photosynthesis

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© 2011 Pearson Education, Inc. converts solar energy into chemical energy that feeds the world Photosynthesis is the Process That Feeds the Biosphere……..

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Autotrophs - the producers of the biosphere, producing organic molecules from CO 2 and other inorganic molecules Photosynthetic organisms are photoautotrophs , using the energy of sunlight and CO 2 to make organic molecules © 2011 Pearson Education, Inc.

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Heterotrophs obtain their organic material from other organisms the consumers of the biosphere depend on photoautotrophs for food and O 2 © 2011 Pearson Education, Inc.

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Plants algae Unicellular protists Cyanobacteria Purple sulfur bacteria Figure 10.2 PSS occurs in plants, algae, certain protists, and some prokaryotes These organisms feed not only themselves but also most of the living world

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Mesophyll Chloroplasts Vein Stomata Chloroplast Mesophyll cell CO 2 O 2 Leaves get green color from chlorophyl l – (green pigment within chloroplasts) Chloroplasts found mainly in mesophyll tissue cells of leaf

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Outer membrane Inner membrane Thylakoid Granum Stroma Chloroplast Figure 10.4b Chloroplasts – organelles that perform photosynthesis

Photosynthesis is the Process That Feeds the Biosphere……..:

6 CO 2 + 12 H 2 O + Light energy  C 6 H 12 O 6 + 6 O 2 + 6 H 2 O © 2011 Pearson Education, Inc. PSS is an endergonic process ……. the energy is provided by sun light Photosynthesis converts light energy into chemical energy (food) Carbon dioxide water sunlight glucose oxygen water + + + + 

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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 - Chloroplasts split H 2 O into H and O - incorporate the electrons of H into sugar molecules - and release O 2 as a by-product

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Figure 10.UN01 Energy  6 CO 2  6 H 2 O C 6 H 12 O 6  6 O 2 becomes reduced becomes oxidized H 2 O is oxidized and CO 2 is reduced Photosynthesis as a Redox Process

Figure 10.2:

Thylakoids Chloroplast 1 st - Light reactions ( photo ) and 2 nd - Calvin cycle ( synthesis ) The light reactions (in the thylakoids)………… Split H 2 O Release O 2 Reduce NADP + to NADPH Generate ATP from ADP by photophosphorylation 2 Stages of Photosynthesis:

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Stroma Chloroplast 2 Stages of Photosynthesis: 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

Figure 10.4b:

Light Light Reactions Chloroplast ATP NADPH NADP  ADP + P i H 2 O O 2 Figure 10.6-2 Light reactions in thylakoids

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Light Calvin Cycle Chloroplast [CH 2 O] (sugar) ATP NADPH NADP  ADP + P i H 2 O CO 2 O 2 Calvin Cycle in the Stroma

Figure 10.5:

Gamma rays X-rays UV Infrared Micro- waves Radio waves Visible light Lower energy Higher energy 380 450 500 550 600 650 700 750 nm 10  5 nm 10  3 nm 1 nm 10 3 nm 10 6 nm (10 9 nm) 10 3 m 1 m wavelengths that produce colors we can see Electromagnetic Spectrum – entire range of electromagnetic energy Photons = Light behaves like discrete particles Light is electromagnetic energy - it travels in rhythmic waves

Figure 10.UN01:

Photosynthetic Pigments: The Light Receptors Pigments - absorb visible light Different pigments absorb different wavelengths Wavelengths that are not absorbed are reflected or transmitted Photosynthetic organisms use pigments to capture different wavelengths of light © 2011 Pearson Education, Inc.

