Oranges, like all citrus fruits, produce vitamin C (ascorbic acid) through a complex metabolic pathway called the L-gulono-gamma-lactone oxidase (GULO) pathway.

Here's a simplified breakdown of the process:

1. Glucose is the starting material, a simple sugar readily available in the plant.

2. A series of enzymatic reactions transform glucose into L-gulono-gamma-lactone.

3. The GULO enzyme catalyzes the final step, converting L-gulono-gamma-lactone into vitamin C (ascorbic acid).

Important Note: Humans and other primates lack the GULO enzyme, which is why we need to obtain vitamin C from our diet.