Lesson Plan: What is Biodegradable?
Science, level: Elementary
Concepts Taught: Some materials decompose when buried; others do not. Microorganisms play a vital role in the decomposition process.
Objective:
Students will be able to differentiate between the kinds of material that
nature recycles in soil and those it does not. Students will make predictions
about materials which will decompose and their rates. Variables which will be
held constant will be examined and defined.
Materials:
1. ten pieces of each of the following:
- glass
- paper
- steel or other metal
- plastic
- apple, lettuce, or other fruit or vegetable
2. ten containers, jars, or flower pots
3. soil
4. sterile potting mix
5. masking tape or labels
6. handout: WATCHING WASTES ROT: RECORD
Keywords:
biodegradation, decomposition, microorganisms
Background:
Decomposition occurs everywhere. If everything existed forever, we would
be buried in our waste. Our waste products are varied: some are made of easily
degradable materials while others will last for thousands of years.
Procedure:
1. Display a piece of glass, paper, metal, plastic, and food. Ask the
class to predict which of these substances are biodegradable (capable of rotting
or decomposing)? Conduct the following experiment to determine whether their
predictions were correct.
2. Dig enough soil from a garden or vacant lot to fill five containers.
(One pound cottage cheese containers would be suitable.) Fill five of the
containers half full with soil, and the other five half full with sterile
potting mix. Place a piece of each type of waste into each container. Continue
filling the containers with soil or sterile mix, whichever they already contain.
Add enough water to all pots so that the soil or sterile mix is damp but not wet
to the touch. Cover the containers. Label the containers to indicate the type of
waste and whether it contains soil or sterile mix.
3. After one week, examine the waste in each container. Which wastes are
decomposing? Cover the wastes again, and continue to check them once a week for
as long as you want. Record your observations.
4. Check the original predictions and draw conclusions about which
substances are biodegradable and under what conditions.
Follow-Up:
1. Explore degradable plastics. Many producers of plastic bags are now
producing plastic bags they say will degrade. There are two types of degradable
plastic bags; photodegradable and corn starch biodegradable.
2. Find out what makes these plastic bags degrade and perform an
experiment similar to the one above.
Questions to be considered:
- What makes these plastic bags degradable?
- Does the whole bag degrade? Are there any waste products left over?
- Which items decomposed most quickly?
- Which items didn't decompose at all?
- In general, did items decompose more quickly in compost or in sterile mix? Why do you think this is true?
Watching Wastes Rot: Record Form (PDF)
