP PHOTOSYSTEM II PHOTOSYSTEM I ADP + Pi Energy Changes second transfer chain – e NADPH first e– transfer chain e– e– (Photosystem I) (Photosystem II) + Potential to transfer energy energy (volts) to transfer Potential H2O 1/2O2 + 2H PHOTOSYSTEM I NADPH p700* PHOTOSYSTEM II NADH+ p680* e- photon p700 p680 2H2O Noncyclic Pathway of ATP + 4H + O2 and NADPH Formation Fig. 7-9b, p.114 Chemiosmotic Model of ATP Formation • Electrical and H+ concentration gradients are created between thylakoid compartment and stroma • H+ flows down gradients into stroma through ATP synthesis • Flow of ions drives formation of ATP Chemiosmotic Model for ATP Formation H+ is shunted across Gradients propel H+ Photolysis in the membrane by some through ATP synthases; thylakoid components of ATP forms by compartment splits the first electron phosphate-group water transfer chain transfer H2O – e acceptor ATP SYNTHASE ADP ATP PHOTOSYSTEM II + Pi Light-Independent Reactions • Synthesis part of photosynthesis • Can proceed in the dark • Take place in the stroma • Calvin-Benson cycle Calvin-Benson Cycle • Overall reactants • Overall products – Carbon dioxide – Glucose – ATP – ADP – NADPH – NADP+ 6CO 2 Calvin- ATP Benson 12 PGA 6 RuBP 12 Cycle 6 ADP 12 ADP + Calvin-Benson 12 Pi ATP cycle 12NADPH 4 P i 12 NADP+ 10 PGAL 12 PGAL 1 Pi 1 phosphorylated glucose Fig. 7-10b, p.115 6 CO2 (from the air) CARBON Calvin- Benson FIXATION 6 6 Cycle RuBP unstable intermediate 12 PGA 6 ADP 12 ATP 6 ATP 12NADPH 4 Pi 12 ADP 12 P 10 i 12 NADP+ PGAL 12 PGAL 2 PGAL Pi P glucose Calvin- Benson Cycle THESE REACTIONS PROCEED IN THE CHLOROPLAST’S STROMA Fig. 7-10a, p.115 The C3 Pathway • In Calvin-Benson cycle, the first stable intermediate is a three-carbon PGA • Because the first intermediate has three carbons, the pathway is called the C3 pathway Photorespiration in C3 Plants • On hot, dry days stomata close • Inside leaf – Oxygen levels rise – Carbon dioxide levels drop • Rubisco attaches RuBP to oxygen instead of carbon dioxide • Only one PGAL forms instead of two C3 Plants Fig. 7-11a1, p.116 C3 Plants upper epidermis palisade mesophyll spongy mesophyll lower epidermis stoma leaf vein air space Basswood leaf, cross-section. Fig. 7-11a2, p.116 Stomata closed: CO2 can’t get in; O2 can’t get out C3 Plants Rubisco fixes RuBP 6 PGA + 6 glycolate oxygen, not carbon, in Calvin-Benson mesophyll Cycle cells in leaf 5 PGAL 6 PGAL CO2 + 1 PGAL water Twelve turns of the cycle, not just six, to make one 6-carbon sugar Fig. 7-11a3, p.117 C4 Plants • Carbon dioxide is fixed twice – In mesophyll cells, carbon dioxide is fixed to form four-carbon oxaloacetate – Oxaloacetate is transferred to bundle-sheath cells – Carbon dioxide is released and fixed again in Calvin-Benson cycle C4 Plants Fig. 7-11b1, p.117 C4 Plants upper epidermis mesophyll cell bundle- sheath cell lower epidermis Basswood leaf, cross-section. Stomata closed: CO2 can’t get in; O2 can’t get out Carbon fixed in the mesophyll cell, malate PEP oxaloacetate diffuses into adjacent bundle- C4 sheath cell cycle malate C4 pyruvate Plants CO2 In bundle-sheath cell, malate gets converted to RuBP Calvin- 12 PGAL pyruvate with Benson release of CO2, Cycle which enters Calvin-Benson 10 PGAL 12 PGAL cycle 2 PGAL 1 sugar Fig. 7-11b3, p.117 CAM Plants • Carbon is fixed twice (in same cells) • Night – Carbon dioxide is fixed to form organic acids • Day – Carbon dioxide is released and fixed in Calvin- Benson cycle CAM Plants Fig. 7-11c1, p.117 stoma epidermis with thick cuticle mesophyll cell air space CAM Plants Fig. 7-11c2, p.117 Stomata stay closed during day, CAM Plants open for CO2 uptake at night only. C4 cycle operates at night when CO2 from aerobic C4 respiration fixed CYCLE CO2 that accumulated overnight used in C3 cycle during the day Calvin- Benson Cycle 1 sugar Fig. 7-11c3, p.117 Summary of Photosynthesis light LIGHT-DEPENDENT REACTIONS 6O2 12H2O + ADP + Pi ATP NADP NADPH LIGHT-INDEPENDENT REACTIONS PGA CALVIN- PGAL BENSON 6H O 6CO2 CYCLE 2 RuBP P C6H12O6 (phosphorylated glucose) end product (e.g., sucrose, starch, cellulose) Figure 7-14 Page 120 Photoautotrophs • Capture sunlight energy and use it to carry out photosynthesis – Plants – Some bacteria – Many protistans Photoautotrophs Winter NORTH SPAIN AMERICA ATLANTIC OCEAN AFRICA Spring Fig. 7-13, p.119 Satellite Images Show Photosynthesis Atlantic Ocean Photosynthetic activity in spring Figure 7-13 Page 119 sunlight Light- Dependent 12H2O 6O2 Reactions ATP + ADP + Pi NADPH NADP 6CO2 Calvin- 6 RuBP Benson 12 PGAL cycle Light- 6H O Independent 2 Reactions phosphorylated glucose end products (e.g., sucrose, starch, cellulose) Fig. 7-14, p.120 Fig. 7-15, p.121 Fig. 7-16a, p.121 Fig. 7-16b, p.121.
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