• When students are working on the Classifying Cards activity, circulate among the small groups and ask questions to check for students’ understanding of the trophic level concepts.

• Collect and check students’ Scrambled Food Chain handout, as well as their paragraph describing a food chain.

• Circulate throughout the room and monitor students’ progress creating food webs in small groups. Also, check written explanations about why food webs are a better model than food chains.

Part 1: Energy Flow through Food Chains

As a whole-class activity, generate a list of dinner food options (e.g., chicken, spinach, rice, steak, salmon, and carrots). Have each student choose what s/he would eat for dinner. Then have students classify the food items into a chart with the headings “Eats,” “Get Eaten,” and “Both.” Introduce the concepts of autotrophs and heterotrophs and apply them to the chart. Explain that autotroph is a synonym for producer and heterotroph is a synonym for consumer (producer and consumer should be familiar terms).

Present students with a model food chain, such as:

Grass → Grasshopper → Toad → Snake → Bacteria

Explain that most food chains fit the general pattern:

Autotrophs (Producers) → Herbivores (Primary Consumers) → Carnivores (Secondary and Tertiary Consumers) → Decomposers

Have students write the pattern in their notes, and define terms as needed. Explain that each level of a food chain is called a trophic level. Ask students where the grass gets its energy (i.e., the Sun) and what the arrows represent (i.e., the flow of energy through the food chain). Note that decomposers are not always included in food chains, and they can fit into a food chain at any level. Explain that decomposers can fit at any level because they break down waste material and dead organisms at every trophic level. Also note that detritivore is a subcategory that is sometimes used interchangeably with decomposer; examples are earthworms and crabs.

Activity: Classifying Ecosystem Roles

Hand out one set of the Classifying Cards (S-B-2-1_ Classifying Cards.docx) to each small group of students. Have each group sort the organisms into three piles, producers, consumers, and decomposers. Then have the groups further sort the consumers into piles representing herbivores, carnivores, and omnivores.

Provide students with other examples of food chains. Ask students to identify the trophic levels in each of the food chains. Discuss why there are more producers than consumers in food chains.

Activity: Scramble Food Chain

Divide students into small groups, and give each team the Scrambled Food Chain handout (S-B-2-1_ Scrambled Food Chain.docx). Have students complete the handout together, then share answers as a whole class (S-B-2-1_ Scrambled Food Chain KEY.docx). Note: See the Marine Food Chain Web site in the Related Resources section for more information about feeding relationships between marine organisms.

Have each student write a paragraph describing feeding relationships in one of the food chains from this lesson. The paragraph should include the terms energy, producers, and consumers in the description.

Part 2: Food Webs

Ask students why food chains are a good model of feeding relationships in ecosystems. Elicit that they show the transfer of energy from one organism to another. Tell students that food chains are a very simple model that doesn’t include all the possible feeding relationships between organisms.

Whole-Class Activity: Food Web

Demonstrate this concept by having students brainstorm organisms that can be found in an open field (e.g., fox, hawk, snake, mouse, frog, grasshopper, and rabbit.) Write the organisms on the board (spread out). Have student volunteers draw arrows to show which animals eat each other in this field ecosystem. Check to ensure that students’ arrows point in the direction that the energy flows. Students should see how complex even a simple food web can be, because each predator can have more than one type of prey, and each type of prey can be eaten by different predators.

Activity: Food Webs

If Internet access is available:

Have students view the short video, Energy Flow in the Coral Reef Ecosystem (see Materials section for this lesson.) After they view the video, have them identify various feeding relationships and identify producers and consumers from the coral reef ecosystem.

Then, have small groups of students complete the Food Webs (interactive activity) (see Materials section for this lesson.) Assign each group one of the four food web choices. Monitor students as they work on this activity, asking questions about the feeding habits of the organisms in the food web.

Additional online activities on food webs are available in the Related Resources section.

If Internet access is not available, divide students into small groups and redistribute the unlined paper and the Classifying Cards (S-B-2-1_ Classifying Cards.docx). Have each small group of students arrange the classifying cards into a food web on the sheet of unlined paper, drawing arrows on the paper to indicate the flow of energy. Monitor students as they work on this activity, checking the direction of the arrows and asking questions that require students to explain the trophic levels in the food web (S-B-2-1_ Classifying Cards KEY.docx).

Have each student write an explanation in his/her notes on why food webs are better than food chains for showing ecosystem interactions.

Extension:

• For Part 1, assist students by having them create a concept map using the following terms: trophic levels, autotrophs, producers, herbivores, primary consumers, carnivores, secondary consumers, tertiary consumers, and decomposers.

• Alternatively, display a list of organisms that would be found in a specific ecosystem, such as the desert. Guide students in writing “P” or “C” next to the organisms to label the producers and consumers. Then, have them write “H,” “C,” or “O” next to the organisms to label herbivores, carnivores, and omnivores. Help them make a food chain by connecting a producer, herbivore, and a carnivore.

• Challenge students who are performing above and beyond the standards by having them research other feeding relationships among marine organisms and creating an additional food chain (see the Marine Food Chain Web site in Related Resources).

• For Part 2, have students who may need opportunities for additional learning copy the food web from the board into their notes. Remind students that the arrows point in the direction of energy flow. For the online activity, guide students in completing it step-by-step with you. For the classifying cards activity, remove a few of the cards to create a simpler food web.

• Challenge students who are performing above and beyond the standards to add extra organisms to the food web that they create in Part 2.