Food Chain Practice

Remember that food chains are used to represent the flow of energy between organisms. As you learned on the last Sci-ber Text page, the arrows in a food chain show the direction of energy flow.

The organisms in a food chain can be producers, consumers, or decomposers.

Producers are green plants capable of making their own food using energy from the sun in a process called photosynthesis.

Consumers are animals that cannot make their own food. They get their energy from other plants and animals. A food chain can have as many as three to four consumers.

There can be many levels of consumers who rely on each other as a food source.

• First level consumers feed directly on plants; an example of this would be a mouse.

• Second level consumers feed on first level consumers; an example of this would be a rattlesnake that eats the mouse.

• Third level consumers feed on second level consumers; an example of this would be a hawk eating the rattlesnake.

• Predators are often second or third level consumers. These organisms obtain their energy by eating a prey. An example of a predator would be a mountain lion.

• Prey then refers to an organism that is eaten by another organism. An example of a prey for a mountain lion is a mule deer.

You can see that because energy is lost at each step of a food chain, it takes a lot of producers to support a few top consumers. The food pyramid below shows an example of this.

Notice that if there were 1000 units of energy at the producers level the primary consumers would receive 100 units of energy, the secondary consumers would receive 10 units of energy, and the tertiary consumer would receive 1 unit of energy. This pyramid helps to demonstrate the loss of energy from one level of the food chain to the next.

• Decomposers are also unable to make their own food. Bacteria and fungi are decomposers. They break down waste products and dead organisms for food. These broken down materials are returned to the soil to be recycled and used by plants again. An example of this would be the mushroom in the picture at the right growing on decaying wood in the forest.

Although decomposers are very important to ecosystems, they are usually not shown on the food chain.

Materials:

• Magazines

• Colored pencils

• Large-sized paper for mounting pictures or drawing

• Scissors

• Glue

Procedure:

You should demonstrate your knowledge of food chains by creating some chains of your own. Draw (or clip pictures from magazines) and color three food chains with at least four organisms in each. Make your food chains for diverse ecosystems ... include food chains from at least one of the following: the desert, the forest, the plains of Africa, the ocean, and the Arctic. Be creative. Be sure to include arrows to show the direction of energy flow. Label each member of the food chain as the producer, first, second, or third level consumer.

Safety concerns: Be sure to follow all sharp safety rules that are specified by your teacher in all general laboratory experiences. Be careful with the scissors that you are not injured. As with all science lab activities, the most important safety rule is to follow all teacher directions.

Assessment:

Look closely at the following list of organisms and drag down to identify each as a producer, consumer, or decomposer.

. Organisms Role in food chain 1 Human 2 Deer 3 Pine tree 4 Mushroom 5 Rabbit 6 Bacteria 7 Mouse 8 Snake 9 Wheat 10 Fly maggot 11 Bluegrass 12 Hawk 13 Millipede 14 Sparrow 15 Cat 16 Frog 17 Algae 18 Trout

Check your answers by highlighting the box below! 1. Consumer, 2. Consumer, 3. Producer, 4. Decomposer, 5. Consumer, 6. Decomposer, 7. Consumer, 8. Consumer, 9. Producer, 10. Decomposer, 11. Producer, 12. Consumer, 13. Consumer, 14. Consumer, 15. Consumer, 16. Consumer, 17. Producer, 18. Consumer

All energy for life on Earth comes from the sun. After the energy leaves the sun it is used by plants on Earth where photosynthesis converts it to sugars. The plants store chemical energy that can be used by the plants, or converted into mechanical energy within an organism (e.g. an animal which eats the plant.) Photosynthesis is the process that explains how energy from the sun is captured by green plants and used to make food. Most of this energy is used to carry on the plant's life activities. The rest of the energy is passed on as food to the next level of the food chain.

The figure at the left shows energy flow in a simple food chain. Notice that at each level of the food chain, about 90% of the energy is lost in the form of heat. The total energy passed from one level to the next is only about one-tenth of the energy received from the previous organism. This means that an animal eating a plant will only get about ten percent of the energy that is stored in the plant. The remainder of the plant's energy is unusable as energy by the animal. Therefore, as you move up the food chain, there is less energy available. Animals located at the top of the food chain need a lot more food to meet their energy needs.

As light energy is transfered between living organisms some energy is used by the organism which obtains the food. Because of the amount of energy that is lost as you move from one level to the next typically, food chains do not usually include more than three to five organisms.

This activity allows you to explain how a food chain can be modeled by indicating the direction of energy flow. Using an arrow to indicate the direction that the energy flows (the arrow points to the organism that gets the energy.)

Below are several food chains. Use the list of organisms provided for each food chain and place these organisms in order according to the flow of energy. Remember to begin with energy coming to Earth. The path should go from the original source to the last organism to use the energy. Each of the items in the list should only be used once on a line.

• Hawk

• Bunny Rabbit

• Sun

• Lettuce

1. ______________
_____________
_____________
______________

• Snake

• Cricket

• Rat

• Seed

• Sun

• Eagle

2. ______
______
______
_______
________
______

• Cod

• Algae

• Sun

• Krill

• Leopard Seal

• Killer Whale

3. _______
________
________
_______
______
_____

• Sun

• Herbivore

• Carnivore

• Producer

• Top Carnivore

4. __________
__________
__________
___________
_________

• Shrubs

• Sun

• Mountain Lion

• Deer

5. ______________
______________
______________
_____________

• Grass

• Cow

• Human

• Sun

6. ______________
______________
______________
______________

• Snake

• Lizard

• Hawk

• Sun

• Grasshopper

• Plant

7. _______
_______
________
_______
_______
_______

Extension:

Take turns comparing what you ate for breakfast, lunch, or dinner with a friend. See if each of you can determine what level of the food chain your food came from!

Assessment:

1. Explain how energy is transferred within an ecosystem.

2. Describe why the sun is the beginning of all food chains.

3. What would happen if the producers in any food chain were destroyed?

What do the arrows represent?

You have learned about food chains and the organisms that are found in them. The reality is that organisms in typically eat more than just one kind of food source. Look closely at the diagram below to get an idea of how mixed up food chains can become. This mixed up combination of food chains is known as a food web.

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