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BioLogy-Photosynthesis-chapterr10ppt.ppt

1. Photosynthesis is the process by which plants, algae, and some bacteria use sunlight, water and carbon dioxide to produce oxygen and energy in the form of ATP and NADPH. 2. It occurs in two stages - the light-dependent reactions where solar energy is captured to make ATP and NADPH, and the light-independent Calvin cycle where carbon is incorporated into organic compounds using ATP and NADPH. 3. The light reactions take place in the thylakoid membranes of chloroplasts and utilize two photosystems, photosystem II and photosystem I, to transfer electrons down an electron transport chain and pump protons across the membrane, driving ATP synthesis.

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LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson © 2011 Pearson Education, Inc. Lectures by Erin Barley Kathleen Fitzpatrick Photosynthesis Chapter 10
Overview: The Process That Feeds the Biosphere • Photosynthesis is the process that converts solar energy into chemical energy • Directly or indirectly, photosynthesis nourishes almost the entire living world © 2011 Pearson Education, Inc.
• Autotrophs sustain themselves without eating anything derived from other organisms • Autotrophs are the producers of the biosphere, producing organic molecules from CO2 and other inorganic molecules • Almost all plants are photoautotrophs, using the energy of sunlight to make organic molecules © 2011 Pearson Education, Inc.
Figure 10.1
• Photosynthesis occurs in plants, algae, certain other protists, and some prokaryotes • These organisms feed not only themselves but also most of the living world © 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc. BioFlix: Photosynthesis
(a) Plants (b) Multicellular alga (c) Unicellular protists (d) Cyanobacteria (e) Purple sulfur bacteria 10 m 1 m 40 m Figure 10.2
• 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 O2 © 2011 Pearson Education, Inc.
• 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 © 2011 Pearson Education, Inc.
Figure 10.3
Concept 10.1: 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 © 2011 Pearson Education, Inc.
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 © 2011 Pearson Education, Inc.
• CO2 enters and O2 exits the leaf through microscopic pores called stomata • The chlorophyll is in the membranes of thylakoids (connected sacs in the chloroplast); thylakoids may be stacked in columns called grana • Chloroplasts also contain stroma, a dense interior fluid © 2011 Pearson Education, Inc.
Figure 10.4 Mesophyll Leaf cross section Chloroplasts Vein Stomata Chloroplast Mesophyll cell CO2 O2 20 m Outer membrane Intermembrane space Inner membrane 1 m Thylakoid space Thylakoid Granum Stroma
Mesophyll Leaf cross section Chloroplasts Vein Stomata Chloroplast Mesophyll cell CO2 O2 20 m Figure 10.4a
Outer membrane Intermembrane space Inner membrane 1 m Thylakoid space Thylakoid Granum Stroma Chloroplast Figure 10.4b
Tracking Atoms Through Photosynthesis: Scientific Inquiry • Photosynthesis is a complex series of reactions that can be summarized as the following equation: 6 CO2 + 12 H2O + Light energy  C6H12O6 + 6 O2 + 6 H2O © 2011 Pearson Education, Inc.
The Splitting of Water • Chloroplasts split H2O into hydrogen and oxygen, incorporating the electrons of hydrogen into sugar molecules and releasing oxygen as a by-product © 2011 Pearson Education, Inc.
Figure 10.5 Reactants: Products: 6 CO2 6 H2O 6 O2 12 H2O C6H12O6
Photosynthesis as a Redox Process • Photosynthesis reverses the direction of electron flow compared to respiration • Photosynthesis is a redox process in which H2O is oxidized and CO2 is reduced • Photosynthesis is an endergonic process; the energy boost is provided by light © 2011 Pearson Education, Inc.
Figure 10.UN01 Energy  6 CO2  6 H2O C6 H12 O6  6 O2 becomes reduced becomes oxidized
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 H2O – Release O2 – Reduce NADP+ to NADPH – Generate ATP from ADP by photophosphorylation © 2011 Pearson Education, Inc.
• The Calvin cycle (in the stroma) forms sugar from CO2, using ATP and NADPH • The Calvin cycle begins with carbon fixation, incorporating CO2 into organic molecules © 2011 Pearson Education, Inc.
