CH 8: Photosynthesis

CH 8: Photosynthesis

1. Anoxygenic Photosynthesis

   • does not produce oxygen
   • 4 different bacterial groups: purple, green sulfur, green nonsulfur, and heliobacteria
   • releases sulfur

2. Oxygenic Photosynthesis

   • does produce oxygen
   • in cyanobacteria, 7 groups of algae, ALL land plants

3. photosynthesis takes place in leaves

   • cells of plant leaves have chloroplasts
     • CHLOROPLASTS
       • GRANA: stacks of flattened sacs of thylakoid membrane
         • THYLAKOID MEMBRANE: internal membrane
           • contains chlorophyll and other photosynthetic pigments
             • pigments clustered into photosystems
               • PIGMENTS
                 • molecules that absorb light energy in visible range
                 • PHOTON: particle of light; discrete bundle of energy
                 • PHOTOELECTRIC EFFECT: removal of an electron from a molecule by light
                 • 2 types in green plant photosynthesis
                   • CHLOROPHYLLS
                     • CHLOROPHYLL a
                       • main pigment
                       • directly converts light energy to chemical energy
                       • absorbs violet-blue and red light
                     • CHLOROPHYLL b
                       • accessory pigment
                       • absorbs light wavelengths that chlorophyll a does not absorb
                     • CHLOROPHYLL STRUCTURE
                       • PORPHYRIN RING
                         • alternating double and single bonds
                         • magnesium ion center
                       • photons excite electrons in ring
                       • electrons shuttled away from ring
                   • CAROTENOIDS
       • STROMA: semiliquid surrounding thylakoid membranes

4. Photosynthesis takes place in 3 stages

   • LIGHT DEPENDENT REACTION
     • STAGE 2: uses energy to make ATP and to reduce compound NADP+ to NADPH
     • STAGE 1: captures energy from sunlight
   • LIGHT-INDEPENDENT REACTION
     • STAGE 3: uses ATP and NADPH to power synthesis of organic molecules
       • CARBON FIXATION: formation of organic molecules from CO2

5. TYPES OF PHOTOSYNTHESIS

   • C3
     • fix carbon using the Calvin cycle
   • C4
     • spatial (place) solution
     • fix carbon using PEP carboxylase in mesophyll cells
       • carbon dioxide is then released into bundle-sheath cells for carbon fixation by the Calvin cycle
     • to produce a single glucose requires 12 additional ATP
     • advantageous in hot dry climates, photorespiration removes more than half of carbon fixed by C3 pathway
     • corn, sugarcane, grasses, sorghum
   • CAM
     • temporal (time) solution
     • succulents, cacti, pineapples
     • stomata open during day, close at night
       • when stomata closed during day, organic acids are decarboxylated to yield high levels of carbon dioxide
         • high levels of carbon dioxide drive Calvin cycle and minimize photorespiration
     • fix carbon dioxide using PEP carboxylase during night and store in vacuole

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