**Photosynthesis** is the process plants, algae, and some bacteria use to convert light energy into chemical energy stored in sugar.
### Overall equation
\[
6CO_2 + 6H_2O + \text{light energy} \rightarrow C_6H_{12}O_6 + 6O_2
\]
In words:
**carbon dioxide + water + light → glucose + oxygen**
### Where it happens
In plants, photosynthesis occurs mainly in leaf cells inside structures called **chloroplasts**. Chloroplasts contain **chlorophyll**, the green pigment that absorbs light—especially red and blue wavelengths.
### The two main stages
1. **Light-dependent reactions**
- Occur in the chloroplast’s thylakoid membranes.
- Chlorophyll absorbs sunlight.
- Water molecules are split, releasing **oxygen**.
- Light energy is stored in temporary energy-carrying molecules called **ATP** and **NADPH**.
2. **The Calvin cycle**
- Occurs in the fluid-filled stroma of the chloroplast.
- Uses ATP and NADPH to turn carbon dioxide into small sugar molecules.
- These molecules can be used to make **glucose**, which provides energy and materials for plant growth.
### Why photosynthesis matters
Photosynthesis:
- Produces most of the oxygen in Earth’s atmosphere.
- Removes carbon dioxide from the air.
- Provides the chemical energy that supports nearly all food chains.
- Stores solar energy in a form living organisms can use.
One important detail: plants also perform **cellular respiration**, using glucose and oxygen to release usable energy—just as animals do.