Energy Flow: Where Does it Go?
- Identify the source of energy.
- Construct a food chain of at least four members.
- Define producers, consumers and decomposers.
- State at least three ways plants and animals use energy.
- Construct a food pyramid.
- Construct a food web from a list of organisms.
Pa. Standards Addressed Doing the Activity
- Teaching Methods Assessment and Evaluation
- Background Extensions
- Getting Ready References
Pa. Environment & Ecology Standards Addressed:
- 4.6.7. Ecosystems and their Interactions
A. Explain the flows of energy and matter from organism to organism within an ecosystem.
B. Explain the concepts of cycles.
C. Explain how ecosystems change over time.
- 4.7.7. Threatened, Endangered and Extinct Species
A. Describe diversity of plants and animals in ecosystems.
Other PA Standards Addressed
- Science & Technology
- Reading, Writing, Speaking and Listening
Teaching Methods Incorporated
Whole-body, Hands-on, Observation, Calculations, Data Collection, Game, Small Group, Discussion, Investigation, Analyzing
- Food web cards
- Choose one: 1 large box full of packing peanuts, popcorn, leaves, etc.
- “Food Web” Worksheet for each student
- Lap boards
In every ecosystem, energy flow goes through different levels using both abiotic and biotic components. Each of these levels is defined according to its major role of primary producers, primary and secondary consumers, and decomposers. Primary producers are the bottom level that supports all of the other levels. This level consists mainly of plants that use sunlight to make food (photosynthesis), which provides energy for the consumer’s metabolic functions and growth. The upper levels are unable to make their own food so they must depend on the level below them for energy. All of the upper levels are directly or indirectly dependent on the primary producers.
- Primary Producers
- Primary and Secondary Consumers
As energy flows through the ecosystem it determines the relationships of the different levels. Unlike materials such as water, oxygen carbon, phosphates and nitrates that are recycled, energy is lost at each level. Each successive level contains less energy, less organic material and fewer numbers of organisms. As a rule, about 90 percent of the available energy for any level is lost through heat, movement and other metabolic activities. Only 10 percent, on average, is available for transfer to the next level.
Activity 1 will demonstrate the flow of energy through an ecosystem. Students will demonstrate how energy takes a one-way course and is dissipated at every level.
Activity 2 will demonstrate how the flow of energy in an ecosystem is much more complex than a simple food chain as demonstrated in Activity 1. Students will determine how all things are connected using energy flow in a food web.
- Gather a boxful of packing peanuts, leaves or popcorn. Note: Packing peanuts work best because they aren’t quite as messy and can be re-used.
- Photocopy food chain cards on heavy stock paper (you may want to laminate them for re-use). Punch two holes at the top two corners of the cards and tie a piece of string in the holes that is long enough to go around a student’s neck.
- Photocopy the “Food Web” worksheet – 1 for each student.
- Mark 3’ x 3’ plots in the garden where students can work in small groups. Students should work in groups of 3 or 4.
Doing Activity 1 -How does energy pass through a food chain?
In the classroom
- Ask the students if they know where all of the energy in the world originates? (the sun) How is the sun’s energy made available for plants’ and animals’ use? (green plants make food through photosynthesis.) How do green plants make food? (green plants use carbon dioxide (CO2) from the air, water (H2O) and sunlight (E) to produce sugar (C6H12O6) and oxygen (O2).
Ask the students if green plants are the only organisms that can make their own food, as well as providing food for animals? What word would they use to describe what the plants are doing? Green plants are producers. They produce all the food energy available for animals.
- Ask if anyone can name an animal that eats plants? Is there any animal that might eat the plant-eater? Both these animals consume food energy, one from the plant, the other by eating a plant-eater. They are called consumers. primary consumers eat plants and secondary consumers eat plant-eaters. What happens to plants and animals when they die? They are consumed or broken down by organisms called decomposers. Decomposers are important because they recycle nutrients for use by plants.
- When linked together the producers, consumers and decomposers transfer the sun’s energy from plants to animals. These transfers can be shown through a food chain. A food chain links together the sun, plants and animals that depend on one another for food. Have students construct a simple food chain.
- Ask students if they think that plants and animals capture all of the energy that comes from the sun. Explain that to demonstrate what happens to the energy as it flows through a food chain, you are going to go outside and have them participate in a demonstration. Divide the class into food chains of at least four members. Place tags on them describing what organism they are in the food chain. Discuss what order their food chain should flow starting with plants. Take them outside.
- Line up members of each group several yards apart in a line. They should be in the order that they appear in the food chain.
- A box full of packing peanuts, leaves, or popcorn will represent the food energy in the food chains. Explain to the students that each sun in the perspective food chain will take an overflowing armful of “energy” from the box. At the command “”Go” the suns (holding the energy in their arms) will race to the plants in their food chain and transfer the energy into the plants arms. Some energy will fall to the ground. That’s OK. That’s what is supposed to happen. The plants, in turn race with the energy to the next consumer and transfer the energy. Each food chain member in turn receives the energy and transfers the energy to the next food chain member until the end of the food chain is reached. The decomposer should hold on to the energy that is left. Students should be encouraged to transfer the energy to the end of the food chain as quickly as possible.
