### What is photosynthesis?
Photosynthesis is how plants, algae, and some bacteria use light energy to make food (glucose) from carbon dioxide and water. It also releases oxygen into the air.

### Where it happens
- **Chloroplasts**: tiny green structures in plant cells.
- **Chlorophyll**: the green pigment that captures light.

### Two main stages
1) **Light-dependent reactions** (in the thylakoid membranes)
- Light energy splits water into oxygen, protons, and electrons.
- **Outputs**: oxygen (O2), and energy carriers called **ATP** and **NADPH**.

2) **Calvin cycle / light-independent reactions** (in the stroma)
- Uses ATP and NADPH to turn **carbon dioxide (CO2)** into **glucose (C6H12O6)**.
- Key idea: carbon fixation (enzyme: Rubisco).

### Overall equation
\(\text{6 CO}_2 + \text{6 H}_2\text{O} + \text{light energy} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + \text{6 O}_2\)

### Why it matters
- **Food**: creates sugars that fuel plant growth (and the organisms that eat plants).
- **Oxygen**: supplies the O2 we breathe.
- **Climate**: removes CO2 from the atmosphere.

### What affects the rate
- **Light intensity**: more light → faster up to a point.
- **CO2 concentration**: more CO2 → faster up to a point.
- **Temperature**: enzymes work best in a moderate range; too hot/cold slows them.
- **Water and chlorophyll levels**: shortages reduce photosynthesis.

### Quick analogy
Think of a chloroplast like a “solar-powered kitchen”: sunlight (power) runs machines (light reactions) that make ingredients (ATP, NADPH), which chefs (enzymes) then use to cook sugar (Calvin cycle) from CO2 and water.