Read the book Rotten Pumpkin: A Rotten Tale in 15 Voices by David M. Schwartz. Lead a discussion about the role animals, insects, fungi, and bacteria play in the process of decomposition.
Tell the students that they are going to have the opportunity to observe the decomposition of a pumpkin. Show the students the aquarium or "decomposition tank." Explain to the students that the decomposition tank needs fresh soil from nature that contains decomposers (insects, fungus, and bacteria). Take them outside to collect soil from an area on or near the school, or obtain compost from a local nursery. Collect enough soil to fill 3-4 inches of the aquarium.
Ask the students how they will measure the observable changes that will occur in their pumpkin. Have the students record the characteristics of the pumpkin before it is placed in the decomposition tank. Students can draw a picture of the pumpkin and record the date, size, shape, and color of the pumpkin in their Pumpkin Science Journals.
Place the pumpkin into the soil so that it is partially buried. Moisten the contents of the aquarium with a spray bottle to simulate rain and cover the tank with several layers of plastic cling wrap. Tape the edges with packing tape.
Each week, the students will record observations in their journals. Instruct them to make note of any significant changes, such as mold growth or a pumpkin seed that begins to sprout. Have the students work in small groups to interpret the results of their observations and draw conclusions about the decomposition process.
Discuss interesting changes as they occur. When mold begins to appear on the pumpkin, ask the students, "What is the fuzzy stuff growing on the pumpkin?"
Show the video How Does Mold Grow? (stop at the 2:12 minute mark) to help students discover that mold is a fungus, mold spores live in the air, and mold spores feeds off of the food on which they land.
During the later stages of decomposition, ask the students, "Why does the pumpkin seem to disappear over time?"
Lead a class discussion about decomposition. Integrate the following points into the discussion:
The pumpkin doesn't actually disappear.
The pumpkin matter is eaten or broken down by other organisms.
Decomposers get the food they need by feeding on, breaking down, and absorbing parts of once living things.
As the investigation draws to a close, brainstorm ways the decomposition process could be sped up or slowed down. As an extension activity, have students design their own investigations, such as comparing the decomposition rate of different organic substances or observing how the decomposition process is affected by altering the variables of temperature, light, or water.
Cause and Effect: Events have causes, sometimes simple, sometimes multi-faceted. Deciphering causal relationships, and the mechanisms by which they are mediated, is a major activity of science and engineering.
Stability and Change: For both designed and natural systems, conditions that affect stability and factors that control rates of change are critical elements to consider and understand.
Activity 2: Pumpkin Planters
Provide each student with a mini pumpkin or place students in groups with one larger pumpkin per group. Tell the students that you are curious to know if a pumpkin can grow inside of a pumpkin. Conduct a class poll to determine how many students predict yes and how many predict no. Invite students from both sides to share why they answered yes or no.
Ask the students, "What is needed to grow a pumpkin?" (a pumpkin seed, light, the proper temperature, air, and water) "Where do pumpkin seeds come from?" (a pumpkin)
Have the students use garden trowels or spoons to fill their pumpkins with potting soil. Water the soil and place the pumpkins in a sunny spot. Ask the students if their pumpkin seeds have what is needed to sprout and grow into a pumpkin plant.
Each day, have the students observe their pumpkin plants and record observations in their Pumpkin Science Journals.
Activity 3: The Great Pumpkin
Read the book Life Cycle of a Pumpkin by Ron Fridell and Patricia Walsh or Pumpkins by Ken Robbins.
Use the students' experiences of sprouting a pumpkin seed and investigating a decomposing pumpkin (in Activities 1 and 2) to discuss the life cycle of a pumpkin plant. Include the following points in the discussion. First, the seed is planted. From the seed a plant sprouts, growing leaves and then flowers. From the flowers, small green pumpkins form. When the pumpkins are ripe, they turn orange and can be harvested. Inside of the ripe pumpkin are many seeds which can be planted to start the cycle again. Pumpkins left in the field will decompose leaving seeds that can sprout and grow into a new pumpkin plant the following year, continuing the pumpkin's life cycle.
Provide each student with the art items listed in the Activity 3 Materials List. Explain to the students that they will be creating a model of the pumpkin's life cycle.
Have each student draw a Jack-o-lantern face with a black marker or crayon on the back of one of the paper plates. Color the rest of the plate and the back of the second plate orange.
Trace the paper patterns onto the construction paper using the appropriate colors. Another option is to copy the pattern directly onto the construction paper. Cut the shapes out and punch a hole in the top of each one.
Thread the yarn through the holes of the seed, leaf, flower, green pumpkin, and orange pumpkin in the correct order of their formation on the pumpkin plant. Tie a simple knot at the top of each plant part.
Staple the end of the yarn closest to the orange pumpkin shape to the front of the plate without the face.
Staple the paper plates together around the edges with the orange sides facing out. Leave a gap on one side of the pumpkin to pull the seed, leaf, flower, and growing pumpkins out with the piece of yarn. Slide the string of plant parts into the center of the Jack-o-lantern.
The students can practice describing the life cycle of the pumpkin by slowly pulling the seed, leaf, flower, and growing pumpkins from the Jack-o-lantern.
Concept Elaboration and Evaluation
After conducting these activities, review and summarize the following key concepts:
Decomposition is a natural process through which nutrients are recycled back into the soil.
Plants need air, water, light, and nutrients to grow.
The life cycle of a pumpkin begins and ends with a seed.
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Discuss options for reusing leftover pumpkins. Make a pumpkin bird feeder.
Watch a giant pumpkin grow from a tiny seed in the video Giant Pumpkin Time Lapse or watch a time lapse video of pumpkins growing on a farm in the video, A Pumpkin's Life. Create your own time lapse video of pumpkin seeds sprouting or a pumpkin decomposing.
Create a compost pile on the school grounds. Add different types of organic substances to see which items decompose the fastest. Discuss how composting is a way to recycle food waste and limit the amount of garbage that is sent to the landfill. (Note: Do not use meat, dairy products, or any fatty material in the compost pile.) See Backyard Composting, Worms Eat My Garbage, or How to Compost for more guidance on starting your own compost pile.
Phenomenon chart adapted from work by Susan German. German, S. (2017, December). Creating conceptual storylines. Science Scope, 41(4), 26-28. German, S. (2018, January). The steps of a conceptual storyline. Science Scope, 41(5), 32-34.
Decomposing Pumpkin photo used with permission from Kevin Krejci.
Activity 3 adapted from an activity originally developed by Rose Judd-Murray.
Describe the characteristics of plants at different stages of their life cycles. For example: Use live organisms or pictures to observe the changes that occur during the life cycle of bean plants or marigolds.
Agricultural Literacy Outcomes
Plants and Animals for Food, Fiber & Energy
Explain how farmers work with the lifecycle of plants and animals (planting/breeding) to harvest a crop (T2.K-2.a)
Identify the importance of natural resources (e.g., sun, soil, water, minerals) in farming (T2.K-2.e)
Agriculture and the Environment
Describe how farmers use land to grow crops and support livestock (T1.K-2.a)
Describe the importance of soil and water in raising crops and livestock (T1.K-2.b)