BioEd Online

Teacher Background

Environments, such as oceans, forests, lakes, and deserts, are homes to different communities of organisms. Within each distinct environment, plants, animals, and other living things must find ways to obtain water, food, and other necessary resources. Different kinds of organisms have different needs. As seen in the previous activities, plants need air, water, nutrients (usually from soil), and light. Animals need air, water, and food.

All animals depend on plants and other producers. Some animals eat plants for food. Other animals eat animals that eat the plants, and so on. Some organisms even feed on waste and dead material. The general sequence of who eats whom in an ecosystem is known as a food chain. Energy is passed from one organism to another at each step in the chain. Most organisms, however, have more than one food source. Thus, a web, which depicts all of the different foods eaten by each animal, is a more accurate model of interactions within an ecosystem.

This activity lets students construct possible food webs for different ecosystems, as they learn about the roles of different kinds of living organisms.

Objectives and Standards

Concepts

• Producers make all the molecules they need from simple substances and energy from the sun.

• All other living things depend on producers for food.

• Living things that must eat other organisms as food are known as consumers.

• Food webs show all of the different interactions among producers and consumers in an ecosystem.

Science, Health, and Math Skills

• Inferring

• Integrating information

• Drawing conclusions

Materials and Setup

Materials per Student Group (see Setup)

• set of crayons: one each of blue, green, red, and yellow

• set of Ecosystem Cards representing one ecosystem

• sheet of white construction or drawing paper, 9 in. x 12 in.

Setup

1. Make copies of the six sets of Ecosystem Cards for students in advance. Each group of students will receive one set of the cards.

2. Have students work in teams of 4.

Procedure and Extensions

1. Remind students of the previous activity in which they explored plants that people eat. Ask, Do people only eat one kind of food? What kinds of food do people eat? Explain to students that most other animals also have several food sources, although not all animals are omnivores (eat plants and animals).

2. Discuss with students the different kinds of consumers:
   
   Herbivores (primary consumers) feed on plants and other producers. Cows, camels, caterpillars, and aphids are herbivores.
   
   Carnivores (secondary consumers) feed on other animals. Most consumers are animals, but a few are plants that trap and digest insects. There can be several levels of carnivores in a food chain. Lions, owls, and lobsters are carnivores.
   
   Omnivores eat plants and animals. Pigs, dogs, humans, and cockroaches all are omnivores.
   
   Decomposers and scavengers feed off the dead remains and waste of other organisms at any step along a food chain. Scavengers, such as vultures and flies, feed on remains of animals that have been killed or that die naturally. Decomposers live off waste products and parts of dead organisms. Many kinds of bacteria and fungi (molds and mushrooms) are decomposers. The decomposers themselves are important food sources for other organisms that live in soil, such as worms and insects.

3. Give each group of students a different set of Ecosystem Cards. Each set consists of six cards depicting producers and consumers typically found within a given environment.

4. Have students in each group read the information on the cards.

5. Ask students to identify which organisms are the producers in their ecosystems. Next, have the members of each group identify which cards represent different kinds of consumers (herbivores, carnivores,and scavenger/decomposers).

6. Once students have identified the producers and different kinds of consumers in their ecosystems, have them discuss “who might eat whom” among the organisms depicted on their cards. For example, in the Freshwater Pond set of cards, the bluegill fish (carnivore) might eat dragonfly nymphs and snails. The snail (decomposer/scavenger) might eat the green algae, as well as waste or dead body parts from all of the other organisms in the system. Have students consider possible food sources for each of the organisms in their ecosystem.

7. Give each group a sheet of drawing paper. Instruct students to write the names of each of the organisms in their ecosystems around the edges of the sheet. Have them write the names of the producers in green, the herbivores in yellow, the carnivores in blue, and the decomposers and scavengers in red.

8. Next, have students draw lines to connect each consumer to all of its food sources. They will find that there are many ways to connect even as few as six organisms within an ecosystem.

9. Encourage students to think about the complex relationships within ecosystems by asking questions such as, What would happen if there were no producers in your ecosystem? No decomposers? Where would humans fit in your food web? Do humans also depend on many different plants and animals?

Extensions

• Have students (individually or in groups) draw pictures of their ecosystems, including the organisms they used to construct their food webs.

• Have students conduct additional research about the ecosystems and/or organisms that they used for the food webs by consulting resources available at the library, on the internet, or from sources such as DVD/CD collections.

Handouts and Downloads