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Food Chains and Webs

All living organisms depend on one another for food. By reviewing the relationships of organisms that feed on one another, this lesson explores how all organisms— including humans—are linked. If students understand the relationships in a simple food chain, they will better understand the importance and sensitivity of these connections, and why changes to one part of the food chain almost always impact another.

Grade level: 4-8 grades

Performance Expectations:

  • MS-LS2-1 Ecosystems: Interactions, Energy and Dynamics. Analyze and interpret data to provide evidence for the effects of resource availability on organisms and populations of organisms in an ecosystem.
  • MS-LS2-2 Ecosystems: Interactions, Energy and Dynamics. Construct an explanation about how the different parts of the food chain are dependent on each other.
  • MS-LS2-3 Ecosystems: Interactions, Energy and Dynamics. Develop a model to describe the cycling of matter and flow of energy among living parts of the food chain.
  • MS-LS2-4 Ecosystems: Interactions, Energy and Dynamics. Construct an argument, supported by evidence gathered through observation and experience, showing how changes to physical or biological components of an ecosystem affect populations.
  • MS-LS2-5 Ecosystems: Interactions, Energy and Dynamics. Evaluate competing design solutions for maintaining biodiversity and ecosystem services.
  • MS-ESS3-3 Earth and Human Activity. Answer questions about how pollution affects food chains by applying scientific principles to design a monitoring plan for minimizing the human impact on the environment.

For alignment, see: Food Chains and Webs NGSS Summary

Lesson Objectives

  • Describe the difference between herbivores, carnivores and producers.
  • Answer questions about the interdependence of herbivores, carnivores and producers as members of a food chain.
  • Answer questions about how pollution affects food chains.

Background

A food chain is a simplified way to show the relationship of organisms that feed on each other. It’s helpful to classify animals in a simple food chain by what they eat, or where they get their energy.

Green plants, called producers, form the basis of the aquatic food chain. They get their energy from the sun and make their own food through photosynthesis. In the Great Lakes, producers can be microscopic phytoplankton (plant plankton), algae, aquatic plants like Elodea, or plants like cattails that emerge from the water’s surface.

Herbivores, such as ducks, small fish and many species of zooplankton (animal plankton) eat plants. Carnivores (meat eaters) eat other animals and can be small (e.g., frog) or large (e.g., lake trout). Omnivores are animals (including humans) that eat both plants and animals. Each is an important part of the food chain.

In reality, food chains overlap at many points — because animals often feed on multiple species — forming complex food webs. Food web diagrams depict all feeding interactions among species in real communities. These complex diagrams often appear as intricate spider webs connecting the species.

This lesson demonstrates that changes in one part of a food chain or web may affect other parts, resulting in impacts on carnivores, herbivores, and eventually on producers. An example of this might be the harmful effects of pollution. The point that should be made is that when something disrupts a food web, humans should try to understand and minimize the disturbance. Students should also come to recognize that humans, too, are part of this complex web of life.

Food Chains and Food Webs – Parts and Pieces

Food Chains

  • Producers
    Plants form the base of Great Lakes food chains. They’re called producers, because they make their own food by converting sunlight through photosynthesis. They also act as food, providing energy for other organisms. In the Great Lakes, most producers are phytoplankton, or microscopic floating plants. An example of phytoplankton is green algae. Large rooted plants, another type of producer, provide food and shelter for different organisms, fish and wildlife.
  • Primary Consumers
    The next level in the food chain is made up of primary consumers, or organisms that eat food produced by other organisms. Examples of primary consumers include zooplankton, ducks, tadpoles, mayfly nymphs and small crustaceans.
  • Secondary Consumers
    Secondary consumers make up the third level of the food chain. Secondary consumers feed on smaller, plant-eating animals (primary consumers). Examples of secondary consumers include bluegill, small fish, crayfish and frogs.
  • Top Predators
    Top predators are at the top of the food chain. Top predators eat plants, primary consumers and/or secondary consumers. They can be carnivores or omnivores. Top predators typically sit atop the food chain without predators of their own. Examples include fish such as lake trout, walleye, pike and bass, birds such as herons, gulls and red tailed hawks, bears—and humans!
  • Food Webs
    In reality, many different food chains interact to form complex food webs. This complexity may help to ensure a species’ survival in nature. If one organism in a chain becomes scarce, another may be able to assume its role. In general, the diversity of organisms that do similar things provides a type of safety, and may allow an ecological community to continue to function in a similar way, even when one species becomes scarce. However, some changes in one part of the food web may have effects at various trophic levels, or any of the feeding levels that energy passes through as it continues through the ecosystem.

At the base of the aquatic food web are:

  • Plankton
    Plankton are microscopic plants and animals whose movements are largely dependent upon currents. Plankton are the foundation of the aquatic food web. Plankton are vital in the food supplies of fish, aquatic birds, reptiles, amphibians and mammals.
  • Phytoplankton
    Plant plankton are called phytoplankton and may be single cells or colonies. Several environmental factors influence the growth of phytoplankton: temperature, sunlight, the availability of organic or inorganic nutrients, and predation by herbivores (plant eaters).
  • Zooplankton
    Animal plankton are called zooplankton. Zooplankton can move on their own, but their movement is overpowered by currents. Zooplankton may be herbivores or plant-eaters (eat phytoplankton), carnivores or meat eaters (eat other zooplankton) or omnivores, which eat both plants and animals (eat phytoplankton and zooplankton). 

 

Activity

  • Linking the Chain
    Summary: Students work with paper cutouts to learn about the parts of a food chain, specifically herbivores, carnivores and producers.
    Time: 30-60 minutes of class time