What is photosynthesis, and how does it work?

Photosynthesis is the process by which green plants, algae, and some bacteria use sunlight, water, and carbon dioxide to produce glucose (food) and release oxygen as a byproduct. It is the foundation of almost all food chains on Earth.

The overall equation:

6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂
Carbon dioxide + Water + Sunlight → Glucose + Oxygen

Where it happens: In the chloroplasts of plant cells, using chlorophyll (the green pigment) to capture light energy.

The two stages:

Stage 1 — Light-dependent reactions (in thylakoid membranes):

• Chlorophyll absorbs sunlight (mainly red and blue wavelengths)
• Water molecules are split: 2H₂O → 4H⁺ + 4e⁻ + O₂
• Oxygen is released — this is the oxygen we breathe
• Energy stored as ATP and NADPH (energy carriers)

Stage 2 — Calvin Cycle, Light-independent reactions (in the stroma):

• CO₂ from air is "fixed" (attached) to organic molecules
• ATP and NADPH from Stage 1 drive conversion of CO₂ into glucose
• No direct sunlight required for this stage

Factors affecting photosynthesis rate: Light intensity, CO₂ concentration, temperature (optimal 25–35°C), water availability