By Debbie Breeding, teacher, Palms Ave. School, LAUSD
and Esther Zack, teacher, LAUSD/LAEP

Background:

Food Chain

Every living thing needs energy to remain living. A food chain is a simplified look at how that energy is transferred from one living thing to another. All energy comes directly or indirectly from the sun. Green plants convert solar energy to chemical, and are therefore called PRODUCERS. Animals that eat some form of plants are called PRIMARY CONSUMERS. Animals that eat such an animal are called SECONDARY PRODUCERS. Animals that eat these animals are called TERTIARY PRODUCERS. The level an animal is on depends on the particular "chain". DECOMPOSERS break down stored energy in once living things.

Food Pyramid

A food pyramid is a model that demonstrates how much energy is needed to sustain a particular living thing.

Red-tailed hawk

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Food Web

A food web demonstrates the complexity of the interdependence of living things within a habitat. It is based on the food pyramid, and the different plants and animals any particular animal may consume. It may demonstrate the role of decomposers.

Concept: 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.

Materials:

• Namecards of chaparral plants, animals, and sun (enough for your class)
  
• Ball of yarn

Directed Lesson:

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-eating animal. Be sure the "plant" holds onto the yarn before tossing the ball.

The plant eater 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.

Snip off the yarn and give the ball back to the sun. Start the sequence again. 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 oppossum eat nearly everything--plants, animals, and human foods.

Variation:

Have one link in the chain drop the yarn indicating its death due to pesticide comsumption. Students should hypothesize what happens to the other ends of that yarn. For example, the field mouse could have eaten some poisoned bait. The plants it eats would possibly go unchecked. The snake that normally would eat the mouse has to find another source of food, since it eats live prey. Also, if the snake eats a live contaminated mouse, it will accumulate the same poison in its system, thereby affecting the hawk that eats the snake.

Extensions:

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 insect marks on plants such as chewed leaves 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.

In the Chaparral

In an Oak Woodland

In the Grassland