Plants are the bottom trophic level of the food chain. The organisms at this level are the primary producers, or autotrophs that make their own food. Plants use the energy of the sunlight they receive to make glucose via photosynthesis. The heterotrophs (animals) then eat the plants and the energy moves up the food chain accordingly.
The entire movement of energy up the food chain is quite inefficient. Fortunately, the Sun gives off a nearly inexhaustible, constant source of energy to start the whole flow of energy. Plants only convert about 1% of the energy they receive from the Sun into chemical energy, or food, via photosynthesis. Plants do consume some energy. They do metabolize some of the glucose made to produce energy for growth. Growth is the primary way that plants use energy. And of course all of these chemical reactions produce heat which is another form of energy. But they ultimately produce more food than they consume. As the energy moves up the food chain, only about 10% of the food energy is used to produce new biomass. The remaining 90% is lost to energy consumption and heat. I cannot find any specific energy numbers for these transformations, but you can see that the entire process is not very energy efficient.