- Slides: 69
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 Chapter 10 Photosynthesis Lectures by Erin Barley Kathleen Fitzpatrick © 2011 Pearson Education, Inc.
Overview: The Process That Feeds the Biosphere • ________is the process that converts solar energy into chemical energy • Directly or indirectly, photosynthesis _____ almost the entire living world © 2011 Pearson Education, Inc.
• _______ sustain themselves without eating anything derived from other organisms • Autotrophs are the producers of the biosphere, producing __________ from CO 2 and other inorganic molecules • Almost all plants are __________, using the energy of sunlight to make organic molecules © 2011 Pearson Education, Inc.
• Photosynthesis occurs in _________, certain other _____, and some _____ • These organisms feed not only themselves but also most of the living world © 2011 Pearson Education, Inc.
Figure 10. 2 (b) Multicellular alga (a) Plants (d) Cyanobacteria (c) Unicellular protists 10 m (e) Purple sulfur 1 m bacteria 40 m
• ________ obtain their organic material from other organisms • Heterotrophs are the _________ of the biosphere • Almost all heterotrophs, including humans, depend on photoautotrophs for _______ © 2011 Pearson Education, Inc.
• The Earth’s supply of ________ was formed from the remains of organisms that died hundreds of millions of years ago • In a sense, fossil fuels represent stores of _________ from the distant past © 2011 Pearson Education, Inc.
Concept 10. 1: Photosynthesis converts light energy to the chemical energy of food • __________ are structurally similar to and likely evolved from photosynthetic bacteria • The ______________ of these cells allows for the chemical reactions of photosynthesis © 2011 Pearson Education, Inc.
Chloroplasts: The Sites of Photosynthesis in Plants • _________ are the major locations of photosynthesis • Their green color is from _________, the green pigment within chloroplasts • Chloroplasts are found mainly in cells of the ________, the interior tissue of the leaf • Each mesophyll cell contains ______ chloroplasts © 2011 Pearson Education, Inc.
• CO 2 enters and O 2 exits the leaf through microscopic pores called _________ • The chlorophyll is in the membranes of ________ (connected sacs in the chloroplast); thylakoids may be stacked in columns called grana • Chloroplasts also contain ______, a dense interior fluid © 2011 Pearson Education, Inc.
Figure 10. 4 a Leaf cross section Chloroplasts Vein Mesophyll Stomata Chloroplast CO 2 Mesophyll cell 20 m
Figure 10. 4 b Chloroplast Thylakoid Stroma Granum Thylakoid space 1 m Outer membrane Intermembrane space Inner membrane
Tracking Atoms Through Photosynthesis: Scientific Inquiry • Photosynthesis is a complex series of reactions that can be summarized as the following equation: ______________________ © 2011 Pearson Education, Inc.
The Splitting of Water • Chloroplasts split ____ into hydrogen and oxygen, incorporating the electrons of hydrogen into _______ molecules and releasing _______ as a by-product © 2011 Pearson Education, Inc.
Figure 10. 5 Reactants: Products: 6 CO 2 C 6 H 12 O 6 12 H 2 O 6 O 2
Photosynthesis as a Redox Process • Photosynthesis ________ the direction of electron flow compared to respiration • Photosynthesis is a redox process in which ______ is oxidized and _____ is reduced • Photosynthesis is an _______ process; the energy boost is provided by light © 2011 Pearson Education, Inc.
Figure 10. UN 01 becomes reduced Energy 6 CO 2 6 H 2 O C 6 H 12 O 6 6 O 2 becomes oxidized
The Two Stages of Photosynthesis: A Preview • Photosynthesis consists of the _______ (the photo part) and ________ (the synthesis part) • The light reactions (in the thylakoids) – – __________ Release _____ Reduce ______ to NADPH Generate ATP from ADP by ________________ © 2011 Pearson Education, Inc.
• The __________ (in the stroma) forms sugar from CO 2, using ATP and NADPH • The Calvin cycle begins with _____________, incorporating CO 2 into organic molecules © 2011 Pearson Education, Inc.
Figure 10. 6 -4 CO 2 H 2 O Light NADP +Pi Light Reactions Calvin Cycle ATP NADPH Chloroplast O 2 [CH 2 O] (sugar)
Concept 10. 2: The light reactions convert solar energy to the chemical energy of ATP and NADPH • _______ are solar-powered chemical factories • Their thylakoids transform light energy into the chemical energy of _____ and _____ © 2011 Pearson Education, Inc.