- Have each sun take an overflowing armful of energy and give the command “GO”. After the relay race is over have the students remain in place in their lines. (On the ground should be progressively smaller piles of energy and the person at the end of the food chain should have only a handful of energy left. What happened to the energy as it was passed through the food chain? How would plants and animals use the energy that was lost? (respiration, transpiration, reproduction, digestion, physical movement, heat, etc.) What happens to the energy that is not lost? (used for growth or stored as fat) Ask students if they think more energy is stored or used at each level? (ninety percent of the useable energy is lost in each transfer of energy)
In the classroom
- Now students have seen how energy is transferred, used and lost in a food chain. They also learned that at each link in the food chain, 90 percent of the energy is lost. Ask students what level of the food chain receives the most energy? (plants) The least? (top level consumers) Based on this information would students expect there to be more grass or hawks in the environment?
In order to demonstrate this concept, students will need to do some math. Give each student a paper and pencil.
- In this example, all animals and plants are equal to 10 units of energy. Let’s say for example that one hawk needs 10 units of energy to survive in one month. If the hawk eats shrews and each one is 1/10 of the energy needed by the hawk, how many shrews would the hawk need to eat that month? (10)
One shrew also needs 10 units of energy to survive. It only gets 1/10 of the energy it needs from one grasshopper. How many grasshoppers would one shrew need to eat? (10).
So, 10 shrews would need how many grasshoppers to survive? (10 x 10 = 100).
OK, now a grasshopper only gets 1/10 of its energy from a plant. How many plants would a grasshopper need to eat to survive? (10) If there are 100 grasshoppers, how many plants do they need to survive? (100 x 10 = 1,000)
On the board, write the names of the plants and the animals and the numbers of them in the food pyramid next to each name.
Ask students what would happen to the food pyramid if one level was destroyed in some way? For example, if all of the grasshoppers were destroyed by a pesticide, what would happen to the pyramid? Use other examples and discuss.
Doing the Activity 2 - From Food Chain to Food Web
In the classroom
- The flow of energy in the environment is much more complex than a simple food chain that was demonstrated in Part 1. Ask students how it is more complex. (all things are connected in some way) To experience this concept more clearly, students will go outside to explore the flow of energy in the garden.
- Divide the students into small groups that will work together outside.
In the garden
- Give each student a “Food Web” worksheet, a lapboard and a pencil. Tell them that their group is going to be assigned an area of the garden where they will have to list on their worksheets all of the living organisms they find.
- Assign each group to a 3’ x 3’ square area in the garden and have them begin to record the organisms. If they know the name of the plant or animal have them record that. If they do not know the names of the plants or animals, they should list them on their sheet as Plant #1, Plant #2, Animal #1, Insect #1, etc. Give them approximately 15 minutes to record as many organisms or signs of organisms (footprints, chewing, etc.) that they can find. Remind them to look in the soil, under leaves, and other hidden places where creatures may be hiding.
When the students are through with their search, have them replace the ground cover so that it looks like it was never disturbed.
- Regroup the students and have each group record their findings. As each group reports, all students should add plants and animals they do not have listed on their worksheet.
- After everyone reports ask how many plants were found. Were there more larger plants or smaller plants (trees/bushes vs. flowers)? Ask how many animals were found. As students look at their worksheet, ask if anyone sees a connection between two of the organisms. (a grasshopper eats grass). Tell the students to draw a line across the center of the starburst to connect the two organisms.
- Break the students back into their small groups. Have them work together to make as many connections as possible across the center of the starburst. An organism may be connected to more than one other organism.
- Regroup the students again. Ask them if there was anything on their list that was not connected to something else? Ask students what the center of the starburst looks like now that everything is connected? (a web) And what type of energy is being passed from one organism to another? (food energy) So, what do they think the name of this type of web is called? (a food web) A food web is nothing more than a number of food chains all linked together.
- Discuss what would happen if one of the plants or animals disappeared? With a crayon, colored pencil or marker, have students draw a line to the other organisms that are affected. From there they should draw lines to the organisms that are affected again. Have them continue until they cannot connect anything else. Discuss the outcome. (everything becomes affected)
- Observation of students during activities
- Evaluation of Worksheets
- Participation in Discussions
Have students trace the food chains that bring them their school lunches, snacks or other meals. Put the food chains together to make a food web.
- Pennsylvania Department of Environmental Resources, Activities for Environmental Learning, 1989
- Council for Environmental Education, Project Wild, K-12 Curriculum & Activity Guide, 2000
- Borror & White, A Field Guide to Insects, Houghton Mifflin Company Boston, 1970
- Merritt, Joseph, Guide to the Mammals of Pennsylvania, University of Pittsburgh Press, 1987