Light Light Reactions Chloroplast ATP NADPH NADP ADP + P i H2O O2 Figure 10.6-2
Light Light Reactions Calvin Cycle Chloroplast [CH2O] (sugar) ATP NADPH NADP ADP + P i H2O CO2 O2 Figure 10.6-4
Concept 10.2: The light reactions convert solar energy to the chemical energy of ATP and NADPH • Chloroplasts are solar-powered chemical factories • Their thylakoids transform light energy into the chemical energy of ATP and NADPH © 2011 Pearson Education, Inc.
The Nature of Sunlight • Light is a form of electromagnetic energy, also called electromagnetic radiation • Like other electromagnetic energy, light travels in rhythmic waves • Wavelength is the distance between crests of waves • Wavelength determines the type of electromagnetic energy © 2011 Pearson Education, Inc.
• The electromagnetic spectrum is the entire range of electromagnetic energy, or radiation • Visible light consists of wavelengths (including those that drive photosynthesis) that produce colors we can see • Light also behaves as though it consists of discrete particles, called photons © 2011 Pearson Education, Inc.
Figure 10.7 Gamma rays X-rays UV Infrared Micro- waves Radio waves Visible light Shorter wavelength Longer wavelength Lower energy Higher energy 380 450 500 550 600 650 700 750 nm 105 nm 103 nm 1 nm 103 nm 106 nm (109 nm) 103 m 1 m
Photosynthetic Pigments: The Light Receptors • Pigments are substances that absorb visible light • Different pigments absorb different wavelengths • Wavelengths that are not absorbed are reflected or transmitted • Leaves appear green because chlorophyll reflects and transmits green light © 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc. Animation: Light and Pigments Right-click slide / select “Play”
Chloroplast Light Reflected light Absorbed light Transmitted light Granum Figure 10.8
• A spectrophotometer measures a pigment’s ability to absorb various wavelengths • This machine sends light through pigments and measures the fraction of light transmitted at each wavelength © 2011 Pearson Education, Inc.
Figure 10.9 White light Refracting prism Chlorophyll solution Photoelectric tube Galvanometer Slit moves to 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. TECHNIQUE
• An absorption spectrum is a graph plotting a pigment’s light absorption versus wavelength • The absorption spectrum of chlorophyll a suggests that violet-blue and red light work best for photosynthesis • An action spectrum profiles the relative effectiveness of different wavelengths of radiation in driving a process © 2011 Pearson Education, Inc.
(b) Action spectrum (a) Absorption spectra Engelmann’s experiment (c) Chloro- phyll a Chlorophyll b Carotenoids Wavelength of light (nm) Absorption of light by chloroplast pigments Rate of photosynthesis (measured by O 2 release) Aerobic bacteria Filament of alga 400 500 600 700 400 500 600 700 400 500 600 700 RESULTS Figure 10.10
• Chlorophyll a is the main photosynthetic pigment • Accessory pigments, such as chlorophyll b, broaden the spectrum used for photosynthesis • Accessory pigments called carotenoids absorb excessive light that would damage chlorophyll © 2011 Pearson Education, Inc.
Figure 10.11 Hydrocarbon tail (H atoms not shown) Porphyrin ring CH3 CH3 in chlorophyll a CHO in chlorophyll b
Excitation of Chlorophyll by Light • When a pigment absorbs light, it goes from a ground state to an excited state, which is unstable • When excited electrons fall back to the ground state, photons are given off, an afterglow called fluorescence • If illuminated, an isolated solution of chlorophyll will fluoresce, giving off light and heat © 2011 Pearson Education, Inc.
Figure 10.12 Excited state Heat e Photon (fluorescence) Ground state Photon Chlorophyll molecule Energy of electron (a) Excitation of isolated chlorophyll molecule (b) Fluorescence
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 © 2011 Pearson Education, Inc.
