Students know how plants use carbon dioxide (CO₂) and energy from sunlight to build molecules of sugar and release oxygen.

Two features of photosynthesis make it the most important chemical reaction from the point of view of Earth’s creatures. First, it captures the energy from sunlight and packages in it chemical form (sugars). Second, it takes carbon dioxide gas and makes a much more complicated carbon-containing molecule from it (sugar, again).

Organisms do two opposite things with the sugar made through photosynthesis. They break it back down to carbon dioxide to get the energy that was stored in it. They also build it up into much larger molecules that become the very fabric of their bodies. Almost all of Earth’s ecosystems depend on photosynthesis for both energy and chemical structure.