Here's why:

* Photosynthesis is the process where plants use sunlight, water, and carbon dioxide to create glucose (a sugar) and oxygen.

* Glucose is a complex molecule that contains chemical bonds. These bonds hold a significant amount of energy.

* The chemical energy stored in glucose is released when the plant (or an organism that eats the plant) breaks down the glucose through cellular respiration. This energy is then used for various life processes.

So, while plants initially capture light energy from the sun, they convert it into chemical energy in the form of glucose, which is the stored energy in food.