Figure 10.13a (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
Figure 10.13b (b) Structure of photosystem II Thylakoid membrane Chlorophyll STROMA Protein subunits THYLAKOID SPACE
• A primary electron acceptor in the reaction center accepts excited electrons and is reduced as a result • Solar-powered transfer of an electron from a chlorophyll a molecule to the primary electron acceptor is the first step of the light reactions © 2011 Pearson Education, Inc.
• 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 © 2011 Pearson Education, Inc.
• Photosystem I (PS I) is best at absorbing a wavelength of 700 nm • The reaction-center chlorophyll a of PS I is called P700 © 2011 Pearson Education, Inc.
Linear Electron Flow • During the light reactions, there are two possible routes for electron flow: cyclic and linear • Linear electron flow, the primary pathway, involves both photosystems and produces ATP and NADPH using light energy © 2011 Pearson Education, Inc.
• A photon hits a pigment and its energy is passed among pigment molecules until it excites P680 • An excited electron from P680 is transferred to the primary electron acceptor (we now call it P680+) © 2011 Pearson Education, Inc.
Figure 10.14-1 Primary acceptor P680 Light Pigment molecules Photosystem II (PS II) 1 2 e
• P680+ is a very strong oxidizing agent • H2O is split by enzymes, and the electrons are transferred from the hydrogen atoms to P680+, thus reducing it to P680 • O2 is released as a by-product of this reaction © 2011 Pearson Education, Inc.
Figure 10.14-2 Primary acceptor H2O O2 2 H + 1/2 P680 Light Pigment molecules Photosystem II (PS II) 1 2 3 e e e
• Each electron “falls” down an electron transport chain from the primary electron acceptor of PS II to PS I • Energy released by the fall drives the creation of a proton gradient across the thylakoid membrane • Diffusion of H+ (protons) across the membrane drives ATP synthesis © 2011 Pearson Education, Inc.
Figure 10.14-3 Cytochrome complex Primary acceptor H2O O2 2 H + 1/2 P680 Light Pigment molecules Photosystem II (PS II) Pq Pc ATP 1 2 3 5 e e e 4
• In PS I (like PS II), transferred light energy excites P700, which loses an electron to an electron acceptor • P700+ (P700 that is missing an electron) accepts an electron passed down from PS II via the electron transport chain © 2011 Pearson Education, Inc.
Figure 10.14-4 Cytochrome complex Primary acceptor Primary acceptor H2O O2 2 H + 1/2 P680 Light Pigment molecules Photosystem II (PS II) Photosystem I (PS I) Pq Pc ATP 1 2 3 5 6 P700 Light e e 4 e e
• Each electron “falls” down an electron transport chain from the primary electron acceptor of PS I to the protein ferredoxin (Fd) • The electrons are then transferred to NADP+ and reduce it to NADPH • The electrons of NADPH are available for the reactions of the Calvin cycle • This process also removes an H+ from the stroma © 2011 Pearson Education, Inc.
Figure 10.14-5 Cytochrome complex Primary acceptor Primary acceptor H2O O2 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 P700 Light + H NADP NADPH NADP reductase Fd e e e e 4 e e
Photosystem II Photosystem I Mill makes ATP ATP NADPH e e e e e e e Figure 10.15
Cyclic Electron Flow • Cyclic electron flow uses only photosystem I and produces ATP, but not NADPH • No oxygen is released • Cyclic electron flow generates surplus ATP, satisfying the higher demand in the Calvin cycle © 2011 Pearson Education, Inc.
Figure 10.16 Photosystem I Primary acceptor Cytochrome complex Fd Pc ATP Primary acceptor Pq Fd NADPH NADP reductase NADP + H Photosystem II
• Some organisms such as purple sulfur bacteria have PS I but not PS II • Cyclic electron flow is thought to have evolved before linear electron flow • Cyclic electron flow may protect cells from light-induced damage © 2011 Pearson Education, Inc.
A Comparison of Chemiosmosis in Chloroplasts and Mitochondria • Chloroplasts and mitochondria generate ATP by chemiosmosis, but use different sources of energy • Mitochondria transfer chemical energy from food to ATP; chloroplasts transform light energy into the chemical energy of ATP • Spatial organization of chemiosmosis differs between chloroplasts and mitochondria but also shows similarities © 2011 Pearson Education, Inc.
