Transcript Photsynthesis III - Light Indpendent

AP Biology
Light Independent Reactions – Calvin
Cycle
Photosynthesis Light Reaction
Photosynthesis Calvin Cycle
Calvin Cycle step 1
Carbon Fixation
• Part 1 of the Calvin Cycle:
– 3 Carbon Dioxides enter the cycle and combine
with RuBP to create 3 very unstable 6 carbon
molecules.
– These 6-carbon molecules instantly break down
into 6, 3-carbon molecules that are much more
stable.
– We now have all of the carbons in the cycle that
are needed to make ½ of a glucose molecule.
Calvin Cycle step 2
Reduction
• Part 2 of the Calvin Cycle:
– ATP and NADPH are now used to modify the
original 3-carbon molecules in preparation for one
of them to leave the cycle to make glucose.
– This stage is called reduction because electrons
are added to the 3-carbon molecules to transform
them into the building blocks for glucose.
– ADP and NADP+ are sent back to the ETC.
Calvin Cycle step 3
Regeneration of Carbon Dioxide
Acceptor
• Part 3 of the Calvin Cycle:
– The remaining 3-carbon molecules are further
modified using ATP to get back to the starting
material in the cycle.
– If you trace the number of carbons through the
cycle, you should end up with the same amount
that you started with.
– The cycle starts with 15 carbons and at the end of
the third phase you should have 15 carbons.
– What happens if the plant has no carbon dioxide?
Calvin Cycle Intermediates
C4 Plants and
Photorespiration
Photosynthetic
cells of C4 plant
leaf
Mesophyll
cell
PEP carboxylase
Mesophyll cell
CO2
Bundlesheath
cell
The C4 pathway
Oxaloacetate (4 C) PEP (3 C)
Vein
(vascular tissue)
ADP
Malate (4 C)
ATP
C4 leaf anatomy
Stoma
Bundlesheath
cell
Pyruvate (3 C)
CO2
CALVIN
CYCLE
Sugar
Vascular
tissue
CAM Plants and
Photorespiration
Sugarcane
Pineapple
CAM
C4
CO2
Mesophyll
cell
Organic acid
Bundlesheath
cell
CO2
CO2 incorporated
into four-carbon Organic acid
organic acids
(carbon fixation)
CO2
CALVIN
CYCLE
Sugar
Spatial separation of steps
CO2
Organic acids
release CO2 to
Calvin cycle
Night
Day
CALVIN
CYCLE
Sugar
Temporal separation of steps
Stomata of Leaves & Transpiration