Decomposition in freshwater
This lesson includes hands-on activities to demonstrate the process of decomposition in a freshwater ecosystem. It also focuses on the importance of decomposition and its critical role in the food chain.
A lesson plan for grade 6 Science
Students will be able to:
- Communicate the meaning and significance of decomposition.
- Work cooperatively to assemble leaf packs that will be utilized to illustrate decomposition in freshwater.
- Write descriptions and draw sketches of leaf packs before decomposition and after decomposition.
- Use lab equipment to weigh and prepare leaf packs.
Time required for lesson
- building blocks
- autumn-shed leaves (dogwood and maple work best; collect enough leaves for each group to have five grams)
- a scale that is able to measure five grams
- any type of fastener for the leaf packs (fishing line is good to sew with, plastic twist ties, etc.)
- foil pans
- any heat source (e.g. dryer, oven, etc.)
- zip storage bags (sandwich-sized)
- white paper
- colored pencils
- skewers (or any type of sturdy rod or stick)
Students should have a basic understanding of the food chain. It might also to be helpful to do a brainstorm activity to assess what students know about freshwater ecosystems prior to this investigation of decomposition.
If possible, have students bring in small bags of autumn-shed leaves, zip bags, and old foil pie plates or pans to class.
- Warm-up: Have students work in pairs for five minutes to define these two words. (Walk around the class to check for task understanding.)
- Class discussion: Ask students for their definitions. Encourage discussion towards portraying the two words as opposites. Examples:
- Composition—building, creating something new
- Decomposition—tearing down something that has already been built
- Hands-on activity:
- Pass out blocks to each group of students.
- Tell them they have five minutes to build a structure.
- Now ask the group to tear down their structures.
- Teacher: “Which part of your assignment was composition, and which part was decomposition?
- Check-up: distribute the real deal worksheet. Allow students to work in their groups to complete. Discuss answers with class.
- Concluding Activity: have each group create their own example of decomposition and composition. Have each group select a person to read it in front of the class. Have the class guess whether the example represents the process of composition or decomposition. Use the board or overhead to tally the examples.
- Lead in for next lesson: Focus on decomposition in nature, particularly in freshwater.
- Warm-up: Have students define the food chain, provide an example, and state why it is important. Share answers and write several examples on the board. Focus in on decomposition. Have students highlight the decomposition component of their food chain in their notebooks.
- Begin discussion of freshwater ecosystems. Develop a basic food chain for freshwater. Have students record in their notebooks.
- Discuss woodland streams and autumn-shed leaves that fall into the water. Pose this question to students: “What do you think happens to the leaves that fall into the water?” Discuss that living organisms decompose leaves. Have students understand that fallen leaves are a source of energy for stream life. At this point, you could have students visit the websites included in the plan to supplement the discussion.
- Have students work in groups to draw a woodland stream during autumn. Their pictures must include leaves falling into the stream and decomposition. It also must have labels and a title. Have students share their pictures with the class.
- Concluding Activity: Tell students that they will be investigating leaf decomposition in freshwater over a two week period.
- Students will work in groups to measure five grams of leaves.
- Students will need to soak their leaves in water in a foil pan or container for approximately ten minutes.
- Students will need to fasten the leaves together in a packet. (Choose the method which is most appropriate, safest, and cost effective for the teaching situation.) Make sure the left packets are snug.
- Students will need to tie their leaf packets to a stick or bar so they can place them in the stream and be able to locate them when it is time to retrieve the packets. Remember to label the sticks with each group name.
- Students will need to place their leaves in a bag with a group name label. Bags will need to be refrigerated until they are placed into the freshwater.
- Have students draw their leaf packs using colored pencils and have them write a few adjectives to describe the packs on their paper.
If you are fortunate, you will have a freshwater source on your campus or within walking distance. However, depending on your situation, you may have to travel to a stream or take the leaf packets to the stream without the students. Note: While a field trip to a stream is an excellent opportunity, it is important to stress safety around water. Have strict procedures for proximity to the stream and zero tolerance for horseplay to protect them and you!
- Place leaf packs with their sticks in the stream bed as sturdily as possible. Often rocks can be helpful. Shallow areas within streams are the best to use.
- If you are able to take the field trip, have the students draw basic stream diagrams focusing on living things that they see.
- Record the date that the packs were placed in the water. Leaf packs should stay in water for at least two weeks.
- After 2 weeks very gently place each leaf packet into a bag with its label.
- Have students place their leaf pack on a white sheet of paper. On another sheet of paper have students draw their leaf packets.
- Next have them compare this drawing to the drawing of their leaf pack before it was placed in the water. Ask them to formulate a reason why it has changed. Discuss. Focus on decomposition, point out leaves that look eaten or nibbled.
- Have students unfasten their packet and very carefully rinse off any sediment from each leaf. Place leaves loosely into a pan or container that can be placed in a heat source. Foil pans are the best.
- Place leaves in a drying source for several hours on low heat.
Last day of investigation
- Have students weigh their leaf packet and record the weight. If measurements were done correctly it should weigh less than five grams.
- Have them write and then discuss the changes they observed visually in their drawings as well as the changes they were able to measure using the scale. Collect these papers to use for assessment.
- Teacher observation and anecdotal notes during investigation noting participation
- Lab notebooks with diagrams
- All work can be collected and saved separately. Students can make it into a booklet including all activities listed above. It makes for a great mini-portfolio to display showing science concepts, cooperative learning, and hands-on activities.
This lesson was created during a summer internship in an ecology lab at UNC-Chapel Hill through the PREP program through MSEN. Special thanks to Dr.Seth Reice, Mrs. Diane Johnson, and to Mr.Wade Hoiland for their terrific assistance throughout this research experience.
North Carolina curriculum alignment
- Goal 1: The learner will design and conduct investigations to demonstrate an understanding of scientific inquiry.
- Objective 1.05: Analyze evidence to:
- Explain observations.
- Make inferences and predictions.
- Develop the relationship between evidence and explanation.
- Objective 1.05: Analyze evidence to:
- Goal 4: The learner will investigate the cycling of matter.
- Objective 4.02: Evaluate the significant role of decomposers.