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CH09-Photosynthesis-part-01 - CHAPTER 9 PHOTOSYNTHESIS...

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Unformatted text preview: CHAPTER 9: PHOTOSYNTHESIS - CAPTURING ENERGY I Two Light-dependent reactions Carbon fixation (Dark) reactions Phases: - Occurs in Thylakoids of chloroplasts - Occurs in The si'roma of chloroplasts I - Converts ligh'i' energy To chemical energy - Uses ATP and NADPH - Ligh’r energy spli‘is wa‘ier, makes ATP, - Inorganic carbon from CO2 is and reduces NADP+ —> NADPH incorporated into organic molecules Light I - energy Light—dependent reactions Carbon fixation reactions (in thylakoids) (in stroma) - '; — - — _ _ _ _______._* Chloroplast @ Carbohydrates Summary reaction: '— RedUCtiOH j Lightenergy 6CO2 'l' H20 —)' cal—“206 'l' 602 'l' Chlorophyll Carbon Water Glucose Oxygen Water dioxide I l— Oxidation Redox: electrons (and W) are Transferred from HZO To C02 — light energy is Transferred as well TABLE 9-3 Summary of Photosynthesis Reaction Series Summary of Process Needed Materials End Products Light-dependent reactions Energy from sunlight used to split water. manufacture ATP. and {take place in thyiakoid reduce NADP' membranes} Photochemical reactiorts Chlorophyllactivatod: reactiort comer gives up photoexcited Light energy; pigments Electrons electron to electron acceptor (chlorophyll) Electron transport Electrons transported along chain of etectron acceptors in Electrons. NADP'. H30. NADPH‘ O, thylakoid membranes: electrons reduce NADP‘; splitting of water electron acceptors provides some H‘ that accumulates inside rhylakoid space Chemiosmosrs H‘ permitted to difluse across the thylakoid membrane down Proton gradient. ATP their gradient; they cross the membrane through special channels ADP + PII in ATP synthase complex: energy released is used to produce ATP ATP synthase Carbon fixation reactions Carbon fixation: Carbon dioxide used to make carbohydrate Ribulose bisphosphate. Carbohydrates, (take place in stroma] CO). ATP. NADPH, ADP + Pl. NADP' necessary enzymes ELECTROMAGNETIC mitfllL-C’Eliiaiy wavelengths (ls) IS THE RADIANT ENERGY FLOWING FROM THE SUN Figure 9-1 p 192 radio " ' waves -Travels as waves Micro- °Photons = particles of light energy waves -Energy of photon varies with 7h: shorter 7t. > longer 7t. '"lrar9d Visible Longer A (less energetic) One wavelength (7L) i—'—i /W\ Longer wavelength 760 nm Visible light (380-760 nm) as humans can see 600 nm Shorter x (more energetic) Electromagnetic spectrum INTERACTIONS BETWEEN PHOTONS and MATTER Figure 9—3 193 Electron pushed into orbital in higher energy shell (unstable) Fluorescence emission of light The electron may return 500 nm - 400 nrn 380 nm JVWVV\ Shorter wavelength Photon is absorbed by an excitable electron that moves into a higher energy level. to ground level by emitting a less energetic photon. Electron acceptor molecule Low energy level High energy level or Capturing energy \ in photosynthesis The electron may be accepted by an electron acceptor molecule. CHLOROPLASTS REVISITED — TRIPLE MEMBRANE ORGANELLES ‘I' Stroma — fluid-filled space surrounding thylakoids Inner membrane Outer membrane Intermembrane Thylakoid Thylakoid Granum space membrane lumen (stack of ' thylakoids) (c) In the chloroplast, pigments necessary for the light-capturing reactions of photosynthesis are part of thylakoid membranes, whereas the enzymes for the synthesis of carbohydrate molecules are in the stroma. Figure 9-4 p 194 /in chlorophyll in CHO CHLOROPHYLL a if MAINLIGHT-ABSORBING l. l? c, PHOTOSYNTHETIC PIGMENT popphyrmping Has—c<\\zc-/c‘/ ‘\‘ I (I: IQ—CHJJHJ Figure 9-5 p 195 With magnesium f—‘rx .,I.~I='c' .. absorbs light H -' s” s H on; Hc—c=o CH; tlz=o c:a (I) 0 cu; in chlorophyll a Hydrocarbon (Phytol) “tail” anchors molecule in thylakoid membrane ABSORPTION SPECTRUM 0t CHLOROPHYLL Accessory pigments absorb different )6 of light than chlorophyll a -Chlorophyll b: yellow-green pigment -Corotenoids: yellow and orange pigments I | l 4—. Chlorophyll b Chlorophyll a Estimated absorption (“/01 400 500 600 700 Wavelength (nm) (a) Chlorophylls a and b absorb light mainly in the blue (422 to 492 nm) and rod (647 to 760 nm) regions. ACTION SPECTRUM of PHOTOSVNTHESIS ' 100 " Most effective ls for photosynthesis 43 O) CO C) C} O M C} Relative rate of photosynthesis 400 500 600 700 Wavelength (nm) (b) The action spectrum of photosynthesis indicates the effective- ness of various wavelengths of light in powering photosynthesis. Many plant species have action spectra for photosynthesis that resemble the generalized action spectrum shown here. ...
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