Light Reaction and Dark Reaction

Overview of Photosynthesis

• Photosynthesis is a process that converts light energy into chemical energy.
• Occurs in chloroplasts via two phases:
  • Light Reaction: Light-dependent process.
  • Dark Reaction: Light-independent process, also known as the biosynthetic phase.

Light Reaction

• Definition: A light-dependent process crucial for photosynthesis.
• Key Events:
  • Light absorption by chlorophyll within thylakoids.
  • Hydrolysis of water occurs, releasing oxygen.
  • Formation of ATP and NADPH.
• Photosystems:
  • Photosystem I (PS-I): Absorbs light at 700 nm.
  • Photosystem II (PS-II): Absorbs light at 680 nm.
• Process:
  • Occurs in thylakoids of chloroplasts.
  • Excitation of chlorophyll-a leads to energy production (ATP & NADPH).

Dark Reaction

• Definition: Also known as carbon-fixing reaction.
• Characteristics:
  • Light-independent process.
  • Utilizes products (ATP, NADPH) from the light reaction.
• Location: Occurs in the stroma of the chloroplast.
• Calvin Cycle:
  • Captures CO2 through stomata.
  • Converts CO2 into glucose using ATP and NADPH.

Differences between Light and Dark Reactions

FAQs

• Light Reaction:
  • Takes place in thylakoid membranes.
  • Light absorbed to generate NADPH and drive protons for ATP production.
• Dark Reaction:
  • Uses CO2 with ATP and NADPH to produce glucose.
  • Takes place in chloroplast stroma.
• End Products:
  • Light Reaction: ATP and NADPH.
  • Dark Reaction: Glucose.
• Timing:
  • Dark reaction occurs during the day but does not require direct light.

Additional Information

• Plant Energy without Light: ATP produced from other sources, anaerobic photosynthetic bacteria.
• Impact of Light: Provides energy for growth through photosynthesis.