Title of Lesson:  Food Chains and Webs

Length of Lesson:  50 minutes

 Description of the Class:

            Name:  Biology

            Grade Level:  9th

Source of the Lesson:

DiscoverySchool.com, A Demo A Day, ÒFood WebbedÓ lesson, p. 278, ÒTrophic Levels and YOU!Ó

 

TEKS Addressed:

B (3)  A system is a collection of cycles, structures, and processes that interact. Students should understand a whole in terms of its components and how these components relate to each other and to the whole. All systems have basic properties that can be described in terms of space, time, energy, and matter. Change and constancy occur in systems and can be observed and measured as patterns. These patterns help to predict what will happen next and can change over time.

(12)   Science concepts. The student knows that interdependence and interactions occur within an ecosystem. The student is expected to:

(B)  interpret interactions among organisms exhibiting predation, parasitism, commensalism, and mutualism;

(E)  investigate and explain the interactions in an ecosystem including food chains, food webs, and food pyramids

I.      Overview

This lesson is intended to emphasize the complexity of food webs and distinguish them from simple food chains.  A video will be used to allow students to see interactions among different trophic levels and analyze them.

 

II.                Performance Objectives

The student will be able to:

-list the three primary trophic levels, producer, consumer and decomposer and             apply to marine environments

-compare chemosynthesis to photosynthesis

-distinguish between a food chain and a food web

-define biomagnification

 

 

III.      Resources, Materials, and Supplies Needed

1 package of index cards,  3 different colored balls of yarn, Cut-out drawings of the following marine organisms for a class of 30 students:

16 phytoplankton (diatoms)                               40 green "energy" circles

8 zooplankton (copepods)                                  8 red "energy" circles (toxin)

4 herring

2 chum salmon                                                     chart paper or chalkboard

 

IV.              Safety Considerations

Students will be instructed to throw the balls carefully;  any student with obvious intention of harming another student will be immediately removed from the activity.

Five E Organization 

                        Teacher Does                                                            Student Does

 

Engage:

Learning Experience

  Students will make their own food ÒwebÓ using yarn attached to balls.  As they enter the room, each desk will have an index card on it with a different organism marked on the back of the card.  Students will be told to stand in a circle.  The first ball, the ÒsunÓ will be thrown to one of the students who could use the sunÕs energy;  the ball will then be passed from the plant to an animal that could use the plant.  This will get repeated with two more balls until all students are included in a complex web with different trophic levels.  If anyone is left out, they will be asked how they can be included.

Questions:  Who can use the sunlight to harvest energy?  What is this process called?  Who can use the plants? Where does an animal like a zebra fit in?  Are they always consumers? What does this look like?  How is it different from a food chain?  Where would bacteria fit into this scheme?

 

 

 

Hoped for student response:  Hoped for student response:  Students participate in the activity with no behavioral problems.  All students become incorporated into the food web.  Students are engaged in the activity

 

 

 

            Expected student responses:  Plants use the sun in photosynthesis.  All animals can use plants in one way or another.  Zebras eat plants, and animals like lions eat the zebra.  This looks like a web.  A chain is a more direct relationship from one animal to the next, like from sun to plant to animal;  there is no interconnection.  Bacteria might be decomposers?

 

Evaluate:  Students should be able to identify the three main trophic levels.  They should also question whether there are more than three levels and engage in discovering how all animals interact.

 

 Explore:

Learning Experience(s):

1.     1.      Introduce the concept of a marine food chain with primary producers (phytoplankton); primary consumers (zooplankton); secondary consumers (herring and salmon); and tertiary consumers (killer whales). Have students come to the board and draw this simple food chain on the board with arrows to show energy transfer.

2.     2.    Have students pull a drawing of a marine organism out of a paper bag. (Teacher is a killer whale). Hand out all 48 energy circles to the diatoms (each diatom will receive three energy circles), and randomly hand out the red circles.

3.     3.      Demonstrate the food chain by having the copepods "eat" the diatoms by tagging. When a diatom is tagged by a copepod, it must give up one energy circle. Wait approximately three minutes and release the herring. The herring get two energy circles when they tag a copepod. Salmon get four energy circles per tag, and the killer whale gets eight. At the end of the game, record the numbers of energy circles accumulated for each feeding group on a chart, (with the diatoms charted at the base of what will become a pyramid). Have students observe the amount of energy circles required by each higher level of feeder. Now explain that the true amount is actually 10 rather than 2 times these amounts required. Let them consider the mathematical effect of this.

4.     Now explain that a toxin that has and entered the enviormententhas entered the ocean from a passing ship. The phytoplankton that convert inorganic materials into organic matter also picked up a small amount of toxin and this is now

 

Questions:  

 

 

Hoped for student response:

 

4.         Students will use the materials provided to role play the levels within a trophic system.

   

 

 

 

 

Expected Student Response:

In the marine environment, phytoplankton are the producers while killer whale are predators.  Other organisms fall in between.  Phytoplankton are small invertebrate organisms that photosynthesize.  They are very important globally because they are very numerous and convert a lot of CO2.   It takes more energy to feed higher energy level feeders than lower level feeders.  If it takes a lot of energy to feed animals, then if we just eat grains more people could get the energy more efficiently.

 

 

 

 

 

 

 

 

 

 

 

 

stored in the tissue of some of the diatoms. Record the level of toxin per individual at each feeding level. End with the killer whale and follow the activity with a discussion of the effects of pollution and biomagnification.

Questions:

In a marine environment, who are the consumers and producers? What are phytoplankton?  Why do higher level feeders need more energy circles?  How could you relate this to world hunger?  Could you come up with a feasible solution? What happened when there was a toxin in the environment?  Who felt it the most?  This is called biomagnification;  as a substance that canÕt be metabolized passes through the trophic levels, it accumulates in greater amounts through increased trophic levels.

 Evaluate:  Students should be up and participating in the activity.  They should be interacting with each other and cooperating.

 

Explain:

Learning Experience(s):  Students will become more familiar with the vocabulary associated with food chains and food webs.

 

 

            Questions:  What is a food chain?  What is the order in the food chain?  Why is it less complex than a food web?  What would happen if, all of a sudden, plants couldnÕt harness the sunÕs energy for photosynthesis anymore? Are there other ways to start a food chain than with photosynthesis? (introduce chemosynthesis and its equation)  What is different between chemosynthesis and photosynthesis?  What is similar?

 

 

Hoped for student response:  Students contribute to the conversation and take note of vocabulary they are not familiar with.

 

 

            Expected student responses:  A food chain is the passage from on level to the next.  Food passes from producers to primary consumers, to secondary consumers, and is then broken down by decomposers.  Food webs are a better representation because in real communities, there are interrelated food chain interactions that become woven into a web.  Energy can flow in many directions.  If plants couldnÕt do photosynthesis, life on earth would stop.  Chemosynthesis doesnÕt require light to occur and uses H2S, whereas photosynthesis uses light.  Both use C02 and H20 to occur, and both produce C6H12O6.

 

Evaluate:  Students should be participating in class discussion.

 

Extend/Elaborate:

Learning Experience(s):  Students will be taken on a field trip to observe food chains at work.  They will record their observations in a journal and turn it in.

 Questions to think about while on the trip:  What toxins might be present in this area?

 

Hoped for student response:  Students research possible insects, plants and small animals that might be present in the Austin area.

 Evaluate:  Points will be given as participation grades.  As long as a student is active in the activity, they will be awarded full credit for the day.