Each student of group should have a copy of the FOOD WEB, and some of the blank ENERGY PYRAMIDS/MERCURY LADDER or they can use DAY 2 WORKSHEET.
You can also print out as an overhead, use a projector, have the students view on line or hand out the sample BIOMAGNIFICATION DIAGRAM.
There are some optional activities depending on the time, space,previous knowledge of students, curriculum, etc.:
For Energy Transfer per group:
This activity requires an outdoor space that can get wet.
Signs (index cards or larger) and string to hang signs on each student
Two five gallon buckets (or other large containers for water)
Large cups(20 oz size)--at least one per student
Graduated cylinder or other measuring device to measure final water volume.
For Project Flow--Lesson 2:Who's Eating Whom? :
A relatively large, open room, or outdoor space
construction paper: red, blue, brown and green to make tokens
Copy of feeding behavior cards (provided with lesson)
For Deadly Links (see DAY 2 TEACHER RESOURCE DEADLY LINKS sheet)
1 pound each of plain and colored pasta/ 20 students.
signs and string to hang signs around students' necks
1 paper lunch bag/student
Teacher Presentation & Motivation:
Review the MERCURY DIAGRAM from the end of the lesson on the first and ask if anyone figured out how so little mercury could become so much. Show the students the bottom of the diagram (2nd page if using hard copy) with the food chain. Alternatively, use the Drill Day 2 from the DAY1 POWERPOINT PRESENTATION as an introduction.
Review the concept of a food chain or web, or introduce it if it has not been previously taught. There are resources listed to help teach food chains and energy transfers. Directions for the Deadly Links game are given in DAY 2 TEACHER RESOURCE DEADLY LINKS GAME sheet.There are two other active games for teaching energy transfer from the internet cited . Energy transfer is a confusing concept, so it is a good idea to do one of the activities if you have the time and resources. They are also fun!
Whether or not a game is played, energy calculations should be done. The food web diagram provided is based on the feeding cards provided with the Project Flow lesson. Even if the activity isn't used, the information is useful for making food chains to do the energy calculations.
Once the students understand the transfer of energy, return to the concept of mercury. How come mercury accumulates if energy is lost? See if the students can come up with the answer from the web sites they visited yesterday, or reading the side of the introductory food chain they saw today. The important fact to know is that mercury, unlike energy, is stored for a long period of time in the fat cells of the body and so it accumulates. In addition, because energy is lost at each level, the higher you climb on the food chain/energy pyramid, the more organisms in total you are consuming, and therefore the more mercury you are consuming.
The numbers used in these activities were chosen for simplicity. The loss of energy at each level of the food chain is estimated to be 90% for the purposes of this activity. Slightly more accurate numbers are 17% of energy is transferred from producers to consumers, and 4.5% is transferred from primary consumer to secondary consumer (these can be rounded to 20% and 5%) In any case it is all an estimate and the numbers are important in that they illustrate the concept. The activity can assume more mathematical sophistication depending on the level of the students and/or if done in conjunction with a math class. Some math extensions in conjunction with the Deadly Links game are explained on MATH FOLLOW UP sheet. In depth analysis of the data from the games or of the movement of toxins up the food chain are essential to students' understanding of bioaccumulation
Activity 1 - Food Chains
Basic knowledge of food chains and food webs is assumed in the remainder of the lesson. If you are teaching this material at this point, below are two resources which have good explanations.
The Food Chain Page is an excellent resource. It not only contains the basics of food chains and food webs, but information about the transfer of energy and biomass in living systems, in some detail.
Food Chains and Webs is also a good source of background and general information. It also contains a link to some good information about bioaccumulation and biomagnification.
Introduce or review the concept of an energy pyramid and the loss of energy at each level of a food chain. Use WORKSHEET DAY 2 to review food chains and introduce the Deadly Links game.
