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Anytime Lesson Plan: Composting: A Scientific Investigation


By conducting this scientific investigation involving decomposition, students will learn that the life cycle of trash is affected by its organic or inorganic nature.



In this lesson, students will:

  1. learn that trash is composed of two types of waste: organic and inorganic.
  2. learn that organic waste is composed of plant and animal material and has a full-loop life cycle.
  3. learn that inorganic waste is composed of material other than plant and animal matter, such as sand, dust, glass, metal, and plastic and has a linear life cycle.
  4. learn that decomposers such as fungi, microorganisms, and insects are important in the decomposition of organic waste. 
  5. learn that composting is one way that we enable organic trash complete its full-loop life cycle.
  6. learn how to conduct a scientific investigation.


  • mason jars (6)
  • pieces of trash: an apple core, a piece of plastic, two leaves from outside, a piece of bread, a
  • piece of tin or aluminum foil, and a piece of paper
  • soil, enough to fill six jars (from outside, not store-bought) 
  • composting workbook (1 per student)


  • organic waste: waste from organisms or the products of their life processes
  • inorganic waste: waste not from organisms or the products of their life processes
  • decompose: to separate or resolve into components or elements; disintegrate
  • decomposer: an organism, usually a bacterium or fungus, that breaks down the cells of dead plants and animals into simpler substances
  • full-loop life cycle: a life cycle for a material that never comes to an end.  Examples are organic waste like food scraps or lawn trimmings that are composted and turned back into the soil from which they came.
  • linear life cycle: a life cycle for a material that comes to an end.  For example, plastic is made from fossil fuels mined from the Earth, but its life cycle will end in a landfill. 
  • compost: a mixture of decayed or decaying organic matter used to fertilize soil
  • microorganism: an organism that can be seen only with the aid of a microscope and that typically consists of only a single cell. Microorganisms include bacteria, protozoans, and certain algae and fungi.



  1. Collect all necessary materials
  2. Print enough double-sided copies of the composting workbook for each student to have one.


Explain the difference between organic and inorganic waste.  Show students examples of things we may throw in the trash, and have them decide whether they are organic or inorganic by determining what they are made of.

Hold up each piece of trash that will be part of the experiment (an apple core, a piece of plastic, two leaves from outside, a piece of bread, a piece of tin or aluminum foil, and a piece of paper) and ask the students to determine whether the item is organic or inorganic.  (The apple core, paper, leaves, and bread are organic; plastic and tin are inorganic.)

Next ask the students what causes waste in nature, like dead plants and animals, to disappear.  Explain that decomposers are things that eat dead matter and release nutrients back into the soil. 

Ask the students to name some decomposers.  Make sure they list bacteria, fungi, insects, and other microorganisms.  Make sure they understand that these are tiny creatures that live in the soil, who turn waste back into soil.  Also explain that decomposers feed solely on organic waste, and that they do not break down inorganic waste like plastic and metal. 

Next, introduce the scientific method. Explain that scientists conduct experiments to understand how things work, and that the students will be conducting a scientific investigation on composting. Explain that this involves asking a question, formulating a hypothesis, conducting an experiment, rejecting or accepting the hypothesis (analysis), and discussing the results.  This procedure is outlined for the students in the workbook.



  1. In the workbook, have each student write out a question that they are trying to answer with this experiment (guide them to ask questions such as “Which kinds of trash will take the longest to break down?”)
  2. Have students hypothesize whether or not each piece of trash will decompose by the end of the seven week experiment.  Make sure they consider whether the object is organic or inorganic.
  3. Have each student record initial observations of each object.  Make sure they include size (length, width, and height), color, shape, and a simple sketch.
    Initial Observations
  4. In front of the class, where everyone can see, place each trash item in a clean, empty mason jar.  Try to place the item against the glass, so you can monitor it over time.
  5. Fill each mason jar to within 1 inch from the top with soil.  Make sure the soil is from outside to ensure that it contains the bacteria and microorganisms necessary for decomposition.  The soil should naturally contain decomposing bacteria, fungi, and microorganisms.  Don’t worry if you see small insects, the more the better. Soil not including these decomposers will cause the trash to take much longer to break down.
    Add soil
  6. Add a few tablespoons of water to the jar, and keep the lid off.  Continue adding water to each jar as necessary to keep the soil moist but not soaked over the next seven weeks.
  7. Each week have the students record observations for each trash item in their workbooks.  They should note color, shape, and size of all the objects, and even include a sketch if they want. (This will get more difficult as things turn to soil.)
  8. At the end of seven weeks record final observations in the last box. They should observe a tremendous difference in some jars between the first and last week – as evidenced below.
    Initial Observations 
  9. In the workbook, under the “analyze your data” section, have the students decide whether they can accept or reject their hypothesis and write why.
  10. Finally, under the “conclusion” section, have students summarize what happened over time to each piece of trash, and encourage them to draw conclusions about different types of trash and how decomposition works.  Ask the students which pieces of trash decomposed the most?  Why?  Which didn’t decompose at all? Why?


After the experiment is over, discuss the differences between organic and inorganic trash decomposition, in terms of time.  Prompt the students to discuss the differences between full-loop and linear life cycles.  Ask which is better for the environment, and why is it important that we let waste complete its life cycle.

