2. Photosynthesis: Storing Sunlight in Sugar

Photosynthesis is how plants, algae, and some bacteria capture light energy and store it as chemical energy in sugar. In plants it happens mainly in the chloroplasts, green organelles packed with the light-absorbing pigment chlorophyll.

The overall reaction is:
\[ 6\,CO_2 + 6\,H_2O + \text{light} \;\rightarrow\; C_6H_{12}O_6 + 6\,O_2. \]
In words: carbon dioxide + water + light → glucose (sugar) + oxygen. The glucose stores the captured energy; the oxygen is released into the air — the same oxygen most living things breathe.

Photosynthesis links life to the atmosphere: plants take in carbon dioxide and give off oxygen. It's also the base of most food chains, because it turns sunlight into the chemical energy that feeds nearly every other organism.

⚠️ Common misconception: a plant does not get most of its added mass from the soil. Much of a plant's new material comes from the carbon dioxide in the air, rearranged into sugars (the carbon comes from CO₂).

💡 Tip: photosynthesis = light in, sugar (and oxygen) out. It stores energy.