Student Activity - Biodegradability experiment

Activity idea

In this activity, students set up an experiment to determine the biodegradability of different substances.

This experiment can be done in groups, with each group given the same or different items from the list below, or each group could be assigned two materials to compare, for example, plastic versus cardboard.

Your students could also develop a hypothesis about what material will be more biodegradable or what might happen if they were to put items in different locations.

Instructions

What you will need:

A spade or trowel

A 10 cm x 10 cm piece of each of the following:

• Plastic foam (from a plate or a meat tray)
• ‘Biodegradable’ plastic shopping bag
• Plastic shopping bag
• Cardboard
• Thin woven cotton fabric
• Piece of lettuce/cabbage leaf
• Aluminium foil

A coloured marker

A sheet of acetate with a fine grid (5 mm squares) copied onto it.

Instructions:

• Locate an area where the samples will be buried.
• Dig a 30 x 30 cm square hole that is at least 10 cm deep. (It will make it easier to dig a hole if the study area is watered a day or two before the experiment is to begin.)
• Place the samples in the hole so that they are not resting on top of each other.
• Cover the samples with soil.
• Place a marker over the samples so that you can find them when it is time to dig up the samples.
• Wash your hands.
• After 14 days, return to the site and carefully dig up the samples.
• Carefully place the samples on a tray or in a box lid to carry them inside. Note: The samples may be brittle and may tend to fall apart.
• Place the 10 x 10 cm clear plastic acetate grid over each sample.
• Mark on the grid any area that shows that the material is changing or breaking down.
• Count the squares marked and record the number for each material in a chart.

Analysis

Create a graph of the data or collate the data as a class and then graph the data.

Group the materials into categories (not based on their biodegradability).

• How did you decide on those categories?
• What was the most biodegradable category?
• What was the least biodegradable category?

Group your most biodegradable items and your least biodegradable items together.

• Can you see anything that links these items?

Based on this, can you predict how biodegradable the following items might be?

• a sheet of paper
• a sheet of plywood
• a cotton sock
• a synthetic sock
• a paper plate (waxed)
• a fizzy drink can
• a plastic bottle

Questions

• Did your results match those of other groups?
• If your results were different, what do you think might have been the reason?
• Did the outside temperature have any impact on biodegradability?
• What were your conclusions for this experiment?
• What could you infer based on your conclusions?
• How would you design this experiment differently the next time?
• How do we know what variables and what changes to variables in an experiment led to the results?
• What is the purpose of a control? Does time make a difference to the results?