Prepare samples before beginning activity with students. First cover the sides and bottom of the beakers with the dark paper, so that the students cannot see inside. Place a label on each beaker and number them from 1 to 8.
Then place, each in its own beaker, the following samples numbered 1-4: soil, bread, rotten eggs, and one of the tap water samples. Cover the beakers with filter paper or cloth (so that the smell comes through but they cannot see the samples).
Repeat for samples 5-8: sulfur reducing bacteria, yeast, streptomyces coelicolor, and another tap water sample.
Prepare microscope slides or use premade slides of the yeast, the two bacteria samples and the tap water.