Assign as homework or discuss the following questions: 

  • What are the benefits of composting for the environment?  (It returns essential nutrients back into the soil.  If organic waste is landfilled, it permanently removes those nutrients from the earth.)
  • Name some decomposers and explain why they are important.  (Bacteria, fungi, beetles, ants, flies.  All of these organisms eat decaying animal and plant matter, returning nutrients back into the earth.  It may appear that matter breaks down by itself, but in reality we just cannot see all of these organisms hard at work.  Without them dead matter would never convert back into nutrients and Earth’s ecosystems would not function properly.)
  • What are the differences between organic and inorganic waste?  Which one takes longer to break down?  Why?  (Organic waste is made of matter that was once alive, like plants and animals.  Inorganic matter is made of matter that was not alive, like rocks and minerals.  Inorganic matter takes longer to break down, because it is not decomposed by other organisms.  It is left to break down on its own with the help of the sun and water, which takes a very long time, sometimes thousands of years.) 
  • Does organic trash have a full-loop or linear life cycle? Why?  (If organic trash is allowed to compost and decompose, it will have a full-loop life cycle because its nutrients cycle from the earth, to an organism, to a product we use, and then back into the earth.) 
  • Does inorganic trash have a full-loop or linear life cycle? Why?  (Inorganic trash has a linear life-cycle because the matter is taken from the earth, formed into a product, used and than cannot be returned back to its natural state.  An example is a plastic bottle.  It cannot be broken down back into naturally occurring fossil fuels.) 
  • What can we do at home to help organic trash complete its life cycle?  (Compost!)
  • What can we do at home to keep inorganic trash from piling up in landfills?  (Use less products made of non-recyclable materials, and recycle everything we can.)



As a way to integrate English Language Arts, read Shel Silverstein’s Sarah Cynthia Sylva Stout. Print out copies of the lyrics or write them out together on the board. Have students underline all the nouns in the poem. Then, decide as a class which of the nouns are compostable!



California Content Standards

Grade Two

Investigation and Experimentation

  • 4a. Make predictions based on observed patterns and not random guessing.                              
  • 4d. Write or draw descriptions of a sequence of steps, events, and observations.           

Grade Three

Investigation and Experimentation

  • 5b. Differentiate evidence from opinion and know that scientists do not rely on claims or conclusions unless they are backed by observations that can be confirmed.
  • 5d. Predict the outcome of a simple investigation and compare the result with the prediction.
  • 5e. Collect data in an investigation and analyze those data to develop a logical conclusion. 

Grade Four

Life Sciences

  • 2c. Students know decomposers, including many fungi, insects and micro-organisms, recycle matter from dead plants and animals.

Investigation and Experimentation

  • 6a. Differentiate observation from inference (interpretation) and know scientists’ explanations come partly from what they observe and partly from how they interpret their observations. 
  • 6b. Measure and estimate the weight, length, or volume of objects.
  • 6c. Formulate and justify predictions based on cause-and-effect relationships.
  • 6f. Follow a set of written instructions for a scientific investigation. 

Grade Five

Investigation and Experimentation

  • 6b.  Develop a testable question.
  • 6g. Record data by using appropriate graphic representations (including charts, graphs, and labeled diagrams) and make inferences based on those data. 
  • 6h. Draw conclusions from scientific evidence and indicate whether further information   is needed to support a specific conclusion.
  • 6i. Write a report of an investigation that includes conducting tests, collecting data or examining evidence, and drawing conclusions. 

Grade Six

 Investigation and Experimentation

  • 7a. Develop a hypothesis.
  • 7d. Communicate the steps and results from an investigation in written reports and oral presentations.
  • 7e. Recognize whether evidence is consistent with a proposed explanation.

Grade Seven

Investigation and Experimentation

  • 7c. Communicate the logical connection among hypotheses, science concepts, tests conducted, data collected, and conclusions drawn from the scientific evidence.

Grade Eight

Investigation and Experimentation

  • 9a.  Plan and conduct a scientific investigation to test a hypothesis.



The average American generates 4.6 pounds of trash a day which adds up to 1,642.5 pounds a year (EPA 2006).  San Francisco has one of the most successful recycling and composting programs in the country, reporting that as much as 69% of trash is diverted away from landfills to recycling and composting facilities (Mayor’s Office of Communications 2007).  Although this is a highly successful program, lots of trash still needlessly ends up in a landfill. More thorough recycling and composting could keep almost all our residential waste from the landfills.

There are two main types of trash that humans generate: organic and inorganic.  Organic waste consists of plant and animal material, such as uneaten food and lawn scraps.  This is the same type of waste that is generated in natural ecosystems, when plants and animals die.  In nature, the plants and animals decompose, or break down into their principal nutrients with the help of insects, bacteria, and other microorganisms.  These creatures are called decomposers and they play an extremely important role in nature; without them the Earth would be piled high with dead things.  Once decomposition occurs, the nutrients are absorbed back into the soil where they play an important part in soil health.  This nutrient-rich soil is then available to nourish new plants, which in turn nourish animals. Thus the “waste” is completely recycled into new life.  This is considered a full-loop life cycle because the materials are constantly recycling themselves through the ecosystem.  When humans throw their organic waste into the trash, it ends up in a landfill where it is unable to complete its life cycle.  It will eventually break down, but it will not return its nutrients to the soil. One way that we enable organic waste to complete its full-loop life cycle is through composting.  When we throw our organic waste into a composting pile, it decomposes and turns back into nutritious soil that can in turn be used to nourish plants. This is a great way to add healthy nutrients to the soil and conserve valuable landfill space at the same time.

Inorganic waste is trash composed of items not derived from plant and animal sources and cannot be broken down by decomposers. Examples of inorganic waste are plastics and metals.  This type of waste does not decompose quickly. Plastic and metal will spend thousands of years in a landfill, and although they may breakdown into smaller pieces over time, with the help of sun and water, they will not provide nourishment for new life to grow.  This is called a linear life-cycle, because the life of the material ends when it is thrown away.
composting diagram


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