• In mitochondria, protons are pumped to the intermembrane space and drive ATP synthesis as they diffuse back into the mitochondrial matrix • In chloroplasts, protons are pumped into the thylakoid space and drive ATP synthesis as they diffuse back into the stroma © 2011 Pearson Education, Inc.
Mitochondrion Chloroplast 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 Figure 10.17
• 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 H2O to NADPH © 2011 Pearson Education, Inc.
Figure 10.18 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 H2O O2
Concept 10.3: The Calvin cycle uses the chemical energy of ATP and NADPH to reduce CO2 to sugar • The Calvin cycle, like the citric acid cycle, regenerates its starting material after molecules enter and leave the cycle • The cycle builds sugar from smaller molecules by using ATP and the reducing power of electrons carried by NADPH © 2011 Pearson Education, Inc.
• Carbon enters the cycle as CO2 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 CO2 • The Calvin cycle has three phases – Carbon fixation (catalyzed by rubisco) – Reduction – Regeneration of the CO2 acceptor (RuBP) © 2011 Pearson Education, Inc.
Input 3 (Entering one at a time) CO2 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
Input 3 (Entering one at a time) CO2 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
Input 3 (Entering one at a time) CO2 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 CO2 acceptor (RuBP) 3 P P Ribulose bisphosphate (RuBP) 1 P G3P (a sugar) Output Glucose and other organic compounds 3 Figure 10.19-3
Concept 10.4: 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 H2O but also limits photosynthesis • The closing of stomata reduces access to CO2 and causes O2 to build up • These conditions favor an apparently wasteful process called photorespiration © 2011 Pearson Education, Inc.
Photorespiration: An Evolutionary Relic? • In most plants (C3 plants), initial fixation of CO2, via rubisco, forms a three-carbon compound (3-phosphoglycerate) • In photorespiration, rubisco adds O2 instead of CO2 in the Calvin cycle, producing a two- carbon compound • Photorespiration consumes O2 and organic fuel and releases CO2 without producing ATP or sugar © 2011 Pearson Education, Inc.
• Photorespiration may be an evolutionary relic because rubisco first evolved at a time when the atmosphere had far less O2 and more CO2 • 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 © 2011 Pearson Education, Inc.
C4 Plants • C4 plants minimize the cost of photorespiration by incorporating CO2 into four-carbon compounds in mesophyll cells • This step requires the enzyme PEP carboxylase • PEP carboxylase has a higher affinity for CO2 than rubisco does; it can fix CO2 even when CO2 concentrations are low • These four-carbon compounds are exported to bundle-sheath cells, where they release CO2 that is then used in the Calvin cycle © 2011 Pearson Education, Inc.
Figure 10.20a C4 leaf anatomy Photosynthetic cells of C4 plant leaf Mesophyll cell Bundle- sheath cell Vein (vascular tissue) Stoma
Figure 10.20b The C4 pathway Mesophyll cell PEP carboxylase CO2 Oxaloacetate (4C) PEP (3C) Malate (4C) Pyruvate (3C) CO2 Bundle- sheath cell Calvin Cycle Sugar Vascular tissue ADP ATP
• In the last 150 years since the Industrial Revolution, CO2 levels have risen greatly • Increasing levels of CO2 may affect C3 and C4 plants differently, perhaps changing the relative abundance of these species • The effects of such changes are unpredictable and a cause for concern © 2011 Pearson Education, Inc.
CAM Plants • Some plants, including succulents, use crassulacean acid metabolism (CAM) to fix carbon • CAM plants open their stomata at night, incorporating CO2 into organic acids • Stomata close during the day, and CO2 is released from organic acids and used in the Calvin cycle © 2011 Pearson Education, Inc.
Sugarcane Mesophyll cell Bundle- sheath cell C4 CO2 Organic acid CO2 Calvin Cycle Sugar (a) Spatial separation of steps (b) Temporal separation of steps CO2 Organic acid CO2 Calvin Cycle Sugar Day Night CAM Pineapple CO2 incorporated (carbon fixation) CO2 released to the Calvin cycle 2 1 Figure 10.21
Figure 10.21a Sugarcane
Figure 10.21b Pineapple
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 O2 in our atmosphere © 2011 Pearson Education, Inc.

