Why was cow manure used as a potential source of starch degrading bacteria? 2. what are some other potential sources for starch degrading bacteria? 3. what component makes starch agar selective for starch degrading bacteria?

1.
Cow manure was used as a source of starch degrading bacteria because it contain amylase.
Amylase is an enzyme that breaks down complex carbohydrates molecules(starch)  into smaller molecules, making it possible to absorve those molecules.
Cows have this enzyme in their feces because they don't use it as much.
This will make the microorganisims in the manure use starch as their main food source.

2. Besides this use, Bacteria that degrade starch can be used in food, fermentation, textile and paper industries.
The genus Bacillus are an example of starch degrading bacteria.

3. Starch agar is selective for starch degrading bacteria because it tests the ability of an organism to produce amylase.
In this medium, there is Gram iodine that will react with the starch in the agar to create blue coloration plate.