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Chloroplast Light Reflected light Absorbed light Transmitted light Granum Leaves appear green because chlorophyll reflects and transmits green light

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Bacterium Wavelength of light (nm) 400 500 600 700 Light # O 2 using bacteria Algal cells Prism Microscope slide absorption spectrum of chlorophyll a  violet-blue and red light work best for PSS

Figure 10.6-2:

Chlorophyll solution Galvanometer pass light of selected wavelength. Green light High transmittance (low absorption): Chlorophyll absorbs very little green light. Blue light Low transmittance (high absorption): Chlorophyll absorbs most blue light. spectrophotometer - measures a pigment’s ability to absorb diff wavelengths (measures the fraction of light transmitted at each wavelength)

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Action spectrum Absorption spectrum Chloro- phyll a Chlorophyll b Carotenoids Wavelength of light (nm) Absorption of light by chloroplast pigments Rate of photosynthesis (measured by O 2 release) 400 500 600 700 400 500 600 700 400 500 600 700 plots a pigment’s light absorption versus wavelength relative effectiveness of diff wavelengths in driving a process

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© 2011 Pearson Education, Inc. Chlorophyll a the primary photosynthetic pigment chlorophyll b (accessory pigment) broaden the spectrum used for photosynthesis carotenoids (accessory pigment) absorb excessive light that would damage chlorophyll Carotenoids and xanthophils also accessory pigments that can absorb other wavelengths of light in fall, when earth tilts and wavelengths change Photosynthetic Pigments: The Light Receptors

Photosynthetic Pigments: The Light Receptors:

Figure 10.12 Excited state Heat e  Photon (fluorescence) Ground state Photon Chlorophyll Energy of electron Excitation of chlorophyll molecule by light

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Photosystems = harvest 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 (INTERIOR OF THYLAKOID) e  light-harvesting complexes - (pigment molecules bound to proteins) that transfer the energy of photons to the reaction center

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© 2011 Pearson Education, Inc. Photosystem II (PS II) (actually functions first) - is best at absorbing a wavelength of 680 nm The reaction-center chlorophyll a of PS II is called P680 Photosystem I (PS I) - is best at absorbing a wavelength of 700 nm The reaction-center chlorophyll a of PS I is called P700 2 types of Photosystems in the thylakoid membrane that participate in Light Reactions

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Primary acceptor P680 Light Pigment molecules Photosystem II (PS II ) 1 2 e  photon hits a pigment and its energy is passed among pigment molecules until it excites P680 excited electron from P680 is transferred to the primary electron acceptor (now called P680 + )

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Figure 10.14-2 Primary acceptor H 2 O O 2 2 H  + 1 / 2 P680 Light Pigment molecules Photosystem II (PS II ) 1 2 3 e  e  e  H 2 O is split by enzymes electrons are transferred from the H atoms to P680 + (reducing it to P680) O 2 is released as a by-product

Photosynthetic Pigments: The Light Receptors:

Cytochrome complex Primary acceptor H 2 O O 2 2 H  + 1 / 2 P680 Light Pigment molecules Photosystem II (PS II ) Pq Pc ATP 1 2 3 5 Electron transport chain e  e  e  4 electrons “fall” down an electron transport chain from PS II to PS I Energy released builds a proton gradient across the thylakoid membrane Diffusion of H + across the membrane drives ATP synthesis

Figure 10.12:

MITOCHONDRION STRUCTURE CHLOROPLAST STRUCTURE Intermembrane space Inner membrane Matrix Thylakoid space Thylakoid membrane Stroma Electron transport chain H  Diffusion ATP synthase H  ADP  P i Key Higher [H  ] Lower [H  ] ATP Mitochondria and Chloroplasts generate ATP by chemiosmosis

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Cytochrome complex Primary acceptor Primary acceptor H 2 O O 2 2 H  + 1 / 2 P680 Light Pigment molecules Photosystem II (PS II ) Photosystem I (PS I ) Pq Pc ATP 1 2 3 5 6 Electron transport chain P700 Light e  e  4 e  e  PS I light energy excites P700, and loses an electron to an electron acceptor P700 + (P700 minus an electron) accepts an electron from PS II via the ETC

