Photosynthesis

Photosynthesis

1. Occurs in chloroplasts

   • Chloroplasts contain
     • Their own DNA
     • Their own ribosomes
     • Starch grains

2. Two Stages

   • 1 - Light dependent
     • Thylakoid membrane of Grana
       • Requires light and water
     • Inputs and Outputs
       • Inputs: H2O, NADP and ADP+Pi
       • Outputs: O2 NADPH, ATP
     • Light energy is used to split H2O into O, H+ and free -e
     • O2 released as waste
     • Electrons pass along a chain of molecules giving energy at each step (ETC)
     • -e Energy is used to make ATP
     • H+ joins NADP+ to make NADPH
   • 2- Light independent (Calvin Cycle)
     • Inputs and Outputs
       • Outputs: Glucose, NADP , ADP+Pi
       • Inputs: CO2, NADPH, ATP
     • Occurs in STROMA of Chloroplast. Depends on Stage 1.
     • Inorganic C needs to be converted to Organic C
       • SO RuBisCo does this, by bringing a C molecule from a CO2 molecule to a 5-C molecule in the stroma (Rubp)
         • Adding the C onto Rubp to make a 6-C molecule makes everything unstable
           • So the 6-C molecule breaks giving 2 x 3-Carbon molecule (3-Phosphoclycerate)
             • So now, we need energy. ATP puts phosphate onto our 3 C molecule and NADPH pops some electrons on
               • So we have a high energy 3-C molecule (G3P) that can be converted to almost any carb
                 • Some G3P leaves the cycle and Glucose is formed from it and some is recycled back to Rubp to continue the CYCLE.

3. Factors Affecting Photosynthesis

   • Light
     • Availability affects rate
       • Lower light = fewer products
     • Wavelength (Wl) and Intensity affect rate too
       • Wl absorbed - depends on Chlorophyll and accessory pigments
       • At the same Wl, P/s rate will increase until limited by some other factor
   • Temperature
     • Affects photosynthesis same way it affects all enzymes
     • High temp, high rate of P/s
   • CO2
     • Atmospheric CO2 or that from Cellular respiration
     • Low CO2 = Low P/S rates, because limits Calvin cycle
   • Water
     • Reduction in H2O = reduce in P/S rate because
       • Needed as a reactant in Stage 1
       • Stomata will close, reducing CO2 levels
       • Reduces availability of active sites

4. Chemosynthesis

   • Some organisms use chemicals instead of light to produce the organic molecules required for life