Photosynthesis Review - Khan Academy

Key Concepts

• Photosynthesis: Conversion of light energy to chemical energy (sugars) by plants, algae, and some bacteria.
• Photoautotrophs: Organisms that produce food using light energy.
• ATP (Adenosine Triphosphate): Energy carrier in living things.
• Chloroplasts: Site of photosynthesis in plant cells.
• Thylakoids: Structures within chloroplasts that absorb light.
• Grana: Stacks of thylakoids.
• Chlorophyll: Pigment that absorbs light energy for carbohydrate production.
• Stroma: Fluid surrounding grana in chloroplasts.

Photosynthesis Reaction

• Equation: Sunlight + CO₂ + H₂O → Glucose (C₆H₁₂O₆) + O₂
  • Solar energy is converted to chemical energy (glucose).
  • Oxygen is released as a byproduct.

Stages of Photosynthesis

1. Light-dependent Reactions

   • Location: Thylakoid membrane
   • Events: Capture light energy, stored as ATP
   • Requires Sunlight: Yes

2. Calvin Cycle

   • Location: Stroma
   • Events: ATP used to produce sugars
   • Requires Sunlight: No

Common Mistakes and Misconceptions

• Photosynthesis vs Cellular Respiration:
  • Opposite processes but not simple reversals.
  • Each has unique series of steps.
• Chlorophyll and Green Light:
  • Chlorophyll reflects green light (not absorbs).

Discussion Highlights

• NADPH: Electron carrier in photosynthesis.
• ATP and Sugar: ATP itself is not sugar; used in processes to create sugars from CO₂.
• Seasonal Photosynthesis: Deciduous trees store energy for winter dormancy; evergreens have adaptations to survive cold.

These notes provide a concise overview of photosynthesis, detailing key terms, stages, and common misconceptions, which are crucial for understanding how photosynthesis sustains life on Earth.