Here's why:

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

* Glucose is a simple sugar that serves as the primary energy source for plants and is also used to build other organic molecules.

* The initial products of photosynthesis are actually ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate). These are energy carriers that power the Calvin cycle, the stage of photosynthesis where glucose is ultimately formed.

Therefore, while ATP and NADPH are the first products, glucose is the first stable and readily usable product of photosynthesis.