Chapter 10 Photosynthesis PowerPoint Lectures for Biology Eighth Edition Neil Campbell and Jane Reece Photosynthesis Occurs in plants algae certain other protists and some prokaryotes These organisms use light energy to drive the synthesis of organic molecules from carbon dioxide and in most cases water They feed not only themselves but the entire living world a On land plants are the predominant producers of food In aquatic environments photosynthetic organisms include b multicellular algae such as this kelp c some unicellular protists such as Euglena d the prokaryotes called cyanobacteria and e other photosynthetic prokaryotes such as these purple sulfur bacteria which produce sulfur spherical globules c d e LMs a Plants c Unicellular protist 10 m e Pruple sulfur bacteria Figure 10 2 b Multicellular algae d Cyanobacteria 40 m 1 5 m The leaves of plants Are the major sites of photosynthesis Leaf cross section Vein Mesophyll Figure 10 3 Stomata CO2 O2 Chloroplasts The Sites of Photosynthesis in Plants Mesophyll Chloroplast 5 m Outer membrane Thylakoid Stroma Granum Intermembrane space Thylakoid space Inner membrane 1 m Tracking Atoms Through Photosynthesis Scientific Inquiry Photosynthesis is summarized as 6 CO2 12 H2O Light energy C6H12O6 6 O2 6 H2 O Photosynthesis is a redox process Water is oxidized carbon dioxide is reduced The Splitting of Water Chloroplasts split water into Hydrogen and oxygen incorporating the electrons of hydrogen into sugar molecules Reactants Products Figure 10 4 12 H2O 6 CO2 C6H12O6 6 H2O 6 O2 An overview of photosynthesis H2O CO2 Light NADP ADP P LIGHT REACTIONS CALVIN CYCLE ATP NADPH Chloroplast Figure 10 5 O2 CH2O sugar The electromagnetic spectrum Is the entire range of electromagnetic energy or radiation 10 5 nm 1 nm 10 3 nm Gamma rays X rays UV 1m 106 nm 106 nm 103 nm Infrared Microwaves 103 m Radio waves Visible light 380 450 500 Shorter wavelength Figure 10 6 Higher energy 550 600 650 700 750 nm Longer wavelength Lower energy Photosynthetic Pigments The Light Receptors Pigments Are substances that absorb visible light The colors that we see are wavelengths of light that are reflected or not absorbed Light Reflected Light Chloroplast Absorbed light Figure 10 7 Granum Transmitted light The absorption spectra of three types of pigments in chloroplasts Three different experiments helped reveal which wavelengths of light are photosynthetically important The results are shown below EXPERIMENT RESULTS Absorption of light by chloroplast pigments Chlorophyll a Chlorophyll b Carotenoids Wavelength of light nm a Absorption spectra The three curves show the wavelengths of light best absorbed by three types of chloroplast pigments Figure 10 9 The action spectrum of a pigment Rate of photosynthesis measured by O2 release Profiles the relative effectiveness of different wavelengths of radiation in driving photosynthesis b Action spectrum This graph plots the rate of photosynthesis versus wavelength The resulting action spectrum resembles the absorption spectrum for chlorophyll a but does not match exactly see part a This is partly due to the absorption of light by accessory pigments such as chlorophyll b and carotenoids The action spectrum for photosynthesis Was first demonstrated by Theodor W Engelmann Aerobic bacteria Filament of alga 500 600 700 400 c Engelmann s experiment In 1883 Theodor W Engelmann illuminated a filamentous alga with light that had been passed through a prism exposing different segments of the alga to different wavelengths He used aerobic bacteria which concentrate near an oxygen source to determine which segments of the alga were releasing the most O2 and thus photosynthesizing most Bacteria congregated in greatest numbers around the parts of the alga illuminated with violet blue or red light Notice the close match of the bacterial distribution to the action spectrum in part b CONCLUSION photosynthesis Light in the violet blue and red portions of the spectrum are most effective in driving Chlorophyll a CH3 in chlorophyll a CHO in chlorophyll b CH2 CH C H3 C C C C H C N C N C C C H H CH2 N C C O C H C CH3 CH3 Porphyrin ring Light absorbing head of molecule note magnesium atom at center C C O O CH2 C C C CH2 C C Mg C H C N C H3C CH3 H O O CH3 CH2 Hydrocarbon tail interacts with hydrophobic regions of proteins inside thylakoid membranes of chloroplasts H atoms not shown Figure 10 10 Excitation of Chlorophyll by Light When a pigment absorbs light It goes from a ground state to an excited state which is unstable Energy of election e If an isolated solution of chlorophyll is illuminated It will fluoresce giving off light and heat Excited state Heat Photon fluorescence Photon Figure 10 11 A Chlorophyll molecule Ground state Figure 10 11 B Thylakoid Photosystem Photon STROMA Thylakoid membrane Light harvesting complexes Primary election acceptor e Transfer of energy Figure 10 12 Reaction center Special chlorophyll a molecules Pigment molecules THYLAKOID SPACE INTERIOR OF THYLAKOID Noncyclic electron flow Produces NADPH ATP and oxygen H2 O CO2 Light NADP ADP CALVIN CYCLE LIGHT REACTIONS ATP NADPH O2 CH2O sugar Primary acceptor Primary acceptor Elec tr 2 2 H O2 e H2O Pq 7 4 on t ra ns por t Fd c ha i e n NADP reductase 3 e 5 H P700 P680 Light ATP Photosystem II PS II NADP 2 H NADPH PC 6 Figure 10 13 8 e Cytochrome complex e Light 1 El Tra ectro ns n ch por a in t Photosystem I PS I A mechanical analogy for the light reactions e ATP e e NADPH e Mill makes ATP e on Phot e Figure 10 14 P h ot o n e Photosystem II Photosystem I Primary acceptor Primary acceptor Fd Fd Pq NADP reductase Cytochrome complex Pc Figure 10 15 Photosystem II ATP Photosystem I NADP NADPH The spatial organization of chemiosmosis Differs in chloroplasts and mitochondria Key Higher H Lower H Chloroplast Mitochondrion CHLOROPLAST STRUCTURE MITOCHONDRION STRUCTURE Intermembrance space Membrance Matrix Figure 10 16 H Diffusion Electron transport chain ATP Synthase ADP Thylakoid space Stroma P H ATP The light reactions and chemiosmosis the organization of the thylakoid membrane H2O CO2 LIGHT NADP ADP LIGHT REACTOR CALVIN CYCLE ATP NADPH STROMA Low H concentration O2 CH2O sugar Cytochrome Photosystem II complex Photosystem I Light 2 H NADP reductase Fd 3 NADP 2H NADPH H Pq H2 O THYLAKOID SPACE High H concentration Pc 2 1 1 2 O2 2 H 2 H To Calvin cycle STROMA Low H concentration Thylakoid membrane ATP synthase ADP ATP P Figure 10 17 H The Calvin cycle H2O Light CO2 Input 3 Entering
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