Photosynthesis
Summary: Photosynthesis is the chemical reaction by which plants produce glucose and oxygen from carbon dioxide and water, using light energy absorbed by chlorophyll. Word equation: carbon dioxide + water → glucose + oxygen. Symbol equation: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. Tags: igcse chemistry definition environmental-chem Created: 2026-07-14 Last Updated: 2026-07-23
Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy into chemical energy, producing glucose and oxygen from carbon dioxide and water.
The Reaction
Word Equation
Carbon dioxide + Water → Glucose + Oxygen
(In the presence of chlorophyll and using energy from light)
Symbol Equation
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
(In the presence of chlorophyll and light)
Conditions Required
| Requirement | Role |
|---|---|
| Carbon dioxide (CO₂) | Reactant — taken in from the air through stomata |
| Water (H₂O) | Reactant — absorbed from the soil through roots |
| Chlorophyll | Green pigment that absorbs light energy; acts as a biological catalyst |
| Light energy | Energy source that drives the reaction (endothermic) |
Why Is Photosynthesis Important?
- Produces oxygen — essential for respiration of most living organisms
- Removes CO₂ from the atmosphere — helps regulate the Earth’s carbon cycle and climate
- Produces glucose — the primary energy source for plants and the basis of food chains
- Fossil fuel origin — fossil fuels (coal, oil, natural gas) are derived from ancient photosynthesising organisms
Photosynthesis and the Environment
Photosynthesis is relevant to IGCSE Chemistry in the context of:
- Air quality and climate (Topic 10.3) — plants remove CO₂ from the atmosphere
- Carbon cycle — photosynthesis is a key carbon sink
- Climate change strategies — planting trees increases CO₂ removal
Photosynthesis vs Combustion
Photosynthesis is essentially the reverse of combustion:
| Photosynthesis | Combustion | |
|---|---|---|
| Equation | 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ | C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O |
| Energy | Absorbs energy (endothermic) | Releases energy (exothermic) |
| CO₂ | Consumed | Produced |
| O₂ | Produced | Consumed |
Key Facts
- Word equation: carbon dioxide + water → glucose + oxygen
- Symbol equation: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
- Requires: chlorophyll and light energy
- Takes place in the chloroplasts of plant cells
- Removes CO₂ from the atmosphere and produces O₂
- Planting trees is a strategy to reduce atmospheric CO₂ and combat climate change
See Also
- Climate Change and Greenhouse Gases
- Composition of Air
- Carbon Dioxide (CO2)
- Oxygen (O2)
- IGCSE-Chem-Index
This is a key term definition page — part of the IGCSE Chemistry (0620/0971) keyword glossary.