Biology20 Photosynthesis Light Independent Reaction

2 The Second Step stromaOccurs in the stroma notDoes not require light Calvin CycleAlso called the Calvin Cycle –Analyzed by a guy named Melvin Calvin This step uses CO 2 and H to form sugar!! –CO 2 comes from the atmosphere –H comes from NADPH of the Light Dependent Reaction Originally came from water –Energy to drive this cycle is supplied by ATP from the Light Dependent Reaction.

3 Steps in the Calvin Cycle CARfixedRuBP 1) CARbon dioxide is fixed by RuBP –“Fixed” = to be incorporated into an organic molecule –RuBP = Ribulose Biphosphate a 5 carbon sugar acts as a CO 2 acceptor RuBP + CO 2 = C 6 sugar –This sugar is very unstable and immediately splits into two C 3 sugars called PGA PGA = phosphoglyceric acid

4 Step 1

5 Step 2 PGALPGA uses ATP as an energy source to remove hydrogen from NADPH to form a new molecule called PGAL –PGAL = phosphoglyceraldehyde –PGAL = C 3

6 Step 2

7 Fates of PGAL 1) In 6 Calvin Cycles, 12 PGAL’s (C 3 ) are formed. –2 are used to produce C 6 H 12 O 6 –10 are used to recycle into RuBP 2) PGAL can be used as an energy source in cell respiration 3) PGAL can be modified to produce fat or protein.

Let’s Draw

9 [6] PGA (C 3 ) Light Dependent Reaction RuBP [6] C 6 Sugars 6 CO 2 Protein Formation Lipid Formation Cellular Respiration [12] PGAL (C 3 )

10 [6] PGA (C 3 ) Light Dependent Reaction [6]RuBP [6] C 6 Sugars 6 CO 2 Protein Formation Lipid Formation Cellular Respiration [12] PGAL (C 3 )

Now that you’re smarter... Questions p. 195 Review what you’ve learned by… completing your photosynthesis review sheet and completing your unit objectives handout