Photosynthesis

Photosynthesis

1. C3 (advantageous when weather is moderate)

   • - Uses RuBP Carboxylase to fix CO2 to RuBP in mesophyll cells.
     • O2 rises (stomata closes during hot weather)
       • RuBP carboxylase combines O2 with RuBP instead of CO2
         • Release 1 molecule of 3PG and CO2
           • PHOTORESPIRATION, CO2 is not delivered to the Calvin Cycle
   • -contains well-formed chloroplasts -arranged in parallel layers

2. C4 (an adaptation to avoid PHOTORESPIRATION during hot and dry weathers)

   • -bundle of sheath cells & mesophyll cells contain chloroplast -arrnged concentrically around the bundle sheath cells
   • -fixes CO2 to PEP, a C3 molecule. using the enzyme PEP carboxylase.
     • CAM (water containing plants)
       • minimal photosynthesis
       • occurs at night (stomata opens at night)
     • oxaloacetate
       • Malate (a reduced form of oxaloacetate) combines with CO2 and later pumped into bundle sheath cells (where CO2 enters the Calvin Cycle)
         • PHOTORESPIRATION does not occur. PEPCase does not combine with O2
           • Even when stomata is closed, CO2 is delivered to the Calvin Cycle.

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