Food Decomposers

FIELD: Life Science DURATION: 30 min & daily checks for 1 week.
OBJECTIVE: Students will observe the decomposition of food by micro-organisms.
METHOD: Students directly observe the effects of yeast on food decomposition.
KEY VOCABULARY: Decomposition, yeast GROUP SIZE: Any


Decomposition is essential to the cycle of life on our planet. The three categories which all life on earth fit into are: producers, consumers, and decomposers. Decomposers consist of worms, fungi, and other microorganisms that feed on our leftovers.

Decomposers like fungi can be so small that we can't see them, only the results of their feeding. Yeast is a common form of fungus that's used in cooking to make bread rise as well as brew beer. Yeast is defined as a plant lacking chlorophyll, the photosynthetic chemical that generates energy from sunlight. Other fungi are mushrooms and mildew.

Dry yeast that is used in cooking is yeast that has gone into a sort of hybernation, or spore form. The yeast builds a strong outer coating to protect itself and doesn't need food for long periods of time (bacteria can also do this...for many years). Only when conditions outside this shell are favorable for survival does the yeast emerge and start eating and breathing again. In baking this is called activating and is accomplished by exposing the dry yeast to water. In this experiment you are activating the dry yeast by exposing them to the moisture of a banana.

In this experiment, you will place dry yeast on a banana slice and observe the effect this has on its decomposition over a week.

MATERIALS (per group):

2 slices of banana
2 plastic sandwich bags
dry yeast - 1/2 tsp. (2.5 ml)


1. Place a slice of banana inside each bag.
2. Sprinkle dry yeast on one slice. Mark this the "Y" bag.
3. Seal both bags and leave in a warm place.
4. Observe the bags daily for a week. Which banana slice shows the most and fastest decomposition? The yeast one should.


1. Try the experiment with different foods: apple, bread, other fruits. Which is decomposed faster by the yeast?

Created April 24, 1997 by Danica Nuccitelli.
Maintained by
Last updated April 24, 1997.