Natural Selection Image Map

Activity #3

Orientation
This activity is designed to allow students to observe the natural process of decomposition and understand the effects of different environmental conditions on the efficiency of decomposition.
Materials
Activity 3 Worksheet

Materials need to make a milk bottle compost system:

  • two 1 gallon plastic milk bottles
  • one smaller container, about 5-cm high, that fits inside the milk bottle
  • one Styrofoam plate or tray
  • drill or nail for making holes
  • duct tape or clear packaging tape
  • utility knife
  • two 2-liter or 3-liter soda bottles
  • one smaller container, about 5-cm high, that fits inside the soda bottle
  • one Styrofoam plate or tray
  • drill or nail for making holes
  • duct tape or clear packaging tape
  • utility knife
  • insulation materials such as sheets of fiberglass or foam rubber, or Styrofoam peanuts
  • fine-meshed screen or fabric large enough to cover top of soda bottle and air holes in bottom half
  • thermometer that will fit into the top of the soda bottle and be long enough to reach down into the center of the compost
  • chopped vegetable scraps such as lettuce leaves, carrot or potato peelings, and apple cores, or garden wastes such as weeds or grass clippings
  • bulking agent such as wood shavings or 1-2 cm pieces of paper egg cartons, cardboard, or wood
  • litmus paper
  • syringe or eye-dropper
  • optional: hollow tubing to provide ventilation

Compost Materials:

Bulking Agents

Food for the Microorganisms

wood shavings

lettuce scraps

small wood chips

carrot peelings

Newspaper strips

apple cores

pieces of paper egg cartons

bread crusts

Chopped straw

banana peels

 

weeds

 

grass clippings

Background

In the How We Know section of Exchange Cycles, you learned how it is possible to take advantage of the process of decomposition by making compost piles. Decomposition is the breakdown of organic (carbon-based) matter by microorganisms in the soil. Microorganisms get energy from organic matter and release carbon, nitrogen, and other nutrients to the soil in the process. This is the most efficient way to recycle organic matter. The microorganisms get their energy, the soil becomes more fertile, and nothing gets wasted. However, the conditions must be right in order for this process to occur quickly. Microorganisms need oxygen, water, and the right combination of carbon and nitrogen available to break down the organic matter efficiently. You can speed up nature's method of decomposition by a process called "composting."

In this activity, you will work within groups to conduct two different composting experiments. In the first experiment, you will evaluate the efficiency of different composting conditions. In the second experiment, you will evaluate the efficiency of decomposition of different substances that have different capacity for decomposing. Decomposition releases large amounts of energy. Therefore, you can continuously measure the amount of decomposition in each system by measuring the heat produced in each system. The procedure for building the compost system used in this experiment are adapted from the Cornell Composting Web Site. http://www.cfe.cornell.edu/compost/soda.html

 

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