Chapter 10 Photosynthesis Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings Overview The Process That Feeds the Biosphere Photosynthesis Is the process that converts solar energy into chemical energy Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings Plants and other autotrophs Are the producers of the biosphere Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings Plants are photoautotrophs They use the energy of sunlight to make organic molecules from water and carbon dioxide Figure 10 1 Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings 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 a Plants bacteria which produce sulfur spherical globules c d e LMs c Unicellular protist 10 m e Pruple sulfur bacteria Figure 10 2 b Multicellular algae Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings d Cyanobacteria 40 m 1 5 m Heterotrophs Obtain their organic material from other organisms Are the consumers of the biosphere Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings Concept 10 1 Photosynthesis converts light energy to the chemical energy of food Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings Chloroplasts The Sites of Photosynthesis in Plants The leaves of plants Are the major sites of photosynthesis Leaf cross section Vein Mesophyll Stomata Stomata video Figure 10 3 Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings CO2 O2 Chloroplasts Are the organelles in which photosynthesis occurs Contain thylakoids and grana Mesophyll Chloroplast 5 m Outer membrane Stroma Granum Thylakoid Thylakoid space Intermembrane space Inner membrane 1 m Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings Tracking Atoms Through Photosynthesis Scientific Inquiry Photosynthesis is summarized as 6 CO2 12 H2O Light energy C6H12O6 6 O2 6 H2 O Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings The Splitting of Water Chloroplasts split water into Hydrogen and oxygen incorporating the electrons of hydrogen into sugar molecules Reactants Products 12 H2O 6 CO2 C6H12O6 Figure 10 4 Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings 6 H2O 6 O2 Photosynthesis as a Redox Process Photosynthesis is a redox process Water is oxidized carbon dioxide is reduced Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings The Two Stages of Photosynthesis A Preview Photosynthesis consists of two processes The light reactions The Calvin cycle Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings The light reactions Occur in the grana Split water release oxygen produce ATP and form NADPH Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings The Calvin cycle Occurs in the stroma Forms sugar from carbon dioxide using ATP for energy and NADPH for reducing power Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings An overview of photosynthesis H2O CO2 Light NADP ADP P LIGHT REACTIONS CALVIN CYCLE ATP NADPH Chloroplast Figure 10 5 O2 Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings CH2O sugar Concept 10 2 The light reactions convert solar energy to the chemical energy of ATP and NADPH Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings The Nature of Sunlight Light Is a form of electromagnetic energy which travels in waves Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings Wavelength Is the distance between the crests of waves Determines the type of electromagnetic energy Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings 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 380 450 500 550 Shorter wavelength Figure 10 6 Higher energy Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings 600 650 700 750 nm Longer wavelength Lower energy The visible light spectrum Includes the colors of light we can see Includes the wavelengths that drive photosynthesis Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings Photosynthetic Pigments The Light Receptors Pigments Are substances that absorb visible light Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings Reflect light which include the colors we see Light Reflected Light Chloroplast Absorbed light Granum Transmitted light Figure 10 7 Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings The spectrophotometer Is a machine that sends light through pigments and measures the fraction of light transmitted at each wavelength Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings An absorption spectrum Is a graph plotting light absorption versus wavelength Refracting Chlorophyll prism solution White light 2 Photoelectric tube Galvanometer 3 1 0 100 4 Slit moves to Green pass light light of selected wavelength The high transmittance low absorption reading indicates that chlorophyll absorbs very little green light 0 Figure 10 8 Blue light Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings 100 The low transmittance high absorption reading chlorophyll absorbs most blue light The absorption spectra of chloroplast pigments Provide clues to the relative effectiveness of different wavelengths for driving photosynthesis Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings 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