Phenomenon
All ecosystems rely on continual energy input from the sun. It takes a lot of producers to support just a few top consumers.
Question
Why do ecosystems need a continuous supply of sunlight? How is energy transferred up the food chain from producers to top consumers?
Model Ideas
- The sun is the original source of energy for an ecosystem
- Because of the interdependence of organisms within an ecosystem, the products of photosynthesis provide matter that can be used for energy (both directly and indirectly) for all organisms within the ecosystem.
- Organisms are made of matter that can be converted to release energy, so when they are eaten, the “eater” gets that matter and potential energy, which is then used for its own processes.
- Once the energy is used, it is released as heat and is NOT recycled like matter. Any matter that is not converted during cellular respiration remains in the organism and the potential energy in those molecules is available to the next organisms up the food chain.
- Typically, only about 10% of the potential energy in the system at one level is available to the next level up the food chain.
Overview
Transition in: We established in Matter Cycles that matter in the Ecosphere is recycled but is there anything we need to supply in order to keep the organisms alive? What would happen if we put the Ecosphere in a drawer?
Students usually know without sunlight all organisms in the Ecosphere (and Earth) will die, even if they can’t explain why. In the previous model we focused on matter. In this model our attention shifts to energy. Why does energy in the form of sunlight need to be constantly supplied? We know that energy can’t be created or destroyed, so where does that energy go? To explore this, students consider first what is going on in the ecosphere and then examine biomass patterns in ecosystems. The goal is for students to figure out that most food eaten by organisms is used to obtain energy for their life activities and therefore lost to the ecosystem. Only the food that is converted to new body tissue is available to the next organism up the food chain.
NOTE: This is a logical place to touch back on biodiversity. Now that we understand more about the interdependence of organisms we can discuss the importance of biodiversity in a better light. How might the loss of a species impact other organisms in an ecosystem - the ocean, a pond, the Ecosphere, Isle Royale?
Transition out: We know a lot about what organisms need to have and do in order to survive. But is individual survival enough to insure species survival? Looking at our natural selection model we remember the continuation of a species is only possible if those who survive also reproduce and pass their traits to offspring.
1. First we return to the ecosphere, review what we’ve already figured out and then consider the role of sunlight in maintaining it. We come up with a driving question.
We noticed that the energy in the ecosphere is somehow different from the matter. It has to be continuously supplied. We came up with a driving question about that.
2. Students generate an initial model to explain why the ecosphere needs a continuous supply of energy when it can recycle the matter inside of it. Now that students have identified the phenomenon and come up with a question to explore, they will generate an initial model, based on prior knowledge, that will help them to explain why the ecosphere needs to be in the light. Students should already have model ideas for explaining much of this, but a key component that they may not have made a connection to is that energy is “lost” to the environment as heat in each chemical reaction. This is a quick, initial model discussion. They will go more in depth in subsequent learning segments.
We generated an initial model to explain our question about the phenomenon of energy and the ecosphere.
3. Students further explore their models ideas in order to account for energy lost as heat to the environment through cellular respiration, and that some energy is stored in tissue. Students participate in an activity that is an analogy for heat loss within an ecosystem. They then return to the driving question and revisit their model.
We further explored energy related ideas in food chains and participated in an activity that helped them to better understand what is meant by “heat loss” in an ecosystem. We finalized our model and answered the driving question.
4. We explore an additional application of the model in order to solidify our ideas. There is a common assertion that it is more environmentally friendly to is to “eat lower on the food chain”. Students will consider if this seems to be supported by our model or not.
We applied our model to consider human impacts.
Download Resources
| Attachment | Size |
|---|---|
| mber_energyflowvfeb2018.zip | 808.96 KB |