Title:

Food Chains and Webs        

Grade:  Upper Elementary (4)

Time:   45 minutes 

Objectives: Students will…

• Describe “food chain”
• Define the roles in a food chain (producer, primary consumer, secondary consumer)
• Give an example of a food chain
• Explain the difference between a food chain and food web

Materials:

• Chalkboard or whiteboard
• Open space for activities
• Pasta or peanuts
• Animal and plant name tags
• Ball of yarn or twine

Introduction

Ask students what they had for lunch (or breakfast) that day.  If there was meat in the meal, ask what that animal ate.  When you eat, you become part of a food chain. 

Procedure:

1. Food Chains

Ask students if they know what a food chain is.  If not, walk them through making one (What eats grass?  What eats the rabbit?  What might eat the fox?)  Draw this on the whiteboard or chalkboard.   

The sun is at the beginning of each food chain, because it supplies the energy that will travel through the plants and animals.  The next step in any food chain is a plant, whether it is algae, phytoplankton, or a “regular” plant.  Plants are special because they actually create their own food, using the heat energy from the sun.  There are tiny holes in the leaves of a plant that let water (H₂O) and carbon dioxide (CO₂) in, and let oxygen (O₂) out.   

A plant uses CO₂ and H₂O, plus the heat energy of the sun to make sugar.  It essentially takes the atoms from the CO₂ and H₂O and rearranges them into sugar (C₆H₁₂O₄) and oxygen gas (O₂). 

Because the plant uses sun energy to produce food energy, it is called a producer.  Ask students if they know a word to describe an animal that eats only plants (herbivore, vegetarian).  In a food chain, an animal that eats (or consumes) a producer is called a first, or primary, consumer. An animal that eats a first consumer (called a carnivore or predator) is called a second (secondary) consumer, and so on up the line.   
 

An example of a food chain:

\

      Sun  Producer  1^st Consumer  2^nd Consumer 
 

2. Energy in the Food Chain

The students will now model how energy passes up through the food chain.  Do they think that a lot of energy will pass on through each level, or only a little will pass on?  Ask them to explain why they chose as they did. 

Divide students into groups of 3 or 4. If you can do this part outside with more room, even better.  Have each group line up, and then spread out so that their outstretched arms do not touch.  Give the person at the start of each line a large double handful of pasta pieces or peanuts.  Have them count how many they are holding.  Record each group’s starting number on a chart on the board.  The person holding the pasta is a plant, at the beginning of the food chain.  If they are a plant, what is the next person in the line?  The first consumer. The next person?  The second consumer, and so on. 

Explain the rules of the game:

• Each piece of pasta equals 1 unit of energy
• The goal is to pass the energy on to the next part of the food chain
• The pasta must be passed on in one chunk – the only things they can toss or catch with are their hands. 
• As each new level gets the energy, they need to count how many they caught so it can be recorded.  Only pieces in hand count.

Have students begin the game, pausing at each level to record numbers.  A sample chart: 

            Plant  1^st consumer  2^nd consumer  3^rd consumer

Group 1 58       5        2    1 

Group 2 47       4        1    0 

Group 3 

Group 4 
 

After students have cleaned up, have them look at the numbers.  Were their predictions correct?  In general, only 1/10 of energy passes to the next level.  If a plant has 10 units of energy, how much would the rabbit get?  1 unit.  How much would the coyote get?  1/10 of a unit.  How much would a mountain lion get if it ate the coyote?  1/100 of a unit.   

Where does all the extra energy go?  Breathing, moving, hunting, growing, etc.  Which uses and needs more energy, an herbivore or a carnivore? 

3. Food Webs

Ask students if animals always eat the same thing.  No, they will eat a variety of foods because relying on only one is very dangerous – if your food has a bad year, so do you.  Have students stand in a large circle.  Pass out one name tag to each student.  Ask them to silently look around the group and think of one way their animal would use or be used by each other member of the circle.  This can be as food, shelter, etc. 

Show students the ball of yarn.  Starting with yourself as a demonstration, run through the basics of the activity.  Hold the ball of yarn, holding the end of the string in one hand.  Look for someone in the circle that you (as the plant or animal on the nametag) would use or be used by.  Say their name, and then toss the ball of string, holding onto the end.  The next person will hold onto their part of the string, then pass the ball to someone they would use or be used by.  They should pass it to someone that is not yet holding the string.  Continue until everyone is holding the string.   

What shape is the string in?  It looks like a spider web.  A food web is a group of animals and plants that are related to each other, even though it may not be directly.   

4. Hidden connections

What would happen if one part of the web was removed?  Have students pull gently back on the string until it is taut.  Starting with yourself again, drop your part of the string.  Instruct students that if their string now feels loose, to drop their hold on the string, and continue going until all have dropped the string.  Often, removing part of a food web can have unforeseen consequences.  A real life example:  There used to be many sea otters off the California coast.  Sea otters love to eat sea urchins.  When otters were killed for their fur, the numbers started dropping quickly.  With few otters, the sea urchins boomed in number.  Sea urchins eat algae, including the giant kelp that make up kelp forests in the Pacific.  The sea urchins soon removed too much kelp, and some fish didn’t have a habitat.  By removing sea otters from the food web, a fish had no place to live. 

Conclusion

Have students give you examples of food webs, and discuss which roles each organism plays.  Can the same animal play different roles in different food chains?  Sure, a human could be a first consumer in one food chain (eating lettuce), or a second consumer in another (by eating a hamburger).

Eastern Forest Food Web Interactions      

Organism  Food     Predators

Black bear  fruit, nuts, plants, small animals,  humans, mountain lions,

      white-tailed deer    other bears 


Red maple  many animals live in it  rabbits, dear, bear, bees, birds  


Honeybee  pollen and nectar from flowers birds, bears, raccoons 


Great horned owl small animals, birds, even a fox other great horned owls,    squirrels    Nests in trees 


Raccoon  fruit, berries, seeds, plants  mountain lions, bears,     Insects, eggs, small mammals  humans 


Sphinx moth   as caterpillar, eats grape leaves, screech owl, raccoon,

                  As adult, nectar

                   

Deer mouse  seeds, nuts, fruit, berries  screech owl, great horned owl,      fox, mountain lion

                  

Spotted wintergreen      deer, mice, rabbits 


Red fox  small animals, fruit, seeds, insects mountain lion, great          horned owl, bear, humans 


Ladybug beetle aphids     birds, raccoons,  


Northern cardinal seeds, berries    screech owl great horned owl,        fox 


Wild turkey  nuts, seeds, berries, insects  mountain lion, raccoon will    Roost in trees at night   eat eggs  


Song sparrow  seeds, berries, insects   raccoons, foxes, owls

                  builds nests in trees 


High bush blueberry      deer, bear, foxes, turkeys,

      cardinals, sparrows, fox, squirrels 


Screech owl  insects, small animals, birds  great horned owls, foxes    Nests in tree holes   mountain lions  
 


Food Web Interactions        

White oak  many animals live in it  squirrels, deer, turkey, bear,         raccoon,  


Flying squirrel  nuts, seeds, berries   fox, mountain lion, bear, humans,

                  Nests in trees    great horned owl 


American beech many animals live in it  squirrels, birds, turkey, raccoon,

      fox, bear, deer 


White-tailed deer nuts, fruit, berries, plants  mountain lion, bear, humans 


Mountain lion  meat, berries    bear, humans