Here's why:

* Photosynthesis: Plants use carbon dioxide along with water and sunlight to produce their own food (sugars) through a process called photosynthesis.

* Respiration: Plants also respire, just like animals, where they break down sugars to release energy. This process uses oxygen and releases carbon dioxide. However, the amount of CO2 produced in respiration is much less than the amount used in photosynthesis.

So, while plants do use oxygen for respiration, their overall process of taking in more CO2 than they release makes them essential for absorbing carbon dioxide from the atmosphere.