Grade Level/Subject
9-12 / Bio 2 (Environmental Science)
Unit
Sustainability
Enduring
Understanding
Today’s decisions define our future
environment.
SOL Objectives
BIO.8 The student will investigate and
understand dynamic equilibrium within
populations, communities, and ecosystems.
Key concepts include
d) the effects of natural events and human
activities on ecosystems
ES.1 The student will plan and conduct
investigations in which
a) volume, area, mass, elapsed time,
direction, temperature,
pressure, distance, density, and changes in
elevation/depth are
calculated utilizing the most appropriate
tools;
b) technologies, including computers,
probeware, and geospatial
technologies, are used to collect, analyze,
and report data and
to demonstrate concepts and simulate
experimental conditions;
c) scales, diagrams, charts, graphs, tables,
imagery, models, and
profiles are constructed and interpreted;
d) maps and globes are read and interpreted,
including location
by latitude and longitude;
e) variables are manipulated with repeated
trials; and
f) current applications are used to reinforce
Earth science
concepts.
ES.11 The students will investigate and
understand the origin and evolution of the
atmosphere and the interrelationship of
geologic processes, biologic processes, and
human activities on its composition and
dynamics. Key concepts include
d) potential changes to the atmosphere and
climate due to human, biologic, and geologic
activity.
Title
Observing Decomposition Lab
Lesson Objective
To study how various factors affect
decomposition.
Inquiry Level
3/4
Materials Required
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2 L clear plastic pop bottle
Hand trowel (to gather soil)
small nail and/or push pin
grass clippings, leaves, twigs and soil,
scissors
shredded paper/newspaper
150 mL beaker
food scraps (banana peels, pieces of
apple, bits of bread, etc. NO meat or
bones, please!)
 Sharpie marker
 Cheesecloth
 tray to keep bottle on
 rubber bands,
 plastic fork or twig to stir with
 water
 seeds
 rulers
 thermometers
Possible things students may request
 soil pH testers
 worms
 probe ware to test soil.
 Heat Lamp
 Refrigerator
 Freezer
 Etc (other things students may
request)
Note – This is a very open-ended lab. Students actually come up with their own
question to test, but you may guide them in this process, or assign them a
question all-together.
Name: ______________________ Period: _______ Date: ________________Score _______ / 20pts
Observing Decomposition Lab
Background
Soil is the loose material on the Earth’s surface in which plants can grow. The top layer of soil (topsoil) is
dark in color in some areas because it contains humus. Humus is formed when decomposers break down
organic material (the remains of living organisms such as plants and animals), releasing nutrients such as
carbon, nitrogen, and phosphorus that can then be used again by plants for growth. This form of natural
recycling is a slow, continual process. It takes nature 250 to 2,000 years to produce one inch of topsoil!
Decomposition is the process in nature that returns nutrients to the soil through the cycling of matter.
The amount of moisture, light, heat, the source of bacteria and fungi, and the nature of the decomposing
material are all important variables in the process. In addition, decomposition requires oxygen.
There are several different types of decomposers: fungi (mushrooms and bread molds) cannot make their
own food as plants do, so they must absorb their nutrients from either dead or living organisms. Bacteria
are microscopic, single-celled organisms that also absorb their nutrients from other organisms. The tiny
sow bug, like some insects and other animals, digest organic matter and deposit the decomposed material
as a waste product. Earthworms also contribute to the soil in this manner, and their movement through
the ground helps to aerate the soil. Cows similarly contribute to the recycling process. Their digestive
tracts contain decomposers (bacteria) that turn grasses and grains into a nutrient-rich waste product,
called manure.
In this investigation, you will explore the process of decomposition and making compost. More and more
people compost their garbage at home, many times in a compost pile in the backyard or garden. The goal
is for food scraps in the compost pile to decompose over time. If done properly, it is safe, free of
unpleasant odors, and beneficial to plant growth! Thanks to the action of bacteria, fungi, and worms, the
garbage breaks down to form a dark-colored, nutrient-rich substance called compost.
The best compost “recipe” includes a combination of carbon-rich brown materials (dry leaves, plant
stalks, pine needles, small twigs, wood shavings, shredded newspaper) and nitrogen-rich green materials
(fresh leaves, lawn clippings, fruit and vegetable scraps, coffee grounds, tea bags). Carbon is the spark
that starts the composting process. Nitrogen fuels the microorganisms that decompose materials. General
rule of thumb says to add 3 times as many brown materials as green materials. Do NOT compost meat,
bones, animal waste, dairy products, or any inorganic material.
Advance Preparation
Pre-Lab Research – Use your book or the internet.
1. What are some variables that could affect the decomposition process?
2. What are the best conditions to make compost?
Experimental Design – Each group will have at least two compost bottles to work with and at least 1
month to conduct the experiment. Use your research in the previous section to select your variables and
design your experiment. Read through the materials below and over the basic procedures to choose what
variable you want to test (independent variable), how you will measure the process of decomposition
(dependent variable), what conditions you will keep constant in your experiment, and your number of
trials. After that, write a formal title, research question, and hypothesis. Fill in the chart below with all of
this information. Once you have filled out the table below, meet with your teacher to discuss your plan.
Question: What is the effect of _________________________on the process of decomposition?