The Nature of Sunlight • Light is a form of electromagnetic energy, also called _________________ • Like other electromagnetic energy, light travels in rhythmic ________ • ________ is the distance between crests of waves • _________ determines the type of electromagnetic energy © 2011 Pearson Education, Inc.
• The ___________ is the entire range of electromagnetic energy, or radiation • ____________ 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 __________ © 2011 Pearson Education, Inc.
Figure 10. 7 10 5 nm 10 3 nm 103 1 nm Gamma X-rays UV nm 1 m (109 nm) 106 nm Infrared Microwaves 103 m Radio waves Visible light 380 450 500 Shorter wavelength Higher energy 550 600 650 700 750 nm Longer wavelength Lower energy
Photosynthetic Pigments: The Light Receptors • ________are substances that absorb visible light • Different pigments absorb different _____ • Wavelengths that are not absorbed are _______ or _________ • Leaves appear green because chlorophyll _______ and _______ green light © 2011 Pearson Education, Inc.
Figure 10. 8 Light Reflected light Chloroplast Absorbed light Granum Transmitted light
• A ___________ measures a pigment’s ability to absorb various wavelengths • This machine sends light through pigments and measures the fraction of light _______ at each wavelength © 2011 Pearson Education, Inc.
Figure 10. 9 TECHNIQUE Refracting Chlorophyll Photoelectric solution tube White prism Galvanometer light 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.
• An ___________ is a graph plotting a pigment’s light absorption versus wavelength • The absorption spectrum of ________ suggests that violet-blue and red light work best for photosynthesis • An __________ profiles the relative effectiveness of different wavelengths of radiation in driving a process © 2011 Pearson Education, Inc.
(a) Absorption spectra (b) Action spectrum Absorption of light by chloroplast pigments RESULTS Rate of photosynthesis (measured by O 2 release) Figure 10. 10 Chlorophyll a Chlorophyll b Carotenoids 400 500 600 Wavelength of light (nm) 400 500 600 700 Aerobic bacteria Filament of alga (c) Engelmann’s experiment 400 500 600 700
• The action spectrum of photosynthesis was first demonstrated in 1883 by Theodor W. ________ • In his experiment, he exposed different segments of a filamentous alga to different wavelengths • Areas receiving wavelengths favorable to photosynthesis produced excess _______ • He used the growth of aerobic bacteria clustered along the alga as a measure of O 2 production © 2011 Pearson Education, Inc.
• _________ is the main photosynthetic pigment • Accessory pigments, such as _______, broaden the spectrum used for photosynthesis • Accessory pigments called ________ absorb excessive light that would damage chlorophyll © 2011 Pearson Education, Inc.
Figure 10. 11 CH 3 in chlorophyll a CHO in chlorophyll b Porphyrin ring Hydrocarbon tail (H atoms not shown)
Excitation of Chlorophyll by Light • When a pigment absorbs light, it goes from a ______ state to an _______ state, which is unstable • When excited electrons fall back to the ground state, photons are given off, an afterglow called __________ • If illuminated, an isolated solution of chlorophyll will fluoresce, giving off _________ © 2011 Pearson Education, Inc.
Figure 10. 12 Energy of electron e Excited state Heat Photon (fluorescence) Photon Chlorophyll molecule Ground state (a) Excitation of isolated chlorophyll molecule (b) Fluorescence
A Photosystem: A Reaction-Center Complex Associated with Light-Harvesting Complexes • A ________ consists of a _______________ (a type of protein complex) surrounded by light-harvesting complexes • The ______________ (pigment molecules bound to proteins) transfer the energy of photons to the reaction center © 2011 Pearson Education, Inc.
Figure 10. 13 a Lightharvesting complexes Thylakoid membrane Photon Photosystem Reactioncenter complex STROMA Primary electron acceptor e Transfer of energy Pigment Special pair of molecules chlorophyll a molecules THYLAKOID SPACE (INTERIOR OF THYLAKOID) (a) How a photosystem harvests light
Thylakoid membrane Figure 10. 13 b Chlorophyll Protein subunits (b) Structure of photosystem II STROMA THYLAKOID SPACE
• A _______________ in the reaction center accepts excited electrons and is reduced as a result • Solar-powered transfer of an electron from a ___________ molecule to the _____________ is the first step of the light reactions © 2011 Pearson Education, Inc.
