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Rotting

This demonstration introduces students to the concept of biodegradation and the conditions that promote composting.

Biodegradation is the process by which organic substances are broken down by enzymes produced by living organisms. Biodegradation can be thought of as waste decaying or rotting. 

Biodegradable matter is generally plant and animal matter and other substances originating from living organisms. Biodegradable human-made products ranging from paper bags to egg cartons.

In normal environmental conditions, rotting is affected by:

  1. Availability of air: Many bacteria and fungi need oxygen from the air in order to live and begin the decomposition process.
  2. Temperature: Decomposers need a certain temperature to live. Many biological reactions will speed up in warm temperatures and slow down in cold temperatures.
  3. Availability of water: Decomposers need water to survive and reproduce.
  4. Chemical composition of food: the higher the nitrogen to carbon ratio the quicker organic matter will rot because decomposers can get more energy from nitrogen. It’s important to note that both carbon and nitrogen are important for growth, however.

​Landfills do not offer these conditions and therefore they cannot enable proper rotting. In fact, studies have found readable newspapers from the 1950’s in landfills, along with 25 year old grapes!

Average Time to Decompose:

Vegetables5 days - 1 month
Paper2 - 5 months
Cotton T-shirt6 months
Orange Peels6 months
Tree leaves1 year
Wool socks1 - 5 years
Leather shoes25 - 40 years

Objectives

  • Differentiate between compostable waste and non-biodegradable waste.

Materials

  • sealed bags of rotting fruit, vegetables or bread that decay at different rates (Allow rotting food 2–10 days to begin decomposing.)

  • paper

  • egg carton

  • regular plastics

  • 10-15 pictures of different types of garbage (organic and inorganic)

Key Questions

  • What foods take the longest to biodegrade? The shortest?
  • If organic waste is wrapped up in a plastic bag, will it degrade? Why or why not?
  • What are these products going to turn into once they break down?
  • If these products were in the landfill would they have the oxygen, water, and temperature they need to breakdown? What will happen to them?

What To Do

Set up

  1. Pass around the examples of rotting and not rotting products and discuss what affects the rate of rotting. Make sure any bags containing rotting materials are sealed tight.
  2. Hand out all the pictures of waste to students.

Challenge

  1. Put them in order of fastest to slowest to degrade. You can do this by:
  • lining up and holding a picture each.
  • laying out the pictures on a table.
  • attaching pictures to a board or wall using masking tape.
  1. Discuss if you have different opinions. Use the examples in bags to help out.

Teacher Tip: In addition to having students look at real rotting food and photos of rotting food, challenge them to match healthy and rotting food photos to see if they know what food can breakdown into as a follow-up activity

Extensions

  • Every day for 10 days, put a set of food items (one apple core, one piece of bread, one grape, etc.) into a plastic container and set the container on a shelf. Each day, compare the fresh food to the rotting food to see the changes taking place.