Photosynthesis + water + energy  glucose + oxygen carbon dioxide 6CO 2 6H 2 O C 6 H 12 O 6 6O 2 light energy  +++ Reactants Products

Review: Light reactions Convert solar energy to chemical energy –ATP –NADPH What can we do now?  energy  electron donator   build stuff !! photosynthesis ATP

The second phase of photosynthesis is called the Calvin Cycle (Light-Independent phase) LIGHT-DEPENDENT PHASE (Requires Sunlight) LIGHT-INDEPENDENT PHASE (Does Not Require Sunlight) REMEMBER: This is when the chemical energy produced in the first phase is combine with Carbon Dioxide to create sugar.

LIGHT-INDEPENDENT REACTIONS/ Calvin Cycle SUGAR ASSEMBLY- SECOND PHASE The light-INDEPENDENT reactions (or Calvin cycle) use the chemical energy produced in the light-dependent reactions (ATP and NADPH) and carbon dioxide to create sugar.

5 The Calvin Cycle

STROMA (Fluid interior) The Calvin Cycle takes place in the stroma of the chloroplast.

Carbon Dioxide enters the plant leaf through openings called stomata.

THE CALVIN CYCLE At the beginning of the Calvin Cycle, six CO 2 molecules bond with six 5-carbon sugar called RuBP (Ribulose Biphosphate) to form an six unstable 6-carbon sugar. ( An enzyme called Rubisco is responsible for joining these molecules.) CCCCC C O O CARBON DIOXIDE RuBP CCCCC CCCCCC UNSTABLE 6-CARBON SUGAR

THE CALVIN CYCLE This step is called Carbon Fixation, because a carbon is “fixed” onto the RuBP. CCCCC C O O CARBON DIOXIDE RuBP CCCCC CCCCCC UNSTABLE 6-CARBON SUGAR

Section 9.2 Summary – pages (CO2) (RuPB) THE CALVIN CYCLE 6 carbon sugar

THE CALVIN CYCLE CCCCCC UNSTABLE 6-CARBON SUGAR CCC CCC The unstable 6-carbon sugars immediately split to form twelve stable 3-carbon molecules. These molecules are called PGA’s (phosphoglycerate) PGAs

Section 9.2 Summary – pages (CO2) (PGA) (RuPB) THE CALVIN CYCLE 6 Carbon sugar 3 Carbon molecules

THE CALVIN CYCLE 12 NADPH and 12 ATP (from the light dependent reactions) then give their energy to turn the 3- carbon PGA molecules into PGALs (3-carbon sugars called glyceride tri-phosphate with higher energy bonds). CCC CCC CCC CCC 2 PGAL molecules NADPHATP ADP + NADP + ADP, P, and NADP+ are released and then return to the thylakoid membrane to be re-energized.

Section 9.2 Summary – pages (CO2) ATP ADP + NADPH NADP + (PGAL) (PGA) (RuPB) THE CALVIN CYCLE 6 carbon sugar 3 carbon molecules

Section 9.2 Summary – pages (CO2) ATP ADP + NADPH NADP + (PGAL) (PGA) (RuPB) 6 carbon sugar 3 carbon molecules (2 PGAL) (Sugar) 2 PGALs are transferred out of the chloroplast to the cytoplasm of the cell where they are combined to make a six-carbon glucose.

Section 9.2 Summary – pages (CO2) ATP ADP + (Sugar) NADPH NADP + (PGAL) ATP (RuPB) 6 carbon sugar 3 carbon molecules The ten remaining PGAL molecules each with 3-carbon atoms, reorganize using 6 ATP molecules to make 6 molecules of RuBP (the 5-carbon sugar) to start the cycle all over again.

Section 1 Check Question 3 A molecule of adenosine that has two phosphate groups bonded to it is ______. A. AMP B. ADP C. ATP D. ACP

Section 1 Check The answer is B. ADP is adenosine diphosphate. Adenosine PPP P P PP Adenosine triphosphate (ATP) Adenosine diphosphate (ADP)

Section 1 Check Question 4 What is the function of the protein molecule shown in this diagram? ATP ADP Protein P Energy

Section 1 Check This protein molecule has a specific binding site for ATP. In order to access the energy stored ATP, the protein molecule binds the ATP and uncouples one phosphate group. This action releases energy that is then available to the cell. ATP ADP Protein P Energy

Section 2 Check The function accomplished by the light-dependent reactions is ________. Question 6 D. conversion of sugar to PGAL C. carbon fixation B. sugar production A. energy production

Section 2 Check The answer is A. The light-dependent reactions transfer energy from the sun to chlorophyll, and pass energized electrons to proteins embedded in the thylakoid membrane for storage in ATP and NADPH molecules. Sun Chlorophyll passes energy down through the electron transport chain. for the use in light-independent reactions bonds P to ADP forming ATP oxygen released splits H 2 O H+H+ NADP + NADPH Light energy transfers to chlorophyll. Energized electrons provide energy that

Section 2 Check The first step in the Calvin cycle is the ________. Question 7 D. Bonding of carbon dioxide to RuBP C. Splitting of six-carbon sugar into two three-carbon molecules B. production of PGAL A. replenishing of RuBP

Section 2 Check The answer is D. The carbon atom from CO 2 bonds with a five-carbon sugar to form an unstable six-carbon sugar. This molecule then splits to form two three-carbon molecules.

25 Photosynthesis Overview copyright cmassengale