Growth of Microbes

This activity will allow you to study the growth of microorganisms under conditions of light, dark, and filtered light as well as along an oxygen gradient.

Materials

four inch square of newspaper plastic wrap

hard boiled egg rubber band

bucket 250 mL of de-chlorinated water

1 tablespoon powdered chalk 2 L clear plastic bottle with top cut off

1 L of mud (best from the margins of ponds or marshes, or field soil)

sheet of red cellophane or tape (for one group only)

Procedure

1. Rip a newspaper into tiny bits

2. Crack a hard-boiled egg and break the yolk into bits. Discard the white and the shell.

3. Combine the mud and just enough water in the bucket to make a thick mud soup. Mix thoroughly. When the mud and water are combined, stir in the newspaper, egg yolk, and chalk.

4. Add the mixture to the bottle with a paper cup to one inch from the top. Tap the bottle lightly on the table to remove air bubbles.

5. Let stand for 30 minutes. Gently add enough water so that there is a top layer of water about a half inch deep above the mud surface.

6. Cover the bottle with plastic wrap and secure with a rubber band. The gas produced by the microorganisms is very smelly, so keep the plastic wrap on at all times.

7. Stand your bottle either in a well-lit area or in a dark place as instructed. Do not move the bottle.

8. Do not let the bottle dry out. Add or remove water to the top to maintain the half inch depth.

9. Observe and record changes with sketches and descriptions each day for six weeks. After the six week period is over, answer the questions below.

Questions

1. Did any changes occur in the bottle? If so, what is your evidence?

2. How many different life forms seem to exist?

3. Propose an explanation for the existence of the different things you see in the bottle.

4. Why might the layers be different?

5. Why might different microorganisms grow under different conditions?

6. What are the differences between the three columns?

7. How might these conditions be achieved in nature?