Plants primarily utilize carbon dioxide (CO₂) through the process of photosynthesis. During photosynthesis, plants take in CO₂ from the atmosphere and, using sunlight as energy, convert it into glucose (a type of sugar) and oxygen (O₂). The general equation for photosynthesis can be summarized as:
6 CO₂ + 6 H₂O + light energy → C₆H₁₂O₆ + 6 O₂
In contrast, cellular respiration is a process where plants (and other organisms) convert glucose back into energy, using oxygen and releasing CO₂ as a byproduct. However, it is not how plants utilize atmospheric CO₂ but rather how they process the products of photosynthesis.
So, the correct answer is: Plants process CO₂ through the process of photosynthesis.