The Calvin Cycle The Calvin Cycle is a circular process that regenerates the starting molecule at the end of the cycle. It is an anabolic process consuming energy to produce a sugar molecule.

Calvin Cycle Calvin Cycle - 3 cycles are required to produce 1 3 carbon sugar (G3P) Carbon fixation – 3 CO 2 molecules are incorporated 1 at a time by the enzyme rubisco – the product immediately splits into two 3 carbon sugars, 3-phosphoglycerate Energy requirements – ATP is used to generate intermediate products – Each NADPH donates 2 e- to energize the bonds of the intermediate product G3P G3P is the same molecule produced in the 1st stage of gylcolysis (1 st step in cellular respiration) Regeneration of RuBP (Starting Molecule)

Summary Consumed (used) – 9 ATP – 6 NADPH – 3 CO 2 Produced – 1 G3P (through 3 cycles)  G = 114kcal/mol 6CO2 + 18ATP + 12 NADPH + 12H 2 O  C 6 H 12 O ADP + 18Pi + 12NADP H + + 6O 2 + 6H 2 O Note that the product is not glucose, fructose, or sucrose. Another step is required to fuse 2 G3P to form a 6 carbon sugar. – This process takes 6 turns of the cycle! – Glucose is formed from the fusion of 2 molecules of G3P

Factors Affecting Photosynthesis Water – Lack of water slows or even stops the photosynthesis process Strategies… – waxy cuticle – Storage of water – Closing of stomata (openings in the leave where gas enters and leaves) during times when water loss would be excessive

Factors Affecting Photosynthesis Solar radiation (insolation) – Too much or too little insolation Chlorophyll operate between 0 o C and 35 o C Strategies – Deciduous plants (annuals) … lose leaves in fall and winter » Conserves energy and resources – Store CO2 and ATP for conversion at times when temperatures are not excessive » Plant opens stomata at night to reduce water loss » Uses O 2 produced to synthesize CO 2 from organic tissues