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Figure 10.14-5 Cytochrome complex Primary acceptor Primary acceptor H 2 O O 2 2 H  + 1 / 2 P680 Light Pigment molecules Photosystem II (PS II ) Photosystem I (PS I ) Pq Pc ATP 1 2 3 5 6 7 8 Electron transport chain Electron transport chain P700 Light + H  NADP  NADPH NADP  reductase Fd e  e  e  e  4 e  e  Each electron from the primary electron acceptor of PS I goes to ferredoxin ( Fd ) electrons are transferred to NADP + and reduce it to NADPH electrons of NADPH are available for the reactions of the Calvin cycle This process also removes a H + from the stroma

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STROMA (low H  concentration) 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 1 3 NADPH Fd Pc Pq 4 H + 4 H + +2 H + H + ADP + P i ATP 1 / 2 H 2 O O 2 Light Reactions - ATP and NADPH are produced on the side facing the stroma , (where the Calvin cycle takes place) The Calvin cycle builds sugar from CO 2 by using ATP and the reducing power of electrons carried by NADPH

Figure 10.14-2:

The Calvin cycle - reduces CO 2 to sugar © 2011 Pearson Education, Inc. The Calvin cycle has three phases……………. Carbon fixation (catalyzed by rubisco ) Reduction Regeneration of (the CO 2 acceptor) RuBP

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Input 3 (Entering one at a time) CO 2 Phase 1: Carbon fixation Rubisco 3 P P P 6 Short-lived intermediate 3-Phosphoglycerate 3 P P Ribulose bisphosphate (RuBP) Figure 10.19-1 Carbon enters the cycle as CO 2 CALVIN CYCLE

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Input 3 (Entering one at a time) CO 2 Phase 1: Carbon fixation Rubisco 3 P P P 6 Short-lived intermediate 3-Phosphoglycerate 6 6 ADP ATP 6 P P 1,3-Bisphosphoglycerate Calvin Cycle 6 NADPH 6 NADP  6 P i 6 P Phase 2: Reduction Glyceraldehyde 3-phosphate (G3P) 3 P P Ribulose bisphosphate (RuBP) 1 P G3P (a sugar) Output Glucose and other organic compounds Figure 10.19-2 carbon leaves as a sugar G3P (glyceraldehyde 3-phospate)

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Input 3 (Entering one at a time) CO 2 Phase 1: Carbon fixation Rubisco 3 P P P 6 Short-lived intermediate 3-Phosphoglycerate 6 6 ADP ATP 6 P P 1,3-Bisphosphoglycerate Calvin Cycle 6 NADPH 6 NADP  6 P i 6 P Phase 2: Reduction Glyceraldehyde 3-phosphate (G3P) P 5 G3P ATP 3 ADP Phase 3: Regeneration of the CO 2 acceptor (RuBP) 3 P P Ribulose bisphosphate (RuBP) 1 P G3P (a sugar) Output Glucose and other organic compounds 3 the cycle must turn 3 times (fix 3 molecules of CO 2 ) to net 1 G3P

Figure 10.14-5:

Light Light Reactions: Photosystem II Electron transport chain Photosystem I Electron transport chain NADP  ADP + P i RuBP ATP NADPH 3-Phosphoglycerate Calvin Cycle G3P Starch (storage) Sucrose (export) Chloroplast H 2 O CO 2 O 2 Figure 10.22

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Alternative mechanisms of carbon fixation in hot, arid climates On hot, dry days plants close stomata to conserve H 2 O but this also limits photosynthesis…….. reduces access to CO 2 and causes O 2 to build up These conditions favor the apparently wasteful process of photorespiration © 2011 Pearson Education, Inc. In photorespiration - rubisco fixes 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

The Calvin cycle - reduces CO2 to sugar:

The C 4 pathway 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 enzyme PEP carboxylase incorporates CO 2 into 4-C compounds 4-C compounds are exported to bundle-sheath cells , where they release CO 2 that is then used in the Calvin cycle

Figure 10.19-1:

CAM Plants Cacti & succulents use crassulacean acid metabolism (CAM) to fix carbon open stomata at night, incorporating CO 2 into organic acids Stomata close during day – CO 2 is released from organic acids and used in the Calvin cycle © 2011 Pearson Education, Inc.

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