• There are _______ types of photosystems in the thylakoid membrane • ___________ functions first (the numbers reflect order of discovery) and is best at absorbing a wavelength of _______ • The reaction-center chlorophyll a of PS II is called ______ © 2011 Pearson Education, Inc.
• __________ is best at absorbing a wavelength of ________ • The reaction-center chlorophyll a of PS I is called ________ © 2011 Pearson Education, Inc.
Linear Electron Flow • During the light reactions, there are two possible routes for electron flow: ____ and _______ • ____________, 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 ______ • An excited electron from P 680 is transferred to the _________________ (we now call it ______) © 2011 Pearson Education, Inc.
• P 680+ is a very strong _______ agent • _____ is split by enzymes, and the electrons are transferred from the hydrogen atoms to P 680+, thus reducing it to P 680 • ______ is released as a by-product of this reaction © 2011 Pearson Education, Inc.
• Each electron “_____” 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 ________ across the thylakoid membrane • Diffusion of H+ (protons) across the membrane drives _________ © 2011 Pearson Education, Inc.
• In _____ (like PS II), transferred light energy excites P 700, which loses an electron to an electron acceptor • ______ (P 700 that is missing an electron) accepts an electron passed down from PS II via the electron transport chain © 2011 Pearson Education, Inc.
• Each electron “falls” down an electron transport chain from the primary electron acceptor of PS I to the protein _______ • The electrons are then transferred to _______ and reduce it to _____ • The electrons of NADPH are available for the reactions of the _______ cycle • This process also removes an _____ from the stroma © 2011 Pearson Education, Inc.
Figure 10. 14 -5 Ele ct Primary acceptor 2 H + 1/ O 2 2 H 2 O e 2 ron Pq Primary acceptor 4 tran spo rt c hai n e Cytochrome complex E tra lect ch ns ron ai po n rt 7 Fd e e 8 NADP reductase 3 Pc e e P 700 5 P 680 Light 1 Light 6 ATP Pigment molecules Photosystem II (PS II) Photosystem I (PS I) NADP + H NADPH
Figure 10. 15 e e Mill makes ATP e Photo n e NADPH e Photo n ATP Photosystem II Photosystem I
Cyclic Electron Flow • __________ uses only photosystem I and produces ATP, but not NADPH • No ________ is released • Cyclic electron flow generates surplus _______, satisfying the higher demand in the Calvin cycle © 2011 Pearson Education, Inc.
Figure 10. 16 Primary acceptor Fd Fd Pq NADP reductase Cytochrome complex NADPH Pc Photosystem II ATP NADP + H
• Some organisms such as __________ have PS I but not PS II • __________ is thought to have evolved before linear electron flow • Cyclic electron flow may protect cells from ___________ © 2011 Pearson Education, Inc.
A Comparison of Chemiosmosis in Chloroplasts and Mitochondria • Chloroplasts and mitochondria generate ATP by ________, but use different sources of energy • Mitochondria transfer _________ from food to ATP; chloroplasts transform ______ into the chemical energy of ATP • _________ of chemiosmosis differs between chloroplasts and mitochondria but also shows similarities © 2011 Pearson Education, Inc.
• In mitochondria, protons are pumped to the _________ and drive ATP synthesis as they diffuse back into the mitochondrial matrix • In chloroplasts, protons are pumped into the ________ and drive ATP synthesis as they diffuse back into the stroma © 2011 Pearson Education, Inc.
Figure 10. 17 Chloroplast Mitochondrion CHLOROPLAST STRUCTURE MITOCHONDRION STRUCTURE H Intermembrane space Inner membrane Matrix Diffusion Electron transport chain Thylakoid membrane ATP synthase Stroma ADP P i Key [H ] Higher Lower [H ] Thylakoid space H ATP
• ____________ are produced on the side facing the stroma, where the ___________ takes place • In summary, light reactions ________ and increase the potential energy of electrons by moving them from __________ © 2011 Pearson Education, Inc.
