How can you prove that a plant is breathing?

All organisms consume oxygen and release carbon dioxide. Plants still “feed”, that is, they absorb carbon dioxide and release oxygen (photosynthesis). This is very easy to test empirically. The easiest way to do this is to take the plant, place it in a glass jar, cover, and leave in a warm, dark place. After a while, gently lower the lit candle into the jar. The candle flame will go out as the plant has used up all the oxygen for breathing.