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					        Chapter 8 -
                                            Photosynthesis occurs in…
      Photosynthesis
6CO2 + 6H2O + light → C6H12O6 + 6O2         Plants, algae, some
      The capture and conversion of solar
                                            bacteria
       energy to chemical bond energy




   Not all plants are                        Photosynthesis occurs in
                                                   chloroplasts
    photosynthetic
Some parasitic plants are not
photosynthetic




  Photosynthetic products are                Chlorophyll is the primary
     utilized in respiration                  photosynthetic pigment




                                                                          1
Chlorophyll absorbs specific            1883 – T.W. Englemann
wavelengths of visible light
                               Red and blue light
                               most effective for
                               producing oxygen
                               during photosynthesis




    Wavelength and
                                Accessory
    photosynthesis              pigments




Chlorophyll in photosystems
  absorb light energy and
     release electrons         What happens
                                when light is
                               absorbed by a
                                 molecule?




                                    “Free” electrons are a source of kinetic energy




                                                                                      2
                              Z-scheme & energy flow




 Chemiosmosis drives ATP
        synthesis
                                    Photolysis and
                                    chemiosmosis




                            • Photolysis replaces electrons removed
                              from chlorophyll
                            • Electron flow “pumps” H+ ions through
                              membrane




Light reactions animation   Chemiosmosis animation




                                                                      3
          ATP synthase
       phosphorylates ADP
     (photophosphorylation)




                           H+ ions




           Chlorophyll                       When light energy is
                                            absorbed by chlorophyll
1.   Is the organelle in which
     photosynthesis takes place        1.   Chlorophyll produces oxygen
2.   Absorbs green wavelengths of      2.   Chlorophyll becomes an
     light
                                            accessory pigment
3.   Is the primary photosynthetic
     pigment                           3.   Chlorophyll is destroyed
4.   All of these                      4.   Chlorophyll becomes radioactive
5.   Both 1 and 2                      5.   Chlorophyll releases an electorn




Active transport of hydrogen                       Photolysis
ions into the thylakoid space          1.   Occurs when light energy splits a
                                            chlorophyll molecule in half
1.   Occurs during chemiosmosis        2.   Is when light splits open a chloroplast
                                            to release sugars
2.   Involves the electron transport   3.   Splits water molecules to resupply
     chain of photosystem II                chlorophyll with electrons
3.   Occurs by the process of          4.   Is the production of ATP utilizing a
                                            hydrogen ion gradient
     photolysis
                                       5.   Occurs when absorbed light causes
4.   Involves the electron transport        an electron to be removed from a
     chain of photosystem I                 chlorophyll molecule




                                                                                      4
       The hydrogen ion gradient
     inside the thylakoid membrane
           forms as a result of
1.    Photosystem II
2.    Photolysis
3.    Chemiosmosis
4.    Photophosphorylation
5.    Both 1 and 2




      Dr. Calvin, Nobel prize in     Calvin’s experiment (see Fig. 8.9)
           chemistry, 1961




     Calvin’s                              The Calvin cycle
     results                                produces G3P
                                     Occurs in the
                                     stroma
                                     Several enzyme-
                                     catalyzed steps
                                     Requires energy
                                     Produces sugars




                                                                          5
                               Summary of photosynthesis
Calvin Cycle Animation




Photosynthesis animation
                               Rate of photosynthesis varies
                               with environmental conditions


                               What is meant by the “rate of
                               photosynthesis”?

                               What environmental conditions
                               affect the rate of photosynthesis?




Factors influencing the rate   Variations of photosynthesis
    of photosynthesis
                                 85% of plants use “C3”
                                 photosynthesis
Carbon dioxide concentration     – C3 cycle = Calvin cycle
Water availability               C4 photosynthesis
                                 – C4 plants include many tropical
Light intensity                    monocots, other grasses (0.4% of
Temperature                        plants)
                                 Crassulacean Acid Metabolism
                                 (CAM)
                                 – CAM plants – cacti, orchids,
                                   bromeliads, succulents (~10% of
                                   plants)




                                                                      6
C4 photosynthesis is more   Photorespiration
 efficient than C3 under    and rubisco
    certain conditions
                            Rubisco – Ribulose 1,5-
                            bisphosphate
                            carboxylase/oxygenase
                             – Most abundant protein on earth
                               (25-40% of total plant protein)
                             – Activity depends on carbon
                               dioxide concentration in the leaf




Rubisco activity and CO2    When would photorespiration
     concentration               occur and why?

                            When are CO2 concentrations
                            low?
                                       –When stomata close
                                          •Hot days
                                          •Moisture stress




                                                                   7
                                                  Crassulacean Acid
           C4 vs. CAM                                Metabolism
                                            Evolved in areas of high light
                                            intensity, little precipitation
                                            Stomata closed during the day, open
                                            at night




Which of the following are                  The Calvin cycle occurs
true of the Calvin cycle?
                                       1.    In C3 plants but not C4 or
1.   Occurs in the cytoplasm
                                             CAM plants
2.   RUBP reacts with oxygen to form   2.    In the mesophyll of all plants
     Rubisco                           3.    In the bundle sheath of C4
3.   RUBP reacts with CO2 to form            plants
     Rubisco
4.   All of these are true             4.    In C4 and CAM plants, but not
5.   None of these are true                  C3 plants




                                                                                  8
     Photorespiration is
                                         During photorespiration
     most likely to occur
                                         1.    Plants react O2 with glucose to
1.    On cool, cloudy days                     make ATP
2.    In plants adapted to desert        2.    Plants react O2 with ATP to make
                                               glucose
      habitats
                                         3.    Plants use the energy of light to
3.    In C3 plants                             make ATP
4.    In C4 plants and CAM plants        4.    RUBP reacts with CO2 to make
                                               sugars
5.    Both 2 & 4
                                         5.    RUBP reacts with O2 to make CO2




                                              Photosynthesis research
            CAM plants
1.    Use their bundle sheath cells to        Why study photosynthesis?
      run the Calvin cycle at night
2.    Use their bundle sheath cells to
      run the Calvin cycle during the
      day
3.    Absorb CO2 during the day, and
      make sugars during the night
4.    Absorb CO2 during the night, and
      make sugars during the day
5.    Both 1 and 3                                        Photosynthesis Center at Arizona State




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