Describe one common role of both bacteria and fungi in the movement of energy and matter in ecosystems. (b) describe how analyzing the data from the treatment group sprayed with water only will increase the validity of the experimental results.

The common role is decomposition.

Decomposition is a process by which organic substances, like leaves or dead animals, are broken down into simpler matter. 
A lot of different types of organisms, called the decomposers, will consume the organic substances and continue an essential part of the nutrient cycle. These organisms can be both bacteria and fungi.

This is important for recycling the organic matter that occupies space in the biosphere and that way, continue the movement of energy and matter in ecosystems.