Alternatively, begin with a simple food chain. One example is:
Algae ------>Insect------> Crayfish--------> Heron
Make sure that students know that algae is the plant and so is the producer, the insect is the primary (first order) consumer that eats plants, the crayfish is the secondary (second order) consumer that eats plant eaters, and the heron the tertiary (third order) consumer that eats animals that eat other animals.
Explain that only 10% (or whichever number you choose to use) of the energy in an organism is conserved as you go up the food chain, so in order to gain enough energy ( assume all organisms need a random number (1000, or 10000 are convenient) units of energy to survive for a time period) the heron has to eat many crayfish and so there must be a number of crayfish eating quite a few insects and many insects eating many plants. Show the energy pyramid.
Have the students answer the following questions as a class.
1. According to the pyramid, what is the ratio of the energy available to the tertiary consumer to the energy available from the producers? (1/1000)
2. If 100 insects eat 1000 algae plants, how many crayfish can they provide with energy? (10)
3. What happens to the pyramid if there are 10 insects eating 100 algae plants? (there is only one crayfish, and so not enough energy for the heron)
4. If there are 5000 insects how many algae plants are necessary to provide them with energy? (50,000) How many crayfish can they support? (500) How many herons can those crayfish support? (50)
(adapted from: It's all Interconnected)
You can have students make up more questions, or you can make up more questions as needed.
If you are planning to play the Deadly Links game or either of the other games this is the appropriate time to do it.
Show the students or hand out the FOOD WEB and give each student the ENERGY PYRAMID-MERCURY LADDER worksheet. As a class find food chains within the food web. Note that the food chains can be different lengths.
Have each student or group choose a food chain and fill in the energy pyramid beginning at the top with one of that organism at the highest level.(see EXAMPLE of ENERGY PYRAMID /MERCURY LADDER) Not all levels will be necessarily be filled in?the more levels there are, the more producers will be necessary to support that pyramid.. Review the numbers in the pyramid with the class. Remind the students that these numbers are examples!!!
See MATH FOLLOW UP sheet for ideas to use in math class in conjunction with the Deadly Links game.
Activity 2 - Bioaccumulation and BioMagnification
Using the same food chain they used in activity one, have students imagine that mercury has entered the water. This is a good opportunity to review the first part of the lesson and ask what are the possible ways that mercury can enter the water supply. Let students look at their organizers if necessary.
Mercury is now in the water in concentrations of 1ppt. Review what a ppt is and have students give you some examples.
Have the students imagine the plants in the water are exposed to this mercury. (For an example, imagine that this concentration of mercury is introduced each time it rains…)
The plants take in the mercury with the water they use, and it is stored in their tissues, primarily in fat tissue. Very little is released once it is in the tissue and so the plant can accumulate quite a large amount of mercury—this is called BIOACCUMULATION.
(see "Bioaccumulation and Biomagnification" for more information)
At the bottom of the mercury ladder, have the students write plants. Estimate that the plants have accumulated 250 ppt of mercury. Have the students fill in the ladder with the amounts of mercury assuming each organism needs a set amount of energy (like the previous activity, 1000 or 10,000 units are easy numbers to use)It should become apparent that the higher up on the food chain you are, the more mercury you accumulate.
The same organism may contain different amounts of mercury if they are on different levels of two different food chains. This is why the estimates of mercury in any one organism is an average of possibilities and an estimate.
Show the BIOMAGNIFICATION DIAGRAM. Point out to students that the predicted numbers for total PCB (another pollutant stored in fats) accumulation in a tertiary consumer in the Great Lakes are predicted to be about 10x the numbers arrived at in our exercise.
This phenomenon of increasing concentration as you proceed up the food chain is called BIOMAGNIFICATION.
Review with students the difference between how energy and how mercury travel up a food chain. What makes mercury and other similar toxins so dangerous is that they accumulate and then magnify as they go up the rungs of the food chain.
Tell students that the next activity involves seeing the connection between the food chains they have just studied and the mercury menus in the previous lesson. If there is time, see if they can make the connection.