Investigation 1 – Lab
This Investigation is designed to:
- illustrate to you that energy flow through an ecosystem is unidirectional and inefficient,
- illustrate to you that the energy content of an ecosystem is directly related to the amount of biomass in the ecosystem, and
- guide you to conclude that the amount of energy that initially enters the ecosystem through photosynthesis determines the amount of energy available for biomass accumulation.
Student Preparation for the Investigation includes gathering the following materials.
Note: The materials are listed in your SDR. They are also listed below for your reference.
- (1) test tube rack
- (7) plastic droppers
- (1) empty 400 ml beaker
- (1) 100 ml beaker of sand
- (1) liter pitcher of split peas
- (1) paper lunch bag
- (27) small bears
- (7) medium bears
- (3) large bears
- (1) weigh dish
- (1) triple beam balance
Direct one student from each lab group to collect the materials listed in their SDRs.
- You will first use a model to demonstrate how energy flows through an ecosystem.
- Reflect on the PreLab video as you move through the procedural steps.
- During the Experiment, every procedural step is important. If one step is skipped, data can become invalid. To help you keep on track, read each step thoroughly, complete the step, then check it off (Read it – Do it – Check it).
- Complete all of the procedural steps in your SDR.
The Experiment includes the following:
- Label the six test tubes “Blank”, “Sun”, “Plants”, “Herbivores”, “Carnivores”, and “Detritivores”.
- Label the empty 400 ml beaker “Waste”.
- Use the graduated cylinder to fill the labeled test tubes as follows:
A. Fill the “Blank” test tube with 20 ml of water.
B. Fill the “Sun” test tube with 20 ml of “Sun Stock Solution”.
C. Fill the “Plants” test tube with 20 ml of “Plants Stock Solution”.
D. Fill the “Herbivores” test tube with 20 ml of “Herbivores Stock Solution”.
E. Fill the “Carnivores” test tube with 20 ml of “Carnivores Stock Solution”.
F. Fill the “Detritivores” test tube with 20 ml of “Detritivores Stock Solution”.
- Find the energy in the levels of the ecosystem by measuring the absorbance for the samples below.
A. Set the wavelength to 630 nm.
B. Fill the cuvette with the sample using a plastic dropper. Use a new plastic dropper for each sample. (Remember to zero the spectrophotometer using a “blank” before you begin collecting data.)
C. Place the cuvette in the sample compartment and close the lid.
D. Record the absorbance for each sample in Table A. Remember the absorbance represents the amount of energy at each level of the ecosystem.
E. Pour the sample back into the test tube.
F. Rinse the cuvette with water from the water bottle. Pour the rinse water into the “Waste” beaker.
- Determine the effect of the presence of extra dust or clouds in the atmosphere on the amount of energy that reaches the Earth.
A. Transfer the amount of energy from the “Sun” solution in Table A to Table B.
B. Use the spectrophotometer to find the amount of energy in the “Cloudy Sky” solution. Refer to the Procedure Spectrophotometer Use and Operation if you need help.
C. Record your results in Table B.
- Before beginning Trial 2, if you need help, refer to the Procedures, Triple Beam Balance Equilibration, Triple Beam Balance Use and Operation, and Measuring Mass Using a Weigh Dish or Beaker.
- Determine the mass of the biomass in each level of the land ecosystem. Do this by using a model of the ecosystem.
A. Locate the containers of split peas, small bears, medium bears, and large bears. These items will represent the levels in an ecosystem.
B. Label the containers as follows: • split pea container —-“Producers” • the container small bears—–“Herbivores” • the container of medium bears —-“Carnivores” • the sand —–“Detritivores”
C. Use the triple beam balance to determine the mass of the biomass at each level of the ecosystem. Use the paper bag as a container when massing the “Producers”.
D. Record the mass of the biomass in each level of the ecosystem in Table C.
- Determine how adding omnivores affects the biomass of the ecosystem.
A. Transfer the masses of the biomass of the “Plants” and “Detritivores” from the first model to table D.
B. Label the container of large bears “Omnivores.”
C. Remove 3 bears from the “Herbivores” container.
D. Remove 3 bears from the “Carnivores” container.
E. Determine the masses of the biomass of the “Herbivores,” “Carnivores,” and “Omnivores.” Record masses of the biomass in each level in table D.
Be sure to clean up your lab bench after the experiment.