What substance, produced during photosynthesis,
provides food for plants and animals in a food
web?

Glucose is the substance produced during photosynthesis which provides food for plants and animals in a food web.

Explanation:

The main source of energy in a food chain or food web is made by the producers. These producers are mostly plants that make food by the process of photosynthesis. As a result of photosynthesis, glucose is made as the main product whereas oxygen is made as the by-product. Glucose made is used to drive energy for all the activities of the cell. This energy, released from glucose,  is carried within an ecosystem from one organism to another.