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 10 Photosynthesis

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Plants are autotrophs – Autotrophs make there own food from energy sources – Are the producers of the biosphere Animals are heterotrophs – Heterotrophs obtain food from the environment – Are the consumers of the biosphere

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Plants, algae, certain other protists, and some bacteria 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 Chloroplasts: The Sites of Photosynthesis in Plants The leaves of plants – Are the major sites of photosynthesis Stomata Guard Cell Xylem and Pholem

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chloroplasts – Are the organelles in which photosynthesis occurs – Contain thylakoids and grana

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Nature of Sunlight Light – Is a form of electromagnetic energy, which travels in waves Wavelength – Is the distance between two peaks – 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 – Reflected light, is 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 The action spectrum of a pigment – Profiles the relative effectiveness of different wavelengths of radiation in driving photosynthesis Rate of photosynthesis (measured by O 2 release) 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. (b)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The action spectrum for photosynthesis – Was first demonstrated by Theodor W. Engelmann Aerobic bacteria Filament of alga 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 O 2 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. (c) Light in the violet-blue and red portions of the spectrum are most effective in driving photosynthesis. CONCLUSION

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chlorophyll absorbs light to start photosynthesis Chlorophyll a – Is the main photosynthetic pigment Chlorophyll b – Is an accessory pigment Other accessory pigments – Carotenoids – Absorb different wavelengths of light and pass the energy to chlorophyll a C CH CH 2 C C C C C CNN C H3CH3C C C C C C C C C N C C C C N Mg H H3CH3C H C CH 2 CH 3 H C H H CH 2 H CH 3 C O O O O O CHO in chlorophyll a in chlorophyll b Porphyrin ring: Light-absorbing “head” of molecule note magnesium atom at center Hydrocarbon tail: interacts with hydrophobic regions of proteins inside thylakoid membranes of chloroplasts: H atoms not shown Figure 10.10