Here's why:

* Photosynthesis is the process by which plants, algae, and some bacteria use sunlight energy to convert carbon dioxide and water into glucose (a sugar) and oxygen.

* Carbon dioxide is absorbed from the atmosphere through tiny openings on the leaves called stomata.

* Water is absorbed from the roots and transported to the leaves.

The chemical equation for photosynthesis summarizes this:

6CO2 (carbon dioxide) + 6H2O (water) + light energy → C6H12O6 (glucose) + 6O2 (oxygen)