5. Food Chains

Summary
Students review the concepts of food chains and the roles of organisms in a food chain through a simple card sorting activity. Cards representing different individuals in a California ecosystem are first sorted by herbivore, carnivore, dentrivore, and omnivore, then are reordered to create several food chains. In addition, students begin to understand the idea of a food pyramid – since all living things use energy to move, reproduce, respond to the environment and grow, less energy is available to pass on at each link of the food chain.

Objectives
Can define and construct a food chain.
Can identify the role of organisms within a food chain.
Can trace the path of energy through a food chain.
Can build a food pyramid and explain how it functions in terms of energy transfer at each level.

Vocabulary
Food chain
Produce
Consumer
Herbivore
Carnivore
Dentritivore (or Decomposer)
Omnivore
Food pyramid

Attachment Size
5food_chain.doc 49.5 KB
food_chain_cards.pdf 230.04 KB
food_pyramid_overhead.pdf 251.95 KB

5. Food Chains - Logistics

Time
45-50 minutes

Grouping
individual

Materials

  • 1 copy of organism cards for each student 
  • 1 copy of food pyramid overhead for the teacher
  • colored pencils
  • scissors
  • glue sticks
  • optional: envelopes

Setting classroom

5. Food Chains - Background

Teacher Background
This activity teaches students 2 things, 1) it reviews the concept of food chains and the major roles of organisms with a food chain and 2) it illustrates the concept of a food pyramid and the transfer of energy from one organism to the next through the food chain. Most students should be familiar with the concept of a food chain and food pyramid from elementary school science, but it is worth at least one class period to thoroughly review these concepts in preparation for more in depth investigations of food webs, ecosystems, and population change.

Food chains are the most simple arrangement of who eats whom assuming that each organism only eats one thing. Of course, in real life this is not the case. Still, it is useful to consider food webs as tangled food chains; therefore, understanding food chains is an essential prerequisite.

The roles that organisms play within a food chain are very well defined. Producers make their own food through photosynthesis. Consumers eat producers or other consumers and may be divided into 4 major categories: herbivores which eat producers, carnivores which eat herbivores or other carnivores, dentritivores (also called decomposers) which recycle the energy from dead organisms to make nutrients available for producers, and omnivores which eat producers and consumers.

Although it is tempting to emphasize that every food chain begins with the sun as the source of energy on which photosynthesis depends, in fact, not all food chains begin with the sun. Organisms near hydrothermal vents at the bottom of the ocean depend on sulfur as the initial energy source. These bacteria use a process called chemosynthesis, taking hydrogen sulfide and oxidizing it, thereby releasing energy. This is typically far more advanced than middle school classrooms although you may wish to allude to the existence of food chains that do not rely on the sun as the initial energy source. For further information, see RESA has a superb website about life at hydrothermal vents.

The concept of a food pyramid adds a level of complexity to the concept of food chains. A producer uses energy from sunlight to grow, reproduce, and survive. Only a small fraction of that energy can be used by a herbivore that eats that producer. Similarly, that herbivore needs to use energy to grow, reproduce, and survive. A carnivore that eats that herbivore does get some energy from that herbivore but only a small percentage. Another way to think of it is to consider how many seeds a plant produces in its lifetime, how many seeds a chicken consumes in its lifetime, and how many chickens a human will consume in its lifetime. Clearly, energy is used and lost at each level of the food chain. Using a food pyramid to illustrate this concept helps students see this visually.

Student Prerequisites
None.

5. Food Chains - Getting Ready

Getting Ready

  1. Make copies of organism cards for each student.
  2. Make an overhead copy of the food pyramid. If your classroom does not have an overhead projector, you can draw a similar diagram on the board or make a few copies to pass out and for students to share among themselves.
  3. Set out colored pencils, scissors, and glue sticks in an easily accessible area.

5. Food Chains - Lesson Plan

Lesson Plan

  1. Begin the lesson with the question: “What did you eat for dinner last night?" Break responses down into individual ingredients (separate lasagna into pasta, beef, tomatoes, and cheese) and write them on the board.
  2. Once you have a broad sampling, begin categorizing the ingredients into producers, and consumers. Use questions such as:
    • Which of these foods come from plants?
    • Which of these foods don't come from plants? (If mushrooms are on the board, remember that technically mushrooms are fungi not plants!)

