Food Webs & Energy Flow
How energy enters ecosystems and moves through producers, consumers, and decomposers
Description
A 30 minute Grade 8 lesson on how energy enters ecosystems (mainly sunlight), how producers convert it to chemical energy, and how energy is transferred and lost as heat through a food web.
Learning Objectives
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Explain how energy enters most ecosystems and how producers convert light energy into chemical energy.
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Interpret arrows in a food web as the direction of energy transfer and identify producers, consumers, and decomposers.
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Describe why less energy is available at higher trophic levels and connect this to smaller populations of top predators.
Content Preview
Preview of the PRISM content
## Essential question How does energy enter an ecosystem, and how does it move through a food web?
## Big idea (accuracy check) Energy is not created by ecosystems. Energy mostly enters as sunlight and is transformed into chemical energy stored in food. As organisms use energy, much of it leaves the ecosystem as heat.
### Vocabulary - Producer (autotroph): makes its own food (usually using sunlight). - Consumer (heterotroph): gets energy by eating other organisms. - Decomposer: breaks down dead organisms and waste. - Trophic level: a feeding level in a food web (producer, primary consumer, etc.). - Biomass: the total mass of living material in an area.
### Quick start question (1 minute) Trace the energy in one bite of food back to its original source. (Hint: most paths start with the Sun.)
Most ecosystems start with producers that capture sunlight and store that energy in sugars. This converts light energy into chemical energy.
Energy flows one-way: in as sunlight, out as heat. Matter (atoms like carbon, nitrogen, and water) can be recycled through decomposers and the environment.
## Food chains and food webs - A food chain is one path of energy flow. - A food web shows many connected paths.
### How to read arrows In food webs, arrows show the direction that energy moves: from the organism being eaten to the organism that eats it.
Example: If a rabbit eats grass, the arrow goes grass -> rabbit.
## Why there are fewer top predators Organisms use energy to stay alive: moving, staying warm, growing, and reproducing. Much of that energy becomes heat during respiration and cannot be used by the next trophic level.
A common rule of thumb is that only about 10 percent of energy stored as biomass transfers to the next trophic level. The exact percent varies, but the pattern is consistent: less energy is available higher up.
- Identify the main source of energy for most ecosystems (sunlight).
- Explain the role of producers, consumers, and decomposers in energy transfer.
- Read a food web arrow as energy moving from food to eater.
- Explain why energy decreases at higher trophic levels.
Assessment Questions
5 questionsIn most ecosystems, what is the original source of the energy stored in food?
In a food web, an arrow from grass to rabbit shows:
Match the term to its role in energy flow:
Photosynthesis converts ______ energy into ______ energy stored in food.
Explain why energy pyramids get narrower toward the top (why there is less energy for top predators). Use the words heat and respiration in your answer.
Standards Alignment
Resource Details
- Subject
- Science
- Language
- EN-US
- Author
- PRISM Learning Objects Generator
- License
- CC-BY-4.0
- PRISM ID
- food-webs-energy-flow-g8