Photosynthesis: Light Dependent Reactions

Overview of Photosynthesis

• Process by which plants, algae, and some bacteria convert light energy from the sun into chemical energy in the form of organic compounds (e.g., glucose)
• Essential for life on Earth, as it provides energy and organic compounds for the food chain

Light-Dependent Reactions

• Occur in the thylakoid membranes of the chloroplast
• Light energy is absorbed by pigments such as chlorophyll and converted into ATP and NADPH
• Two stages:
  • Light absorption: Light energy is absorbed by pigments, exciting electrons
  • Electron transport: Electrons are passed through a series of electron carriers, generating ATP and NADPH

Light-Independent Reactions (Calvin Cycle)

• Occur in the stroma of the chloroplast
• Use ATP and NADPH produced in the light-dependent reactions to convert CO2 into glucose
• Three stages:
  • Carbon fixation: CO2 is fixed into a 3-carbon molecule using the enzyme RuBisCO
  • Reduction: 3-carbon molecules are reduced to form glyceraldehyde 3-phosphate (G3P)
  • Regeneration: G3P is converted back into RuBP, allowing the cycle to continue

Factors Affecting Photosynthesis

• Light intensity: Increased light intensity can increase photosynthesis, but excessive light can lead to photoinhibition
• Temperature: Optimal temperature for photosynthesis varies between species, but generally ranges from 20-30°C
• Water availability: Drought can limit photosynthesis, while excessive water can lead to flooding and reduced photosynthesis
• CO2 concentration: Increased CO2 concentration can enhance photosynthesis

Importance of Photosynthesis

• Provides energy and organic compounds for the food chain
• Supports life on Earth
• Influences climate and atmospheric CO2 levels