    At this point, introduce the idea of producers as plants, or more scientifically, as organisms that make their own food through photosynthesis. Introduce the idea of consumers as animals, or more scientifically, as organisms that eat producers or other consumers.

  3. Break down the consumer category further into herbivore, carnivore, omnivore, and dentritivore (or decomposer). Use questions such as:
    • Of the consumers, which are animals that eat plants?
    • Which are animals that eat other animals?
    • Which eat both?
    • Are there any decomposers? (Mushrooms, crab, shrimp, and lobster are likely to be the only decomposers.)

    Introduce the vocabulary words herbivore, carnivore, omnivore, and dentritivore at this point and give the formal definitions.

  4. Ask students to describe a food chain. As part of this discussion, try to follow one or more of the foods on the board through the food chain. For example, sun -> corn -> cow -> people. All the food chains we will be dealing with in this class have the sun as the initial energy source although you may want to briefly mention the existence of other food chains that do not depend on the sun (see notes in Teacher Background section).
  5. Introduce today's activity. Students should receive a set of organism cards. Their first task is to color code the organisms on their cards by their role in the food chain. Write the color code up on the board: green = producers, yellow = herbivores, red = carnivores, orange = omnivores, blue = dentritivores.
  6. When students begin to finish color coding, have students cut out their cards and begin to organize them into food chains. Definitely tell them that there are multiple food chains. If you want, you can tell them how many. When students have identified a complete chain, they can glue it down on a piece of notebook paper.
  7. With 10 minutes before the end of class, have students stop and clean up. Any work they have remaining can be assigned as homework. Envelopes can be used to contain any cut out cards that have not been glued down yet. In my classes, about 50% had finished the activity at this point. 50% had to bring home work to finish at home.
  8. Once the students have cleaned up and are settled again, put the food pyramid up on the overhead and ask students what they think the picture represents. They should recognize the pictures from their food chain activity. Ask the students why there are more grasses than rabbits and why there are more rabbits than bobcats. Discuss the transfer of energy from one level of the food chain to the next, focusing on how any one organism can't transfer the energy it gets from its food directly to the next organism in the food chain because it needs to use some of that energy itself to grow, reproduce and survive.

5. Food Chains - Assessments

Assessment

  1. Complete the food chain activity started in class.
  2. Pick an ingredient from your lunch today and construct a food chain. Make sure to start with the sun and include yourself. Identify the role of each organism (producer, herbivore, omnivore, etc.).

Going Further

  1. Discuss food chains that do not use the sun as its energy source. NOAA has created a website full of lesson plans for grades 5-12 all about life at hydrothermal vents.
  2. Put food chains together into food webs. See Food Web lesson.
  3. Look for signs of food chains outdoors. For instance, look for animal scat, insect marks on leaves, and animals foraging. Owl pellet dissections are a fabulous way to bring this back into the classroom. Kidwings provides a great online resource for owl pellet dissections.
  4. Bring a rotten log back to the classroom to explore the food chains and mini-ecosystems within. See the Rotten Log Lab Assessment. I used this as an end of the unit assessment tool – which both I and the students enjoyed.

5. Food Chains - Sources and Standards

Sources
The idea for the food chain card game came from Project WILD's book Alaska Ecology available for purchase online for $22. Debbie Breeding's activity Food Chains and Webs provided the information and pictures for the food chain cards. The illustrations on the activity pages are by Paula McKenzie, copied from Mountains to the Sea- A Visitor's Guide to the Santa Monica Mountains and Seashore. Another web resource that provides a similar activity is available from the British Ecological Society. Some of the illustrations on the activity pages are copied from the food chain cards available on their site.

Standards
Grade 6 Ecology (Life Sciences)

5. Organisms in ecosystems exchange energy and nutrients among themselves and with the environment. As a basis for understanding this concept:

a. Students know energy entering ecosystems as sunlight is transferred by producers into chemical energy through photosynthesis and then from organism to organism through food webs.

b. Students know matter is transferred over time from one organism to others in the food web and between organisms and the physical environment.

c. Students know populations of organisms can be categorized by the functions they serve in an ecosystem.

e. Students know the number and types of organisms an ecosystem can support depends on the resources available and on abiotic factors, such as quantities of light and water, a range of temperatures, and soil composition.