The hay included as part of the culture medium provided a food source for bacteria. Bacteria are a good food source for some types of protists. a. Explain which group(s) of protists would not have survived because they have no way to produce their own food.
b. Explain which group(s) of protists would have survived without this food source.

Explanation:

The protist kingdom is composed of two main groups.  The principal difference between them is that algae can produce their own food, while protozoans need to ingest other organisms or organic molecules to survive.

Protozoans:

Microscopic unicellular organisms, eukaryotic and heterotrophs -predators or detritivores-. Most of them are aquatic free-living organisms, but some species are parasites. They feed on bacteria, other organic wastes, and other microscopic organisms. The phagocytosis process is normally used to ingest the food, invaginating their cell membrane.  

Algae:

Eukaryotic micro- or macroscopic organisms. Autotroph and photosynthetic. They might be either unicellular or pluricellular. They use sunlight to synthesize organic matter from water, CO₂, and mineral salts. Unicellular ones can be free-living or associate with others to form colonies. They are part of the phytoplankton and are ingested by heterotrophic organisms. Pluricellular algae do not create real tissues but they compose a tale. The depth at which they inhabit depends on the pigments they produce. All of them inhabit fresh or sea waters.