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BioLogy-Photosynthesis-chapterr10ppt.ppt

  • 1.
    LECTURE PRESENTATIONS For CAMPBELLBIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson © 2011 Pearson Education, Inc. Lectures by Erin Barley Kathleen Fitzpatrick Photosynthesis Chapter 10
  • 2.
    Overview: The ProcessThat Feeds the Biosphere • Photosynthesis is the process that converts solar energy into chemical energy • Directly or indirectly, photosynthesis nourishes almost the entire living world © 2011 Pearson Education, Inc.
  • 3.
    • Autotrophs sustainthemselves without eating anything derived from other organisms • Autotrophs are the producers of the biosphere, producing organic molecules from CO2 and other inorganic molecules • Almost all plants are photoautotrophs, using the energy of sunlight to make organic molecules © 2011 Pearson Education, Inc.
  • 4.
  • 5.
    • Photosynthesis occursin plants, algae, certain other protists, and some prokaryotes • These organisms feed not only themselves but also most of the living world © 2011 Pearson Education, Inc.
  • 6.
    © 2011 PearsonEducation, Inc. BioFlix: Photosynthesis
  • 7.
    (a) Plants (b) Multicellular alga (c)Unicellular protists (d) Cyanobacteria (e) Purple sulfur bacteria 10 m 1 m 40 m Figure 10.2
  • 8.
    • Heterotrophs obtaintheir organic material from other organisms • Heterotrophs are the consumers of the biosphere • Almost all heterotrophs, including humans, depend on photoautotrophs for food and O2 © 2011 Pearson Education, Inc.
  • 9.
    • The Earth’ssupply 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 © 2011 Pearson Education, Inc.
  • 10.
  • 11.
    Concept 10.1: Photosynthesisconverts 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 © 2011 Pearson Education, Inc.
  • 12.
    Chloroplasts: The Sitesof 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 © 2011 Pearson Education, Inc.
  • 13.
    • CO2 entersand O2 exits the leaf through microscopic pores called stomata • The chlorophyll is in the membranes of thylakoids (connected sacs in the chloroplast); thylakoids may be stacked in columns called grana • Chloroplasts also contain stroma, a dense interior fluid © 2011 Pearson Education, Inc.
  • 14.
    Figure 10.4 Mesophyll Leaf crosssection Chloroplasts Vein Stomata Chloroplast Mesophyll cell CO2 O2 20 m Outer membrane Intermembrane space Inner membrane 1 m Thylakoid space Thylakoid Granum Stroma
  • 15.
    Mesophyll Leaf cross section ChloroplastsVein Stomata Chloroplast Mesophyll cell CO2 O2 20 m Figure 10.4a
  • 16.
  • 17.
    Tracking Atoms ThroughPhotosynthesis: Scientific Inquiry • Photosynthesis is a complex series of reactions that can be summarized as the following equation: 6 CO2 + 12 H2O + Light energy  C6H12O6 + 6 O2 + 6 H2O © 2011 Pearson Education, Inc.
  • 18.
    The Splitting ofWater • Chloroplasts split H2O into hydrogen and oxygen, incorporating the electrons of hydrogen into sugar molecules and releasing oxygen as a by-product © 2011 Pearson Education, Inc.
  • 19.
  • 20.
    Photosynthesis as aRedox Process • Photosynthesis reverses the direction of electron flow compared to respiration • Photosynthesis is a redox process in which H2O is oxidized and CO2 is reduced • Photosynthesis is an endergonic process; the energy boost is provided by light © 2011 Pearson Education, Inc.
  • 21.
    Figure 10.UN01 Energy 6 CO2  6 H2O C6 H12 O6  6 O2 becomes reduced becomes oxidized
  • 22.
    The Two Stagesof 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 H2O – Release O2 – Reduce NADP+ to NADPH – Generate ATP from ADP by photophosphorylation © 2011 Pearson Education, Inc.
  • 23.
