Here's the breakdown of the gases involved in photosynthesis:

* Goes into the leaf: Carbon dioxide (CO2) Plants take in carbon dioxide from the atmosphere through tiny openings called stomata on their leaves.

* Comes out of the leaf: Oxygen (O2) As a byproduct of photosynthesis, plants release oxygen back into the atmosphere.

Let me know if you'd like more details about the process of photosynthesis!