Photosynthesis Overview Class

Photosynthesis Overview

• Photosynthesis is a biological process where green plants, algae, and some bacteria convert light energy into chemical energy stored in glucose inside chloroplasts.

Photosynthesis Equation

• Word Equation: Carbon dioxide + Water → Glucose + Oxygen (in the presence of sunlight and chlorophyll)
• Chemical Equation: (Note: No chemical equation provided in the text)

Key Concepts

• Autotrophs: Organisms like plants and algae that produce their own food via photosynthesis.
• Energy Conversion: Light energy is converted into chemical energy stored in glucose.
• Pigments: Chlorophyll (absorbs red and blue light, reflects green) is the primary pigment, while accessory pigments like carotenoids and xanthophylls also participate.
• Organelles: Chloroplasts are the site of photosynthesis, with specific areas involved in each stage:
  • Thylakoid membranes: Light-dependent reactions.
  • Stroma: Light-independent reactions (Calvin Cycle).

Stages of Photosynthesis

Light-Dependent Reactions (Photo Phase)

• Location: Thylakoid membranes.
• Inputs: Light energy, water, ADP, and NADP+.
• Outputs: Oxygen, ATP, and NADPH.
• Key Processes:
  • Photon absorption by chlorophyll initiates the process.
  • Photolysis splits water molecules into oxygen, electrons, and hydrogen ions.
  • The Electron Transport Chain (ETC) uses energized electrons to make ATP and NADPH.

Light-Independent Reactions (Calvin Cycle/Dark Phase)

• Location: Stroma
• Inputs: Carbon dioxide, ATP, and NADPH.
• Outputs: Glucose, ADP, and NADP+.
• Key Steps:
  • Carbon fixation: Carbon dioxide combines with a 5-carbon molecule (RuBP) using the enzyme Rubisco.
  • Reduction: ATP and NADPH reduce intermediate molecules forming G3P (glyceraldehyde-3-phosphate).
  • Regeneration: RuBP is regenerated for the cycle to continue.

Factors Affecting Photosynthesis

• Light Intensity: Increases the rate up to a saturation point, beyond which the rate plateaus.
• Carbon Dioxide Concentration: Higher levels lead to increased rates until other factors become limited.
• Temperature: Enzymes function optimally in specific temperatures (around 25–30°C in most plants). Extreme temperatures lower photosynthesis rate.
• Water Availability: Water scarcity slows photosynthesis and causes stomata closure, reducing carbon dioxide uptake.
• Chlorophyll levels: Healthy chlorophyll is essential for efficient light absorption.

Significance of Photosynthesis

• Oxygen Source: Photosynthesis produces oxygen, vital for life on Earth.
• Energy for Life: Photosynthesis forms the base of most food chains by producing glucose.
• Carbon Cycle: Removes carbon dioxide from the atmosphere, converting it into organic molecules.
• Global Importance: Balances atmospheric gases, and plays a crucial role in reducing the "greenhouse effect."

Photosynthesis vs. Cellular Respiration (Comparison)

Real-Life Applications

• Agriculture: Optimizing factors like light, water, and CO2 can enhance crop yields.
• Global Carbon Balance: Forests are significant carbon sinks due to their photosynthesis processes.
• Biofuels: Some plants, like algae, use photosynthesis to create biomass for renewable energy.
• Artificial Photosynthesis: Researchers strive to replicate photosynthesis for sustainable energy production.