    • The Calvincycle (in the stroma) forms sugar from CO2, using ATP and NADPH • The Calvin cycle begins with carbon fixation, incorporating CO2 into organic molecules © 2011 Pearson Education, Inc.
  • 24.
  • 25.
  • 26.
    Concept 10.2: Thelight reactions convert solar energy to the chemical energy of ATP and NADPH • Chloroplasts are solar-powered chemical factories • Their thylakoids transform light energy into the chemical energy of ATP and NADPH © 2011 Pearson Education, Inc.
  • 27.
    The Nature ofSunlight • Light is a form of electromagnetic energy, also called electromagnetic radiation • Like other electromagnetic energy, light travels in rhythmic waves • Wavelength is the distance between crests of waves • Wavelength determines the type of electromagnetic energy © 2011 Pearson Education, Inc.
  • 28.
    • The electromagneticspectrum is the entire range of electromagnetic energy, or radiation • Visible light consists of wavelengths (including those that drive photosynthesis) that produce colors we can see • Light also behaves as though it consists of discrete particles, called photons © 2011 Pearson Education, Inc.
  • 29.
    Figure 10.7 Gamma rays X-rays UVInfrared Micro- waves Radio waves Visible light Shorter wavelength Longer wavelength Lower energy Higher energy 380 450 500 550 600 650 700 750 nm 105 nm 103 nm 1 nm 103 nm 106 nm (109 nm) 103 m 1 m
  • 30.
    Photosynthetic Pigments: TheLight Receptors • Pigments are substances that absorb visible light • Different pigments absorb different wavelengths • Wavelengths that are not absorbed are reflected or transmitted • Leaves appear green because chlorophyll reflects and transmits green light © 2011 Pearson Education, Inc.
  • 31.
    © 2011 PearsonEducation, Inc. Animation: Light and Pigments Right-click slide / select “Play”
  • 32.
  • 33.
    • A spectrophotometermeasures a pigment’s ability to absorb various wavelengths • This machine sends light through pigments and measures the fraction of light transmitted at each wavelength © 2011 Pearson Education, Inc.
  • 34.
    Figure 10.9 White light Refracting prism Chlorophyll solution Photoelectric tube Galvanometer Slit movesto 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. TECHNIQUE
  • 35.
    • An absorptionspectrum is a graph plotting a pigment’s light absorption versus wavelength • The absorption spectrum of chlorophyll a suggests that violet-blue and red light work best for photosynthesis • An action spectrum profiles the relative effectiveness of different wavelengths of radiation in driving a process © 2011 Pearson Education, Inc.
  • 36.
    (b) Action spectrum (a)Absorption spectra Engelmann’s experiment (c) Chloro- phyll a Chlorophyll b Carotenoids Wavelength of light (nm) Absorption of light by chloroplast pigments Rate of photosynthesis (measured by O 2 release) Aerobic bacteria Filament of alga 400 500 600 700 400 500 600 700 400 500 600 700 RESULTS Figure 10.10
  • 37.
    • Chlorophyll ais the main photosynthetic pigment • Accessory pigments, such as chlorophyll b, broaden the spectrum used for photosynthesis • Accessory pigments called carotenoids absorb excessive light that would damage chlorophyll © 2011 Pearson Education, Inc.
  • 38.
    Figure 10.11 Hydrocarbon tail (Hatoms not shown) Porphyrin ring CH3 CH3 in chlorophyll a CHO in chlorophyll b
  • 39.
    Excitation of Chlorophyllby Light • When a pigment absorbs light, it goes from a ground state to an excited state, which is unstable • When excited electrons fall back to the ground state, photons are given off, an afterglow called fluorescence • If illuminated, an isolated solution of chlorophyll will fluoresce, giving off light and heat © 2011 Pearson Education, Inc.
  • 40.
  • 41.
    A Photosystem: AReaction-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 © 2011 Pearson Education, Inc.
  • 42.
    Figure 10.13a (a) Howa 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
  • 43.
    Figure 10.13b (b) Structureof photosystem II Thylakoid membrane Chlorophyll STROMA Protein subunits THYLAKOID SPACE
  • 44.