Hypothesis: _________________________________________________________________________
____________________________________________________________________________________
Independent Variable (What you change on purpose to test): _________________________________
Dependent Variables (What you measure): ___________________________________
Control Group: ________________________________
Constants (at least 4): _________________________________________________________________
____________________________________________________________________________________
Number of Trials: __________________
Available Materials (per team)
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
2 L clear plastic pop bottle
small nail and/or push pin
scissors
150 mL beaker
Sharpie marker
cheesecloth
rubber bands








Hand trowel (to gather soil)
grass clippings, leaves, twigs and soil
shredded paper/newspaper
food scraps (banana peels, pieces of apple, bits of
bread, etc. NO meat or bones, please!)
tray to keep bottle on
plastic fork or twig to stir with
worms
water
What other materials will you need for your experiment?
SUGGESTED PROCEDURES – These are the most basic procedures that you should use to construct your
decomposition chambers. Each group will be doing a variation of these procedures according to their
experimental plan. Please change, add, or delete any procedures that you do that are not listed below so
that these procedures reflect your experiment.
PART A: Prepare the Decomposition Bottle
1. To prepare the bottle, carefully poke holes in the sides and bottom of the bottle. Use the push pin
for smaller holes on the sides and the nail for larger holes on the bottom (after starting small holes
with the push pin). Use Figure 1 as a guide.
2. Using the nail, poke a large hole near the top of the bottle at the point where the sides become
vertical and the plastic thins out. Starting at this hole, carefully cut off the top of the bottle with
the scissors as shown in Figure 2. Be careful as the cut plastic can be sharp!
3. Use a Sharpie marker to label your bottle near the top with the names of the people in your group
and the date. Then get a 150 mL beaker and a hand trowel for your group to take outside.
PART B: Gather Materials Outside
4. When the class is ready, head outside to gather the required grass clippings, leaves, twigs and soil.
All materials should be torn into small pieces. Fill the bottle one-third full with…
 grass clippings (pull grass with your hands)
 leaves (use leaves from a variety of plants)
 small twigs or dried material, and
 ~150 mL loose soil (dig up a small area using the trowel; minimal damage, please!)
PART C: Complete Decomposition Bottle
5. After returning to the classroom, cut the food scraps into pieces no larger than 1 cm across before
adding them to the bottle. A team member should also add some shredded paper to the bottle,
also cut into pieces no larger than 1 cm across.
6. When all the materials have been added, put the bottle on a tray BEFORE adding a
small amount of water. The contents of the bottle should be moist, but NOT
soaking wet.
7. Use a plastic fork to mix the contents of the bottle well. If the contents are still dry, add a little
more water. It is important to thoroughly mix the contents, so all the materials can interact!
8. Use a Sharpie to clearly mark the initial height of the contents, and note today’s date. Cover the
bottle with a piece of cheesecloth and secure the cheesecloth with a rubber band.
9. Follow the clean-up instructions below, before recording your first set of data about the contents
of the bottle.
 Wash & dry all equipment used and return it to where you found it.
 Clean your lab table using the sponge and lab soap provided.
 Wash your hands well, with soap and water.
10. Once your lab station is clean, then record observations in your lab notebook about your
decomposition bottle as suggested below.
Data / Observations
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You will make frequent observations of your decomposition bottle. Keep a record of each
observation in your lab notebook, being sure to include the following:
 Date of observation
 Description of any changes that occur:
- quantitative data (height of the contents)
- qualitative data (change in color, odor, or organisms present)
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After you have made your observations, add some water if the contents are dry and mix well with
a fork. Mark the new height on the side of the bottle and record the date. Make sure you replace
the cheesecloth when you have finished making your observations.
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FOR FUN: Only on the last observation day – Add seeds! Which bottles will have the best
compost?
Lab Analysis (to be completed at end of experiment)
Graph – Graph all of your data on a separate sheet of paper and attach to your lab.
Conclusion Paragraph- This should be written in paragraph form. Make sure you address all questions and write in
complete sentences.
1. What was the purpose of the experiment?
2. What were the major findings and was your hypothesis supported by your data?
4. What recommendations do you have for improving or expanding this experiment?
5. How is this experiment relevant or helpful to society?
Summative Questions
1. How did the contents of the bottles change over time? What has happened to the food items that
you originally placed in the 2-liter bottles? Specifically describe the changes that were observed
over the past weeks. (Use the notes you recorded in your lab notebook!)
2. How did your different bottles differ from each other? Why do you think this happened?
3. Decomposers break down the food scraps over time in this experiment. Which decomposers are
visible to the naked eye? Which decomposers are not? Did you observe any of these decomposers
during your experiment?
4. What did you do in the lab to introduce decomposers to your decomposition bottle? Where must
they have come from?
5. As a result of the decomposition process, what remains of the original food scraps you added to
the bottles? (Hint: the answer isn’t “nothing!”)
6. Why was it important to continue to stir up the contents of the bottle over time?
7. There is evidence of four nutrient (matter) cycles within your decomposition bottle. For each,
identify the nutrient/matter that is recycled, and how this happened in your bottle. (Hint: use the
Background Information to help you!)
8. What would be the benefits of creating and maintaining a compost pile in your backyard? Name
as many as you can think of!