Here's why:

* Cellular respiration is the process by which organisms break down glucose to release energy in the form of ATP.

* Plants are autotrophs, meaning they produce their own food through photosynthesis. This process uses sunlight to convert carbon dioxide and water into glucose, storing energy within the glucose molecules.

So, while plants do use cellular respiration to release energy from the glucose they make, they don't use it as a primary energy source. They primarily use photosynthesis to generate energy.