    • A primaryelectron acceptor in the reaction center accepts excited electrons and is reduced as a result • Solar-powered transfer of an electron from a chlorophyll a molecule to the primary electron acceptor is the first step of the light reactions © 2011 Pearson Education, Inc.
  • 45.
    • There aretwo 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 © 2011 Pearson Education, Inc.
  • 46.
    • Photosystem I(PS I) is best at absorbing a wavelength of 700 nm • The reaction-center chlorophyll a of PS I is called P700 © 2011 Pearson Education, Inc.
  • 47.
    Linear Electron Flow •During the light reactions, there are two possible routes for electron flow: cyclic and linear • Linear electron flow, the primary pathway, involves both photosystems and produces ATP and NADPH using light energy © 2011 Pearson Education, Inc.
  • 48.
    • A photonhits a pigment and its energy is passed among pigment molecules until it excites P680 • An excited electron from P680 is transferred to the primary electron acceptor (we now call it P680+) © 2011 Pearson Education, Inc.
  • 49.
  • 50.
    • P680+ isa very strong oxidizing agent • H2O is split by enzymes, and the electrons are transferred from the hydrogen atoms to P680+, thus reducing it to P680 • O2 is released as a by-product of this reaction © 2011 Pearson Education, Inc.
  • 51.
  • 52.
    • Each electron“falls” down an electron transport chain from the primary electron acceptor of PS II to PS I • Energy released by the fall drives the creation of a proton gradient across the thylakoid membrane • Diffusion of H+ (protons) across the membrane drives ATP synthesis © 2011 Pearson Education, Inc.
  • 53.
  • 54.
    • In PSI (like PS II), transferred light energy excites P700, which loses an electron to an electron acceptor • P700+ (P700 that is missing an electron) accepts an electron passed down from PS II via the electron transport chain © 2011 Pearson Education, Inc.
  • 55.
  • 56.
    • Each electron“falls” down an electron transport chain from the primary electron acceptor of PS I to the protein ferredoxin (Fd) • The electrons are then transferred to NADP+ and reduce it to NADPH • The electrons of NADPH are available for the reactions of the Calvin cycle • This process also removes an H+ from the stroma © 2011 Pearson Education, Inc.
  • 57.
    Figure 10.14-5 Cytochrome complex Primary acceptor Primary acceptor H2O O2 2 H + 1/2 P680 Light Pigment molecules PhotosystemII (PS II) Photosystem I (PS I) Pq Pc ATP 1 2 3 5 6 7 8 P700 Light + H NADP NADPH NADP reductase Fd e e e e 4 e e
  • 58.
    Photosystem II PhotosystemI Mill makes ATP ATP NADPH e e e e e e e Figure 10.15
  • 59.
    Cyclic Electron Flow •Cyclic electron flow uses only photosystem I and produces ATP, but not NADPH • No oxygen is released • Cyclic electron flow generates surplus ATP, satisfying the higher demand in the Calvin cycle © 2011 Pearson Education, Inc.
  • 60.
  • 61.
    • Some organismssuch as purple sulfur bacteria have PS I but not PS II • Cyclic electron flow is thought to have evolved before linear electron flow • Cyclic electron flow may protect cells from light-induced damage © 2011 Pearson Education, Inc.
  • 62.
    A Comparison ofChemiosmosis in Chloroplasts and Mitochondria • Chloroplasts and mitochondria generate ATP by chemiosmosis, but use different sources of energy • Mitochondria transfer chemical energy from food to ATP; chloroplasts transform light energy into the chemical energy of ATP • Spatial organization of chemiosmosis differs between chloroplasts and mitochondria but also shows similarities © 2011 Pearson Education, Inc.
  • 63.
    • In mitochondria,protons are pumped to the intermembrane space and drive ATP synthesis as they diffuse back into the mitochondrial matrix • In chloroplasts, protons are pumped into the thylakoid space and drive ATP synthesis as they diffuse back into the stroma © 2011 Pearson Education, Inc.
  • 64.
  • 65.
    • ATP andNADPH 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 H2O to NADPH © 2011 Pearson Education, Inc.
  • 66.
