Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Chapter 8 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 – Builds organic compounds that provide the energy and building material for ecosystems

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Plants and other autotrophs are the producers of the biosphere 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 bacteria, which produce sulfur (spherical globules) (c, d, e: LMs). (a) Plants (b) Multicellular algae (c) Unicellular protist 10  m 40  m (d) Cyanobacteria 1.5  m (e) Pruple sulfur bacteria Figure 10.2

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Heterotrophs – Obtain their organic material from other organisms – Are the consumers of the biosphere

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 Vein Leaf cross section Figure 10.3 Mesophyll CO 2 O2O2 Stomata

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chloroplasts – Are the organelles in which photosynthesis occurs – Contain thylakoids and grana Chloroplast Mesophyll 5 µm Outer membrane Intermembrane space Inner membrane Thylakoid space Thylakoid Granum Stroma 1 µm

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Stomata Where oxygen and CO2 gas exchange occurs

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Tracking Atoms Through Photosynthesis: Scientific Inquiry Photosynthesis is summarized as 6 CO H 2 O + Light energy  C 6 H 12 O O H 2 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 6 CO 2 12 H 2 O Reactants: Products: C 6 H 12 O 6 6H2O6H2O 6O26O2 Figure 10.4

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 H2OH2O CO 2 Light LIGHT REACTIONS CALVIN CYCLE Chloroplast [CH 2 O] (sugar) NADPH NADP  ADP + P O2O2 Figure 10.5 ATP

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 Gamma rays X-raysUVInfrared Micro- waves Radio waves 10 –5 nm 10 –3 nm 1 nm 10 3 nm 10 6 nm 1 m 10 6 nm 10 3 m nm Visible light Shorter wavelength Higher energy Longer wavelength Lower energy Figure 10.6

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 Figure 10.8 White light Refracting prism Chlorophyll solution Photoelectric tube Galvanometer Slit moves to pass light of selected wavelength Green light The high transmittance (low absorption) reading indicates that chlorophyll absorbs very little green light. The low transmittance (high absorption) reading chlorophyll absorbs most blue light. Blue light

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 (a) Absorption spectra. The three curves show the wavelengths of light best absorbed by three types of chloroplast pigments. Wavelength of light (nm) Chlorophyll b Carotenoids

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In the Thylakoids: We find the photosystems – Is composed of a reaction center surrounded by a number of light-harvesting complexes Primary election acceptor Photon Thylakoid Light-harvesting complexes Reaction center Photosystem STROMA Thylakoid membrane Transfer of energy Special chlorophyll a molecules Pigment molecules THYLAKOID SPACE (INTERIOR OF THYLAKOID) Figure e–e–

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Light Reactions- Photosystems (in the Thylakoid) Produces NADPH, ATP, and oxygen Figure Photosystem II (PS II) Photosystem-I (PS I) ATP NADPH NADP + ADP CALVIN CYCLE CO 2 H2OH2O O2O2 [CH 2 O] (sugar) LIGHT REACTIONS Light Primary acceptor Pq Cytochrome complex PC e P680 e–e– e–e– O2O2 + H2OH2O 2 H + Light ATP Primary acceptor Fd e e–e– NADP + reductase Electron Transport chain Electron transport chain P700 Light NADPH NADP H + + H NADPH stands for: nicotinamide adenine dinucleotide phosphate DON’T WORRY: you don’t have to know this

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Light Reactions The light reactions: the organization of the thylakoid membrane LIGHT REACTOR NADP + ADP ATP NADPH CALVIN CYCLE [CH 2 O] (sugar) STROMA (Low H + concentration) Photosystem II LIGHT H2OH2O CO 2 Cytochrome complex O2O2 H2OH2O O2O2 1 1⁄21⁄2 2 Photosystem I Light THYLAKOID SPACE (High H + concentration) STROMA (Low H + concentration) Thylakoid membrane ATP synthase Pq Pc Fd NADP + reductase NADPH + H + NADP + + 2H + To Calvin cycle ADP P ATP 3 H+H+ 2 H + +2 H + 2 H + Figure 10.17

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Next step: The Calvin Cycle The Calvin cycle uses ATP and NADPH to convert CO 2 to sugar The Calvin cycle – Occurs in the stroma

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Calvin cycle (G3P) Input (Entering one at a time) CO 2 3 Rubisco Short-lived intermediate 3 PP P Ribulose bisphosphate (RuBP) P 3-Phosphoglycerate P6 P 6 1,3-Bisphoglycerate 6 NADPH 6 NADPH + 6 P P 6 Glyceraldehyde-3-phosphate (G3P) 6 ATP 3 ATP 3 ADP CALVIN CYCLE P 5 P 1 G3P (a sugar) Output Light H2OH2O CO 2 LIGHT REACTION ATP NADPH NADP + ADP [CH 2 O] (sugar) CALVIN CYCLE Figure O2O2 6 ADP Glucose and other organic compounds Phase 1: Carbon fixation Phase 2: Reduction Phase 3: Regeneration of the CO 2 acceptor (RuBP) Use ATP and NADPH to convert CO 2 to sugars

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Importance of Photosynthesis: A Review A review of photosynthesis Light reactions: Are carried out by molecules in the thylakoid membranes Convert light energy to the chemical energy of ATP and NADPH Split H 2 O and release O 2 to the atmosphere Calvin cycle reactions: Take place in the stroma Use ATP and NADPH to convert CO 2 to sugars Return ADP, inorganic phosphate, and NADP+ to the light reactions O2O2 CO 2 H2OH2O Light Light reaction Calvin cycle NADP + ADP ATP NADPH + P 1 RuBP 3-Phosphoglycerate Amino acids Fatty acids Starch (storage) Sucrose (export) G3P Photosystem II Electron transport chain Photosystem I Chloroplast Figure 10.21