A scientist fills a glass container with water and places in aquatic plant inside the container then closes the lid and places the container in direct sunlight the scientists observe small bubbles on the surface of the plant's leaves on days one and two but no bubbles on day three the scientists concludes that the bubbles were caused by photosynthesis which substance should be added to the water in order for the bubbles to reappear?

The substance that should be added to the water in order for the bubbles to reappear is carbon dioxide (CO2).