    Figure 10.18 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 H2O O2
  • 67.
    Concept 10.3: TheCalvin cycle uses the chemical energy of ATP and NADPH to reduce CO2 to sugar • The Calvin cycle, like the citric acid cycle, regenerates its starting material after molecules enter and leave the cycle • The cycle builds sugar from smaller molecules by using ATP and the reducing power of electrons carried by NADPH © 2011 Pearson Education, Inc.
  • 68.
    • Carbon entersthe cycle as CO2 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 CO2 • The Calvin cycle has three phases – Carbon fixation (catalyzed by rubisco) – Reduction – Regeneration of the CO2 acceptor (RuBP) © 2011 Pearson Education, Inc.
  • 69.
    Input 3 (Entering one ata time) CO2 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
  • 70.
    Input 3 (Entering one ata time) CO2 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
  • 71.
    Input 3 (Entering one ata time) CO2 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 CO2 acceptor (RuBP) 3 P P Ribulose bisphosphate (RuBP) 1 P G3P (a sugar) Output Glucose and other organic compounds 3 Figure 10.19-3
  • 72.
    Concept 10.4: Alternativemechanisms 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 H2O but also limits photosynthesis • The closing of stomata reduces access to CO2 and causes O2 to build up • These conditions favor an apparently wasteful process called photorespiration © 2011 Pearson Education, Inc.
  • 73.
    Photorespiration: An EvolutionaryRelic? • In most plants (C3 plants), initial fixation of CO2, via rubisco, forms a three-carbon compound (3-phosphoglycerate) • In photorespiration, rubisco adds O2 instead of CO2 in the Calvin cycle, producing a two- carbon compound • Photorespiration consumes O2 and organic fuel and releases CO2 without producing ATP or sugar © 2011 Pearson Education, Inc.
  • 74.
    • Photorespiration maybe an evolutionary relic because rubisco first evolved at a time when the atmosphere had far less O2 and more CO2 • 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 © 2011 Pearson Education, Inc.
  • 75.
    C4 Plants • C4plants minimize the cost of photorespiration by incorporating CO2 into four-carbon compounds in mesophyll cells • This step requires the enzyme PEP carboxylase • PEP carboxylase has a higher affinity for CO2 than rubisco does; it can fix CO2 even when CO2 concentrations are low • These four-carbon compounds are exported to bundle-sheath cells, where they release CO2 that is then used in the Calvin cycle © 2011 Pearson Education, Inc.
  • 76.
    Figure 10.20a C4 leafanatomy Photosynthetic cells of C4 plant leaf Mesophyll cell Bundle- sheath cell Vein (vascular tissue) Stoma
  • 77.
    Figure 10.20b The C4pathway Mesophyll cell PEP carboxylase CO2 Oxaloacetate (4C) PEP (3C) Malate (4C) Pyruvate (3C) CO2 Bundle- sheath cell Calvin Cycle Sugar Vascular tissue ADP ATP
  • 78.
    • In thelast 150 years since the Industrial Revolution, CO2 levels have risen greatly • Increasing levels of CO2 may affect C3 and C4 plants differently, perhaps changing the relative abundance of these species • The effects of such changes are unpredictable and a cause for concern © 2011 Pearson Education, Inc.
  • 79.
    CAM Plants • Someplants, including succulents, use crassulacean acid metabolism (CAM) to fix carbon • CAM plants open their stomata at night, incorporating CO2 into organic acids • Stomata close during the day, and CO2 is released from organic acids and used in the Calvin cycle © 2011 Pearson Education, Inc.
  • 80.
    Sugarcane Mesophyll cell Bundle- sheath cell C4 CO2 Organic acid CO2 Calvin Cycle Sugar (a)Spatial separation of steps (b) Temporal separation of steps CO2 Organic acid CO2 Calvin Cycle Sugar Day Night CAM Pineapple CO2 incorporated (carbon fixation) CO2 released to the Calvin cycle 2 1 Figure 10.21
  • 81.
  • 82.
  • 83.
    The Importance ofPhotosynthesis: 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 O2 in our atmosphere © 2011 Pearson Education, Inc.