Figure 10. 18 STROMA (low H concentration) Photosystem II Light 4 H+ Cytochrome complex Photosystem I Light NADP reductase 3 Fd Pq H 2 O NADPH Pc 2 1 THYLAKOID SPACE (high H concentration) 1/ 2 NADP + H O 2 +2 H+ 4 H+ To Calvin Cycle Thylakoid membrane STROMA (low H concentration) ATP synthase ADP + Pi ATP H+
Concept 10. 3: The Calvin cycle uses the chemical energy of ATP and NADPH to reduce CO 2 to sugar • The _________, like the citric acid cycle, regenerates its starting material after molecules enter and leave the cycle • The cycle builds ______ from smaller molecules by using _____ and the reducing power of electrons carried by _______ © 2011 Pearson Education, Inc.
• Carbon enters the cycle as CO 2 and leaves as a sugar named ____________ • For net synthesis of 1 G 3 P, the cycle must take place ______, fixing ___ molecules of CO 2 • The Calvin cycle has three phases – ________ (catalyzed by _____) – __________________________ © 2011 Pearson Education, Inc.
Figure 10. 19 -3 Input (Entering one CO 2 at a time) 3 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 (Ru. BP) 6 NADPH 6 NADP 6 Pi P 5 G 3 P 6 P Glyceraldehyde 3 -phosphate (G 3 P) 1 P G 3 P (a sugar) Output Glucose and other organic compounds Phase 2: Reduction
Concept 10. 4: Alternative mechanisms of carbon fixation have evolved in hot, arid climates • _________ is a problem for plants, sometimes requiring trade-offs with other metabolic processes, especially photosynthesis • On hot, dry days, plants close ____, which conserves _____ but also limits _______ • The closing of stomata reduces access to ______ and causes _____ to build up • These conditions favor an apparently wasteful process called _____________ © 2011 Pearson Education, Inc.
Photorespiration: An Evolutionary Relic? • In most plants (_______), initial fixation of CO 2, via ______, forms a ______ compound (3 -phosphoglycerate) • In photorespiration, rubisco adds ____ instead of _____ in the Calvin cycle, producing a _______ compound • Photorespiration consumes ____ and _______ and releases ______ 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 O 2 and more CO 2 • 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 ______ of the carbon fixed by the Calvin cycle © 2011 Pearson Education, Inc.
C 4 Plants • _______ minimize the cost of photorespiration by incorporating CO 2 into _______ compounds in mesophyll cells • This step requires the enzyme _______ • PEP carboxylase has a higher affinity for _____ than rubisco does; it can _____ even when CO 2 concentrations are low • These four-carbon compounds are exported to _______, where they release ______ that is then used in the Calvin cycle © 2011 Pearson Education, Inc.
Figure 10. 20 The C 4 pathway C 4 leaf anatomy Mesophyll cell PEP carboxylase Mesophyll cell Photosynthetic cells of C 4 Bundleplant leaf sheath cell Oxaloacetate (4 C) Vein (vascular tissue) PEP (3 C) ADP Malate (4 C) Stoma Bundlesheath cell CO 2 ATP Pyruvate (3 C) CO 2 Calvin Cycle Sugar Vascular tissue
• In the last 150 years since the Industrial Revolution, _____ levels have risen greatly • Increasing levels of CO 2 may affect C 3 and C 4 plants differently, perhaps changing the ___________ of these species • The effects of such changes are unpredictable and a cause for concern © 2011 Pearson Education, Inc.
CAM Plants • Some plants, including ________, use ________________ to fix carbon • ________ open their stomata at night, incorporating CO 2 into organic acids • ________ close during the _______, and CO 2 is released from organic acids and used in the Calvin cycle © 2011 Pearson Education, Inc.
Figure 10. 21 Sugarcane Pineapple C 4 Mesophyll Organic acid cell CAM CO 2 1 CO 2 incorporated (carbon fixation) Organic acid Calvin Cycle Night CO 2 Bundlesheath cell CO 2 2 CO 2 released to the Calvin cycle Sugar (a) Spatial separation of steps Calvin Cycle Day Sugar (b) Temporal separation of steps
The Importance of Photosynthesis: A Review • The energy entering chloroplasts as sunlight gets stored as _______________ • Sugar made in the chloroplasts supplies chemical energy and carbon skeletons to synthesize the organic molecules of cells • Plants store excess sugar as _____ in structures such as ____________ • In addition to food production, photosynthesis produces the _____ in our atmosphere © 2011 Pearson Education, Inc.