To help students understand that almost all kinds of animals’ food can be traced back to plants and that the sun is often the ultimate source of energy needed for all organisms to stay alive and grow.
This lesson is the first of a two-part series on the cycle of life. This series should help enhance student understanding of the flow of matter and energy and the interdependence of life by focusing on food chains and food webs.
Cycle of Life 1: Food Chains focuses on the food chain by helping students understand that almost all kinds of animals’ food can be traced back to plants and that the sun is the ultimate source of energy needed for all organisms to stay alive and grow.
This lesson gives students the opportunity to learn about food chains. Learning about a variety of food chains in various environments will help students learn to identify similarities and differences among them. For example, they will learn that materials can be recycled and used again, sometimes in different forms. Also, they will notice that substances may change form and move from place to place, but they never appear out of nowhere and never just disappear. It is important to note that although this lesson focuses on food chains of what eats what in various environments, it does not focus on labeling the steps in the chain as energy transfer. Transfers of energy at this level are better illustrated in physical systems; biological energy transfer is far too complicated.
Cycle of Life 2: Food Webs extends this thinking by teaching about food webs, focusing on how some insects depend on dead plant and animal matter for food.
This lesson gives students the opportunity to learn about how insects depend on dead plant matter for food. Students explore how various organisms satisfy their needs in the environments in which they are typically found. In addition, they examine the survival needs of different organisms and consider how the conditions in particular habitats can limit what kinds of living things can survive. These activities will help students understand the great diversity of life in different habitats.
Students finishing the second grade should understand that plants and animals need water to survive. In addition, they should know that animals need food to survive while plants need light. They also should understand that animals eat plants or other animals for food, and animals also may use plants (or even other animals) for shelter and nesting.
This prerequisite knowledge will help elementary students expand their knowledge to learn that almost all kinds of animals' food can be traced back to plants and that some source of "energy" is needed for all organisms to stay alive and grow.
Organisms are linked to each other and their environment by the transfer and transformation of matter and energy. The concept of energy transfer brings together insights from the physical and biological sciences. This concept is more difficult for students to understand in biological systems than in physical systems. In physical systems, tracing where energy comes from and goes through is usually directly observable. It is easy to see that fire heats water or that falling water makes electricity. In biological systems, it is difficult to show how energy is stored in a molecular configuration.
The cycling of matter and flow of energy can be found at many biological levels, from the molecular level up to and including the ecosystem level. In the elementary grades, the study of food webs with the transfer of matter can be taught. This entire concept grows slowly over time for students. It is important to note that in the early years, the temptation to simplify matters by saying plants get food from the soil should be resisted.
Ask students if they know the definition of a food chain. Give students time to write their answers down. Then, ask students to share their answers.
Draw on the blackboard a food chain with arrows in between the following (the arrow indicates that “a” is eaten by “b”): plant → snail → bird → fox. Explain to students that this is an example of a food chain. In this example, the plant is eaten by the snail, the snail is eaten by the bird, and the bird is eaten by the fox.
Then, tell them the following information about food chains:
- A food chain shows who’s eating whom.
- There are many food chains.
- Usually a food chain begins with plants, thus they are at the bottom of the food chain.
Next, using your computer and overhead projector, show students Food Chains, on the BBC website. Click “next” in the bottom right corner to go through the three sections. Once you’ve done the section on prey and predators, click on “Activity” in the bottom left corner to do the food chains activity with your students.
Ask students to write the answers to the following questions to solidify what they just learned so that they can build upon this knowledge in the next section:
- Why are green plants called producers? (They make their own food.)
- Why are animals considered consumers? (They get their food from plants or other animals.)
- What is a predator? (An animal that eats other animals.)
- What is a prey? (The animal—"a consumer"—that is being eaten.)
In this part of the lesson, students will explore the food chain in further detail on their own.
First, using the Cycle of Life 1 student esheet, students should go to and watch Food Chain on National Geographic Explorer.
Next, students should start the Chain Reaction activity on the EcoKids website. Have students read the activity instructions at the bottom of the page before doing the activity. This exercise is excellent because it ties together how disruptions in a food chain cause a particular "chain reaction" in the environment.
Once students have watched the movie and gone through the Chain Reaction activity, they should answer the corresponding questions on their Cycle of Life 1 student sheet. Answers to these questions can be found on the Cycle of Life 1 teacher sheet.
Now students can do the Food Chains Quiz from the BBC site. This is a great review of everything that students have learned in this lesson. This quiz is self-explanatory.
Ask students to write one to two paragraphs on the main points of this lesson and what they learned that was the most interesting to them. Have them include (at minimum) the following vocabulary in their writing piece: sun, producer, consumer, decomposer, plants, animals, photosynthesis, food web, and food chain. (The two main points of this lesson are that in food chains almost all kinds of animals’ food can be traced back to plants and that the sun is often the ultimate source of energy needed for all organisms to stay alive and grow.)
Next, have students create/draw their own food chain to turn in for review. Post them somewhere where all students can view and benefit.
Follow this lesson with the second lesson in the Cycle of Life series: Cycle of Life 2: Food Webs.
How a Blue Crab Changes as It Grows is a Science NetLinks lesson that also looks at energy transformations.
Planetpals provides a visual image that encapsulates the entire process of the food chain for any student that may be having difficulty with this subject.