Download SBI4U Light Independent Reactions

2017-02-07
Cyclic Electron Pathway
Cyclic Electron Pathway
! Occurs in some photosynthetic bacteria and
plants
! P700 (PS I) may operate alone, without
interacting with P680 (PS-II)
! produces ATP, but does NOT produce
NADPH
! The electrons return back to P700.
Light-Independent Reactions:
The Calvin Cycle
! Occurs in 80% of plants
! Synthesis reactions that occur in the stroma
! CO2 + ATP + NADPH → Glucose
Light-Independent Reactions:
The Calvin Cycle
! No light required but typically occurs during the
day
! To produce glucose: it takes 6 turns and uses
18 ATP and 12 NADPH
"  Carbon dioxide – comes into the leaf via
stomata
"  ATP and NADPH – from the light-dependent
rxns
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Key Terms
RuBP - ribulose 1,5-biphosphate
PGA - 3-phosphoglycerate
G3P - glyceraldehyde 3-phosphate
Three Stages of Calvin Cycle
1. Carbon Fixation
2.  Carbon
Reduction
3. Regeneration of
RuBP
The Calvin Cycle
Phase 1: Carbon Fixation
! 3 CO2 are added to 3 RuBP (5C) to form 3
unstable 6-carbon intermediates.
! The intermediates split into six 3-carbon
molecules called PGA.
! These reactions are catalyzed by rubisco
(ribulose biphosphate carboxylase/
oxygenase)
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The Calvin Cycle
Phase 2: Reduction Reactions
! 6 PGAs are phosphorylated by 6 ATPs to
form 6 molecules of 1, 3-BPG.
! 6 NADPH molecules reduce the six 1,3BPG to 6 G3P or PGAL.
! One molecule of G3P exits the cycle as a
final product.
The Calvin Cycle
Phase 3: Regeneration of RuBP
! 3 ATP are used to rearrange the
remaining 5 G3P into 3 molecules of
RuBP (5 carbons).
! The cycle continues with the RuBP fixing
more CO2.
Homework
! complete Calvin Cycle worksheet
!  read pg. 179-181
!  pg. 182 #1-5
Photosynthesis Test
Wed. February 15
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