Bacteria and fungi are found in all ecosystems on Earth. A scientist claims that fungi are keystone species in a particular terrestrial ecosystem. To test this hypothesis, the scientist divides an area within the ecosystem into multiple small plots of similar size. Equal numbers of plots are then randomly assigned to one of three treatment groups. Plots in the first group are sprayed with a water-soluble substance that selectively kills fungi. Plots in the second group are sprayed with a water-soluble substance that selectively kills bacteria. Plots in the third group are sprayed with the same volume of water only. After a certain period of time, the scientist then measures the amount of accessible nutrients in the soil in each plot.
(a) 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.