Here's why:

* Photosynthesis is the process plants use to convert light energy into chemical energy. This chemical energy is stored in the form of glucose, a simple sugar.

* Glucose is a primary source of energy for plants and is used for growth, development, and other metabolic processes.

* Oxygen is also produced as a byproduct of photosynthesis, but it's not the primary end product.

While other molecules are produced during photosynthesis, glucose is the main product that serves as the foundation for the plant's energy needs and further metabolic pathways.