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Solomon IM Ch 09

Solomon IM Ch 09 - Chapter9:Photosynthesis:CapturingEnergy...

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Chapter 9: Photosynthesis: Capturing Energy 81 9 Photosynthesis: Capturing Energy Lecture Outline I. Light is composed of particles that travel as waves. A. Light is a small part of the electromagnetic spectrum. B. Radiation varies in wavelength. 1. In the visible spectrum, red has longer wavelengths and violet has shorter wavelengths. C. Light is composed of packets of energy called photons. 1. The energy of a photon is inversely related to its wavelength. 2. Short wavelengths have high energy photons. D. When a molecule absorbs a photon of light energy, one electron is energized. 1. This energized electron may return to the ground state and dissipate the energy as heat, or it will fluoresce (emit light). 2. Alternatively, the electron may leave the atom and be accepted by an electron acceptor. a) Electron acceptors are the basis of photosynthesis. II. Photosynthesis in eukaryotes takes place in chloroplasts. A. Chloroplasts typically contain chlorophyll. B. Mesophyll cells contain numerous chloroplasts. C. The chloroplast has a double membrane. 1. The inner membrane encloses the stroma. 2. Thylakoids are a third set of membranes enclosing the thylakoid interior space. 3. Stacks of thylakoids are known as grana. 4. Chlorophyll and other pigments are embedded in the thylakoid membranes. D. Prokaryotes have no chloroplasts, but thylakoid membranes are formed from in foldings of the plasma membrane. E. Chlorophyll is found in the thylakoid membrane. 1. Pigments absorb light of particular wavelengths. 2. Chlorophyll absorbs light in the red and blue regions of the spectrum; therefore it “looks” greenish to our eyes. 3. Chlorophyll molecules are composed of a porphyrin ring, which absorbs energy, and a long tail, which embeds the molecule in the thylakoid membrane. 4. At the center of the porphyrin ring is a magnesium atom. 5. Chlorophyll a is the most important in the light dependent reactions. 6. Chlorophyll b is an accessory pigment that is very similar to chlorophyll a (differs in functional groups of the porphyrin ring). 7. Carotenoids absorb different wavelengths than the chlorophylls. 8. Carotenoids appear yellow and orange to our eyes (think carrots!).
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Instructor’s Manual for Solomon, Berg, and Martin’s Biology, 9 th Edition 82 III. Chlorophyll is the main photosynthetic pigment. A. Absorption spectra plot absorption of light against varying wavelengths. B. Action spectra plot the effectiveness of the varying wavelengths of light. 1. Engelmann in 1883 demonstrated the spectra with Spirogyra . 2. Since the action spectra matched the absorption spectra of chlorophyll, he deduced that chlorophyll was responsible for photosynthesis. 3. Carotenoids widen the action spectrum for photosynthesis. IV. Photosynthesis is the conversion of light energy to chemical bond energy.
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