The Calvin-Benson cycle, also known as the light-independent reactions of photosynthesis, utilizes three key substances to produce sugar molecules:

1. Carbon dioxide (CO2): This is the main source of carbon atoms that are incorporated into the sugar molecules.

2. ATP (adenosine triphosphate): This molecule provides the energy needed to power the reactions within the cycle.

3. NADPH (nicotinamide adenine dinucleotide phosphate): This molecule acts as a reducing agent, providing electrons to convert carbon dioxide into sugar.

These three substances work together to create a complex series of reactions that ultimately generate glucose (a sugar molecule) and other organic compounds.