Biomagnification Lab
Goal: The purpose of this lab is to demonstrate the concept of biomagnification, and to show how persistent pollutants increase in concentration as the travel up the food chain.
A Few Reminders:
Measuring the Volume of Liquids-
When measuring the volume of liquids in graduated cylinders, we use the bottom of the meiscus (that concave line the water makes at the top) as the point from which we measure.
Calculating Concentrations-
The percent concentration of one substance in a mixture of two or more substances is equal to the volume of that substance divided by the total volume of the mixture times one hundrede.
Example: 1 ml of chocolate syrup mixed with 9 ml of milk makes 10 ml of chocolate milk.
The concentration of chocolate syrup in the chocolate milk is 1/10*100 or 10%.
In front of you, you will find the following items.
1 Beaker of water
2 1000 ml graduated cylinders
2 100 ml graduated cylinders
3 10 ml graduated cylinders
1 Stir rod
1 Cup of oil
1 Cup of colored water
Procedure: Modeling the Ecological Pyramid
1.Please decant 990 ml of water into one of the 1000 ml graduated cylinders. This graduated cylinder represents the first trophic level, the primary producers, in our food chain.
2. Please measure 10 ml of colored water using one of the 10 ml graduated cylinders.
3. Please pour the 10 ml of colored water into the graduated cylinder with 990 ml of water.
What is the concentration of colored water in this new mixture?
4. Now, please measure out 100 ml of this newly colored water from the 1000 ml graduated cylinder into the 100 ml graduated cylinder. This 100 ml graduated cylinder represents the second trophic level, the primary consumers, in our food chain.
Why does 1000ml of primary producers only constitute 100ml of primary consumers?
What is the concentration of colored water in the 100 ml graduated cylinder?
5. Finally, please measure out 10 ml of colored water from the 100 ml graduated cylinder into the 10 ml graduated cylinder. This 10 ml graduated cylinder represents the third trophic level, the secondary consumers, in our food chain.
What is the concentration of colored water in the 10 ml graduated cylinder?
What percentage of the first trophic level made it to the third trophic level?
Procedure: Modeling Biomagnification
1.Please use the other set of graduated cylinders for this part of the lab.
2. Please decant 990 ml of water into the 1000ml graduated cylinder. This graduated cylinder represents the first trophic level, the primary producers, in our food chain.
3. Measure 10 ml of oil into one of the 10 ml graduated cylinders and then add this oil to the 990 ml of water in the 1000ml graduated cylinder.
4. Set the dirty 10 ml graduated cylinder aside and make sure not to use it for the rest of the lab.
5. Let the oil sit until all of the droplets have coalesced into one film at the top of the graduated cylinder. The oil represents a POP, a persistent organic pollutant. Its insolubility with water represents its resistance to biological degradation and metabolism.
6. Record the volume of water and the volume of oil in the 1000 ml graduated cylinder in the table below, and calculate the % concentration of oil.
What is the % concentration of oil in the first trophic level of our food chain?
7. Carefully, pour 100 ml of the oil/water mixture from the 1000 ml graduated cylinder into the 100 ml graduated cylinder. Note: Accurately pouring this mixture of oil and water can be difficult, so pour slowly.
8. Let the mixture settle so that all of the oil droplets have coalesced into one layer at the top of the cylinder. You may use the stir rod to help the oil droplets to coalesce
9. Record the volume of water and the volume of oil in the 100 ml graduated cylinder in the table below, and calculate the % concentration of oil.
What is the % concentration of oil in the second trophic level of our food chain?
10. Carefully, pour 10 ml of the oil/water mixture from the 100 ml graduated cylinder into the 10 ml graduated cylinder, using the same cautions as before.
11. Record the volume of water and the volume of oil in the 10 ml graduated cylinder in the table below, and calculate the % concentration of oil.
What is the % concentration of oil in the third trophic level of our food chain?
Trophic Leve / Graduated Cylinder / Volume of Water / Volume of Oil / Total Volume of Mixture / % oilFirst / 1000 ml / 1000 ml
Second / 100 ml / 100 ml
Third / 10 ml / 10 ml
Summary Questions:
How did the % concentration of oil change from one trophic level to the next?
How is this change in % concentration similar to the biomagnification of a peristant organic pollutant in a food chain?
Imagine for a moment that the first trophic level represents the phytoplankton population of Puget Sound, the second trophic level represents the euphausiids and the third trophic level is salmon. Please pour 1 ml of water into an extra dixie cup, which represents the fourth trophic level, the orcas.
Qualitatively, how would you describe this sample and how does it explain the extremely high levels of POPs found in Puget Sound Orcas?