The Calvin Cycle

Overview

• The Calvin Cycle is the second set of reactions in photosynthesis.
• Known as light-independent or dark reactions since it doesn't require light directly.
• Needs ATP and NADPH from light-dependent reactions.
• Occurs in the stroma, the fluid surrounding the thylakoids.

Key Inputs and Roles

• ATP: Provides energy.
• NADPH: Provides electrons and hydrogen to reduce CO2 to sugars.

Phases of the Calvin Cycle

Phase 1: Carbon Fixation

• Enzyme rubisco adds CO2 to a 5-carbon compound RuBP.
• Forms a 6-carbon compound that splits into two 3-phosphoglycerates.
• Involves fixing three molecules of CO2.

Phase 2: Reduction

• ATP provides energy to form an intermediate compound.
• NADPH reduces the intermediate to form glyceraldehyde 3-phosphate (G3P).
• Net gain: 1 G3P for every 3 CO2 molecules.

Phase 3: Regeneration

• 1 G3P is used, 5 remain to regenerate RuBP.
• Requires energy from ATP to form three 5-carbon RuBP molecules.

Overall Process

• Cycle needs to repeat to synthesize glucose from 6 CO2 molecules.
• Produces G3P, with two needed to form one glucose molecule.

Importance

• Glucose and other organic compounds formed support plant growth and sustain life.
• Photosynthesis interactive can be explored at BioMan Biology to understand the process better.

Conclusion

• Calvin Cycle crucial for converting light energy into chemical energy stored as glucose.
• Light-dependent reactions provide necessary ATP and NADPH.

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