Esther Zack, Presenter, Project Inquiry
An ecosystem consists of a community of living things interacting with each other and the environment. Most ecosystems derive their energy directly or indirectly from the sun.
Food chains and food webs represent the feeding patterns of the members of an ecosystem, as well as the flow of energy.
- Namecards of plants, animals, and sun (enough for your class--list included at end of lesson)
- Ball of yarn
- Pass out the namecards to the students. Give the sun the ball of yarn.
- Review with them that the sun is the source of all energy on earth. Ask the student portraying the sun to whom he or she would throw the ball of yarn to begin the food chain (green plant, or producer ). The sun holds onto the end of the yarn and tosses the ball of yarn to a student wearing the name of a plant.Ask the students why the first step of the food chain is plants.
- Now ask the plant person who would get the ball of yarn next (plant eater, or herbivore). Have the plant toss the ball of yarn to a student wearing the namecard of a plant-feeding animal, such as a butterfly. Be sure the "plant" holds onto the yarn before tossing the ball.
- The plant feeder now looks around for something that eats it, and tosses the yarn to that animal (carnivore or omnivore).
- The game progresses as each member of the food chain takes a turn while holding onto the yarn. The sequence stops at the top of the food chain, a predator that has no enemies, such as a hawk.
- Give the ball back to the sun and start the sequence again with the previous participants still holding onto the yarn. Those who participated before can have another turn, thereby illustrating the growth of a food web. An animal usually has more than one source of food. For example, a bird can eat seeds and insects; or a hawk can eat a rabbit or snake. The coyote and opossum eat nearly everything--plants, animals, and human foods.
Have one link in the chain drop the yarn indicating its death due to pesticide consumption. Students should hypothesize what happens to the other ends of that yarn. For example, the butterfly could have fed on a plant that was sprayed with insecticide. Then a bird that eats it in turn could possibly die as a result, or at least begin to build up some of the toxins in its system. The hawk that feeds on that bird will also start to accumulate the contaminant in its system. A similar series of events did happen with the peregrine falcon and bald eagle. The result of their consumption of pesticides led to the laying of eggs with less than viable shells, and therefore they become endangered species.
- Students can make food web/chain mobiles using pictures from magazines, a hanger and string.
- Outdoors, students can explore for signs of food chains in nature, such as finding owl pellets which are a good source of food chain information. Pellets can be purchased commercially and dissected to reveal what the owl has eaten.
- Other signs of food chains are butterfly wings with v-shaped tears on them, signs of a bird taking a bite, or insect marks on plants such as chewed leaves, perhaps by caterpillars or aphid colonies. Buy praying mantids or lady bugs to place on the plants to rid them of insects.
- Sing the song, "I Know an Old Lady Who Swallowed a Fly" and discuss with students if the song represents a true food chain. If they agree it doesn't, ask them how it could be changed to be more scientifically accurate.
Food Chain Links: