Food Webs

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SWBAT compare food chains to food webs and explain the differences.

Big Idea

Students explain the effect of pollution entering the food web.


5 minutes

Teacher Tip: This lesson is intended to demonstrate the inter-connectivity of various food chains within a biome. Through an interactive activity, students see the connections made between the organisms and from a short video clip on mercury in fish, they identify how pollution can affect a biome through the food web, addressing MS-LS2-4. For this lesson, you need a device with an internet connection and projection capabilities for the video clip.  You also need to print and cut out the organisms for the EXPLORE activity and a spool of yarn or string. 

To begin the lesson, students reflect on the prior lesson, Food Chains, by answering the following prompt in their notes sheets individually: 



Where does the energy start in a food chain? (the sun)


15 minutes

For this activity, you need to pre-cut the images and pass out one per student, ensuring someone has the sun and a nice mix of producers, herbivores, omnivores, carnivores, decomposers etc. This really depends on the number of students you have in your class. Once all students have an image, ask them to stand.  

Ask: Where does the energy start in a food chain? (sun)

Throw the yarn to the sun and let the student know to NOT let go of the string.  

Ask: Who uses the sun to make their own food? (producers)

Sun throws yarn to the various producers. 

Ask: Who consumers the producers? (herbivores)

Last producer throws yarn to the various herbivores and omnivores who eat plants. This continues until you reach the last decomposer.

Once all students have a section of yarn, ask: What happens if there is a new insect that comes along and destroys all of the producers?

All of the producers let go of the string. 

Ask: What happens to those of you who eat the producers? 

Continue until all of the organisms have let go of the string, except for the sun. 


After the activity, students answer the following questions in their notes sheet: 

  • What does a food web show?
  • What happens when one organism within the food web dies out or becomes sick?


5 minutes

Next, students will watch a quick video clip demonstrating how mercury can enter the food web and affect the habitat.  Students will address the following prompt while viewing the clip: 

EXPLAIN: Watch the CBS News report on mercury poisoning within the ocean habitat. Address the prompts below.

What is poisoning the fish?

How does the mercury get into the oceans?

What does the ocean food chain look like?

Food Web


5 minutes

Students now contemplate what happens when pollution enters the food web. What effects does it have on the organisms and on the food chains? 

ELABORATE: Discuss how pollution can destroy a habitat through its organisms.

If the smallest fish have poison in their bodies, explain what happens when something bigger eats them.

Sample answers should include mention of pollution entering the food chain and upsetting the balance within the food web and ecosystem, see ELABORATE student sample.


5 minutes

As an exit ticket type activity, students individually answer the following question on their notes sheet: 

EVALUATE: How are food webs and food chains connected?


I am expecting to see that students understand that a food web is a compilation of all of the food chains within an ecosystem.  They should explain the interconnection of the two concepts.