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# Investigation 2 – PostLab

### ANALYZE IT

Complete the Analysis Questions in your SDR then discuss them as a class.

• Create a line graph (using a best fit line) that shows the amount of oxygen used by the “Live Herbivore” over time. Remember to start the graph by plotting the amount of oxygen that was in the beaker before the “Live Herbivore” was added. Use the data from Tables A and B to create your graph.

• Create a line graph (using a best fit line) that shows the amount of oxygen used by the “Dead Herbivore”. Remember to start the graph by plotting the amount of oxygen that was in the beaker before the “Dead Herbivore” was added. Use the data from Tables C and D to create your graph.

Note: you may have observed that the oxygen level initially decreases slightly when the dead yeast is added to the beaker. Therefore, you might have inferred that this decrease is due to oxygen consumption by the yeast. However, the initial decrease in oxygen level is likely due to the increase in the volume of the solution, which dilutes the oxygen concentration.

• Look at your graph of the “Live Herbivore”. What happened to the oxygen level over time?
• Remember, the more oxygen that is used up, the more energy that an animal uses to live. Did the “Live Herbivore” use energy to live? Explain your answer.
• Look at your graph of the “Dead Herbivore”. What happened to the oxygen level over time?
• The more oxygen that is used up, the more energy that an animal uses to live. Did the “Dead Herbivore” use energy to live? Explain your answer.
• Describe the difference in the amount of oxygen that was used by the “Live Herbivore” and the “Dead Herbivore.”

• In your models, sugar represented food, yeast represented an herbivore, and dissolved oxygen represented the energy consumed by the herbivore. Based on your results, was the live herbivore able to store all the energy it consumed? Use your data to explain your answer.
• How does the data from the “Dead Herbivore” model show that cellular respiration is the reason for the decrease in the amount of energy available for transfer from the herbivores to the next level of the ecosystem?
• In theory, all of the energy that is consumed at one level should be available to the next level. Thus, energy transfer should be 100% efficient. How do the results of your experiment demonstrate why energy transfer between the levels of an ecosystem is inefficient?

### GET FOCUSED

Complete the Focus Question in your SDR then discuss it as a class.

• What affects the efficiency of energy transfer within an ecosystem? The efficiency of energy transfer is affected by the use of energy by an organism. All organisms must use some energy to live, and therefore cannot store all the energy that they consume. Therefore, the transfer of energy from one level to another is not 100% efficient. This was demonstrated by the “Live Herbivore” model. The “Live Herbivore” consumed oxygen, indicating that it was using energy to live. The energy used by the herbivore to live was no longer available to any organism that might consume the herbivore.

Tool: Conclusions

At the beginning of the Investigation, you used the Prediction tool to think of the possible answers to the following questions. Now, use the Conclusions tool to answer the following questions based on your results from this Investigation.

• How is the energy in an ecosystem related to its biomass?
• Is all of the energy that is consumed by an animal in an ecosystem available to the next animal in the food chain of the ecosystem?