Final answer:
Carbon dioxide and water are the two chemical substances needed to begin the photosynthesis process. The process releases oxygen and produces carbohydrate molecules.
Step-by-step explanation:
The two chemical substances needed to begin the photosynthesis process are carbon dioxide and water. These molecules, along with sunlight, are the necessary components for photosynthesis to occur. Once the process is complete, photosynthesis releases oxygen and produces carbohydrate molecules, like glucose, which contain the energy that living things need to survive.