Photosynthesis is a process in which energy is converted to energy.

Photosynthesis is a process in which light energy is converted to chemical energy.

Organisms, such as plants, that carry out photosynthesis absorb light from the Sun and, through a series of chemical reactions, produce sugar (glucose) molecules. These sugar molecules may be stored by the photosynthetic organism, or the chemical bonds in the sugar can be broken down by the organism to release energy for its life processes.

i believe it is "they are not used up by reactions" as the answer to your question, text me back if this is correct because i just learned this.