Energy Production in Plants: Calvin Cycle and Photosynthesis

Overview

• Energy in cereals like wheat or corn comes from sugars made by plants.
• Carbon is the chemical backbone found in carbon dioxide (CO2) from the air.
• Photosynthesis is the process that turns CO2 into glucose.

Photosynthesis

• Divided into two steps:
  1. Light-dependent reactions: Stores energy from the sun in the form of ATP.
  2. Calvin Cycle: Converts carbon into sugar.

The Calvin Cycle

• Known as nature's sustainable production line.
• Starting Materials:
  • CO2 molecules from the air.
  • Ribulose biphosphate (RuBP) with five carbons.
• Key Enzyme:
  • Rubisco: Combines one carbon from CO2 with RuBP.
• Intermediate Products:
  • A six-carbon sequence splits into phosphoglycerates (PGAs) with three carbons each.

Energy and Chemical Inputs

• ATP: Provides energy.
• NADPH: Adds hydrogen to PGA chains, forming glyceraldehyde 3-phosphate (G3P).

Glucose Formation

• Glucose requires six carbons, from two G3P molecules.
• The Calvin cycle operates simultaneously on multiple production lines to efficiently produce sugar.
  • Six production lines create 36 carbons in total.
  • 12 G3P molecules are formed; 2 are used to form glucose.

Recreating RuBP

• Essential for cycle continuity:
  • 10 G3P molecules are used to regenerate RuBP chains.
  • Molecular transformations ensure no wastage.
• Process:
  • G3P molecules combine to form RuBP by creating carbon chains of different lengths.

Importance of Cycles in Nature

• Cycles provide efficiency and sustainability by reusing and rebuilding ingredients.
• Feedback loops maximize use of available resources like sunlight and carbon.
• Cycles support continuous production and energy provision in nature.