Overview of Photosynthesis

Overview of Photosynthesis

• Photosynthesis is the process by which green plants and some other organisms use sunlight to synthesize foods from carbon dioxide and water.
• It's vital for life on Earth, as it's the primary source of oxygen and most organic compounds used by living organisms.
• Photosynthesis takes place in chloroplasts, containing chlorophyll, a green pigment absorbing light energy.

Stages of Photosynthesis

• Photosynthesis occurs in two main stages: light-dependent and light-independent reactions (Calvin cycle).
  • Light-dependent reactions: These reactions require light energy.
    • Light energy excites electrons in chlorophyll molecules.
    • Excited electrons move along an electron transport chain, generating ATP and NADPH.
    • Water is split, releasing oxygen and replacing lost electrons.
  • Light-independent reactions (Calvin cycle): These reactions don't directly require light.
    • Carbon dioxide from the atmosphere is incorporated into organic molecules, primarily sugars.
    • Enzyme RuBisCO catalyzes carbon fixation.
    • ATP and NADPH provide energy and reducing power for converting carbon dioxide into sugars.

Factors Affecting Photosynthesis

• Environmental factors influence photosynthesis rate.
  • Light intensity: Increases rate up to a saturation point.
  • Carbon dioxide concentration: Higher concentrations increase rate to a saturation point.
  • Temperature: Photosynthesis has an optimal temperature range; deviations decrease the rate.
  • Water availability: Crucial; water shortage closes stomata, reducing carbon dioxide uptake and hindering photosynthesis.
  • Chlorophyll concentration: Higher levels increase light absorption and potentially increase rate to a point of diminishing returns.

Products of Photosynthesis

• The primary products are glucose (a sugar) and oxygen.
• Glucose fuels plant growth and other metabolic processes.
• Oxygen is released into the atmosphere.

Importance of Photosynthesis

• Oxygen production: Photosynthesis is the main source of atmospheric oxygen.
• Food source: Forms the base of most food chains, fueling nearly all life.
• Carbon dioxide removal: Regulates atmospheric carbon dioxide, contributing to climate stability.
• Raw material source: Organic compounds are used by organisms for growth and maintenance.

C3, C4, and CAM Photosynthesis

• Different photosynthetic pathways exist, adapting to different environments.
  • C3 photosynthesis: The most common pathway, less efficient in high temperatures and drought.
  • C4 photosynthesis: Adapted to hot, dry conditions, minimizing photorespiration and maximizing carbon fixation.
  • CAM (Crassulacean Acid Metabolism) photosynthesis: Conserves water by opening stomata at night to take in carbon dioxide, storing it for use during the day. Common in desert plants.