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This overview of photosynthesis focuses on the Calvin Cycle (C3 pathway) and its crucial role in converting CO2 into sugars using ATP and NADPH. The cycle involves key components like RuBP, Rubisco, and G3P. Additionally, it discusses photorespiration challenges in arid conditions when O2 accumulates and CO2 depletes, affecting carbon fixation. The C4 and CAM pathways present innovative solutions to these challenges. C4 separates carbon fixation spatially, while CAM offers temporal separation, optimizing photosynthesis under varying environmental conditions.
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Photosynthesis Photosynthesis Dark Reactions
Calvin Cycle (C3 Pathway) 6ATP + 6NADPH + 3 RuBP + 3 CO2 6 G3P 3 ATP + 5 G3P 1 G3P Ready for cell use
Calvin Cycle 3 – CO2 5C 5C 1C 3 – RuBP (Ribulose Bisphophate) 3 – RuBP 3C 6 ATP Rubisco 6 - PGA C3 Pathway 3C 5 – G3P 6 – G3P 3 ATP 1 – G3P 6 NADPH
Calvin Cycle 3 – CO2 5C 5C 1C 3 – RuBP 3 – RuBP 3C 6 ATP Rubisco 6 - PGA C3 Pathway 3C 6 – G3P 5 – G3P 3C 3 ATP 1 – G3P 2 – G3P 6 NADPH
Photorespiration • In arid conditions… • stomata close • O2 builds up • CO2 is depleted • Rubiscolinks RuBP to O2 • No carbon fixation • No sugars
C4 Pathway – PR Solution 1 Mesophyll Cell O2 ATP Bundle Sheath Cell Calvin Cycle Vascular Tissue CO2 • CO2 fixing enzyme has minimal O2 affinity • 4-C molecule forms (C4 Pathway) • Spatial separation of Calvin cycle (rubisco) and O2 3C 4C 3C CO2 Rubisco works here Sugar
CAM Pathway – PR Solution 2 • Temporal separation of carbon fixation & Calvin cycle • Stomata open at night to collect CO2 (minimal evap.) • Fixed CO2kept until ATP & NADPH available during day
