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

What is the Food Chain? A food chain is a sequence of transfer of matter and energy through food, from one organism to another. Due to the fact that most consumers in a food chain feed on more than one type of plant or animal, an intertwined network of the food chain is often found.

Performance Expectations:

A food chain shows how each living thing gets food, and how nutrients and energy are passed from creature to creature. Food chains begin with plant-life, and end with animal-life. Some animals eat plants, some animals eat other animals. A simple food chain could start with grass, which is eaten by rabbits. When animals eat, the energy in the food passes along a food chain. The first link in the chain is a plant. Plants are called producers because they make their own food. Animals that eat plants are known as primary consumers. A food chain always starts with a producer. This is an organism that makes its own food. Most food chains start with a green plant, because plants can make their food by photosynthesis.

• 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 chainis 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.

Examples Of Food Chains

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).

Assessment & Standards

See separate document: Lesson Assessment, State of Michigan Content Expectations and National Benchmarks (PDF)

Activity

Food Chains For Kids

• 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

The term food chain refers to a series of linked feeding relationships between living things in an ecosystem. More specifically, a food chain describes the order in which matter and energy in the form of food are transferred from one organism to another. Because most organisms eat more than one type of plant or animal, an organism may belong to more than one food chain. As a result, the food chains in an ecosystem overlap and intertwine to form a complex food web.

Food chains are organized across several trophic, or feeding, levels. Organisms at each level feed on organisms from the level below and are in turn eaten by organisms from the level above. A typical grassland food chain would extend from grasses to rabbits (which eat grasses), to snakes (which eat rabbits), and to hawks (which eat snakes).

Trophic Levels

Organisms at the first level in a food chain are called producers. These are organisms that can make their own food. They use photosynthesis to convert light energy from the Sun into the chemical energy of food. Plants, algae, and phytoplankton (plantlike plankton) are examples of producers.

Organisms in the remaining trophic levels are called consumers. The organisms at the second level of the food chain are called primary consumers. These are organisms that eat producers. Primary consumers in a grassland ecosystem might include rabbits and bison, as well as insects and birds that feed on vegetation. The primary consumers in a pond ecosystem might include snails, caterpillars, muskrats, and beavers. In many marine ecosystems, zooplankton (animal-like plankton) such as copepods and krill are the main primary consumers.

The third level of the food chain contains secondary consumers. These are animals that eat primary consumers. Grassland secondary consumers might include coyotes and snakes. In many marine environments, seals, squid, and fish fill this role. Secondary consumers in the Antarctic ecosystem include blue whales and penguins, among other animals.

Many food chains have a fourth level that contains tertiary consumers—animals that eat secondary consumers. Hawks, badgers, and wolves are tertiary consumers in some terrestrial ecosystems. In marine environments, this role is played by large fish, jellyfish, seals, turtles, small sharks, dolphins, and whales, among others.

Some very large ecosystems may have a fifth level that consists of quaternary consumers. These are animals that eat tertiary consumers and, in some cases, secondary and even primary consumers.

The fundamental source of energy in almost all ecosystems is light energy from the Sun. This energy is converted by producers to the chemical energy of food, which is then transferred from one trophic level to another.

Most of the energy—about 90 percent—that enters a trophic level is used up by the organisms at that level. They use this energy to power the normal activities of life, so it is “lost” from the food chain as heat. The energy that is not used for these processes is stored in the organism’s tissues. It is then passed to the next trophic level when the organism is consumed. This means that the total amount of energy decreases from one trophic level to the next as it moves up the food chain.

Most food chains have only three or four trophic levels because there is not enough energy remaining at the top of the chain to support more levels. The grassland food chain described earlier contains four trophic levels: producers (grass), primary consumers (rabbits), secondary consumers (snakes), and tertiary consumers (hawks). A wetland food chain might have a similar structure. It might consist of bulrushes (producers), beetles (primary consumers), frogs (secondary consumers), and herons (tertiary consumers). However, an ocean food chain might have five levels. It might comprise single-celled algae called dinoflagellates (producers), copepods (primary consumers), sunfish (secondary consumers), small sharks (tertiary consumers), and large sharks (quaternary consumers). (See alsoenergy pyramid.)

Matter is recycled through an ecosystem by decomposers. These are organisms that feed on the tissues of dead or dying producers and consumers. Bacteria and fungi are common decomposers, as are certain types of worms and insects. Decomposers are active at every trophic level. They break down dead tissues into nutrients such as phosphorus, carbon, and nitrogen. The nutrients are then released into the soil, where they can be taken up by plants and recycled again through the food chain.

Food Webs

Natural ecosystems have many different types of producers and consumers, all of which get nutrients from more than one source. As a result, each organism in an ecosystem may belong to multiple food chains. The food chains of the ecosystem intertwine and overlap to form a complex of interactions called a food web. A food web is a model of the feeding relationships between all of the different types of organisms in an ecosystem.

A food web is useful for understanding the complex connections across trophic levels in an ecosystem. Food webs show not only how different organisms get energy but also how organisms affect each other through competition and predation. In the simplified grassland food web shown above, grasshoppers and rabbits both feed on the same type of plants, meaning they compete for that resource. Coyotes and snakes (secondary consumers) compete for both rabbits and grasshoppers (primary consumers). However, coyotes also feed on snakes—another secondary consumer. These relationships illustrate the complex nature of a food web. Organisms at one trophic level may feed on organisms at multiple levels. In this example, coyotes prey on snakes—organisms at their own trophic level—and also compete with them for resources at lower trophic levels. Similarly, hawks (tertiary consumers) feed on snakes (secondary consumers) and also on rabbits (primary consumers).

Animals at the top level of a food web are sometimes called top predators. They are the dominant predators in their ecosystem and do not have natural enemies. Brown bears are the top predators in some northern forests of North America. Killer whales are top predators in the Antarctic marine ecosystem.