2024 AP Environmental Science Free-Response Questions

ENVIRONMENTAL SCIENCE SECTION II Time—1 hour and 10 minutes 3 Questions Directions: Answer all three questions, which are weighted equally; the suggested time is about 22 minutes for answering each question. Write all your answers in the Free Response booklet. Where calculations are required, clearly show how you arrived at your answer. Where explanation or discussion is required, support your answers with relevant information and/or specific examples. You may plan your answers in this orange booklet, but no credit will be given for anything written in this booklet. You will only earn credit for what you write in the separate Free Response booklet. 1. Researchers are studying the stream ecosystem shown in the following diagram. They have identified five different zones based on the dissolved oxygen levels and biological oxygen demand as the water flows downstream. Biological oxygen demand is the amount of oxygen needed by bacteria and other microorganisms to break down organic material in water. Some of the most common fish and macroinvertebrate species found in each zone are listed in the diagram. Dissolved Oxygen and Biological Oxygen Demand in a Stream Ecosystem Zone A: adult fish; mayfly, stone fly, and caddis fly larvae Zone B: blackfly and midge larvae Zone C: sludge worms; midge and mosquito larvae Zone D: adult fish; blackfly and midge larvae Zone E: adult fish; mayfly, stone fly, and caddis fly larvae Y-axis: High to Low X-axis: Direction of Streamflow Legend: — Dissolved oxygen - - - Biological oxygen demand (a) Based on the information in the diagram, identify the zone with the lowest level of dissolved oxygen. (b) Based on the information in the diagram, describe the relationship between biological oxygen demand and dissolved oxygen. (c) Based on the information in the diagram, identify the zone where there is most likely point-source water pollution discharged into the stream. The research team is interested in investigating the relationship between dissolved oxygen levels and macroinvertebrate species richness in the stream. Researchers counted the number of macroinvertebrate species in zones A, B, and C during the summer months. The researchers selected zone A to serve as the control in the investigation. (d) Identify the dependent variable in the researchers' investigation. (e) Identify a testable hypothesis for the researchers' investigation. (f) Describe the reason the researchers selected zone A to serve as the control in the investigation. The researchers decided to repeat their data collection during the winter months. (g) Explain how the modification to collect data in the winter months could alter the results of the investigation. Stream ecosystems are affected by point-source organic pollution in a variety of ways. (h) Describe the effect that the introduction of raw sewage into the stream could have on the population of bacteria in the stream. (i) Identify an abiotic factor other than dissolved oxygen and organic pollution that could also influence the population size of bacteria in the stream. (j) Explain how persistent organic pollutants can affect higher trophic levels in an aquatic food web. Begin your response to this question at the top of a new page in the separate Free Response booklet and fill in the appropriate circle at the top of each page to indicate the question number.

2. As the human population continues to grow, the demand for animal protein is expected to double by 2050. Animal protein can be obtained from conventional livestock and other sources. The production of all animal protein has environmental costs, as shown in the following graphs. In Figure 1, global warming potential (GWP) is measured in kilograms of carbon dioxide equivalent (kg CO₂-eq.). Carbon dioxide equivalent is a measure of the warming effect of a gas relative to that of carbon dioxide. In Figure 2, land use is measured in meters squared (m²). Global Warming Potential and Land Use from Animal Protein Production Figure 1: Bar graph with y-axis labeled Global Warming Potential (kg CO₂-eq.) with values 0, 20, 40, 60, 80, 100, 120, 140 and x-axis labeled Production of 1 kg of Animal Protein with categories Mealworms, Chicken, Pork, and Beef. Figure 2: Bar graph with y-axis labeled Land Use (m²) with values 0, 20, 40, 60, 80, 100, 120, 140, 160, 180, 200 and x-axis labeled Production of 1 kg of Animal Protein with categories Mealworms, Chicken, Pork, and Beef. (a) Based on the data in the graphs, identify the amount of land required to produce 1 kilogram of chicken protein. Mealworms, the larvae of the darkling beetle, consume grains and decaying plant material. Darkling beetles are an r-selected species, and the entire mealworm can be consumed by humans for protein. (b) Based on the information provided, identify the type of survivorship curve exhibited by the darkling beetle. (c) Explain why the reproductive strategy of the darkling beetle is an advantage for using mealworms as an alternative protein source for the rapidly growing human population. An individual's diet choices affect greenhouse gas emissions and land use. (d) Based on the data in the graphs, explain whether producing 1 kilogram of chicken protein or 1 kilogram of pork protein would cause less environmental damage. Cattle emit methane from fermentation in their digestive systems. The other animals do not emit methane. (e) Based on the data in the graphs, explain why the production of 1 kilogram of beef protein has a different impact on global warming than the production of 1 kilogram of protein from any of the other animals studied would have. Agricultural practices can have negative impacts on rivers and streams. (f) Describe how water quality can be altered by cattle grazing that occurs near a stream or river. (g) Propose a solution to reduce the negative impacts on waterways that result from cattle grazing, while still allowing cattle to graze. (h) Crop production can cause soil erosion. Describe a sustainable agricultural practice used to reduce soil erosion. (i) Justify the use of the sustainable practice described in part (h) by describing an additional advantage, other than the reduction of soil erosion. (j) Crop production around the world is affected by climate change. Describe how crop production could be negatively affected by climate change.

3. Earth's climate has changed over time by the addition of greenhouse gasses to the atmosphere. One approach to mitigate climate change is the use of nuclear power, rather than coal-burning power plants, for electricity generation. (a) Identify a fuel used in a nuclear power plant. (b) Describe a negative environmental impact on nearby bodies of water that is caused by using water for cooling in nuclear power plants. (c) In 2021, 4.1 × 10^12 kilowatt hours (kWh) of commercial electricity was generated in the United States. Nuclear power accounted for 18.9% of the total commercial electricity. Calculate the amount of electricity in kWh generated by nuclear power in the United States in 2021. Show your work. Another approach to reduce greenhouse gas emissions is to switch from coal-burning power plants to natural gas power plants. (d) In addition to reducing greenhouse gas emissions, describe how switching from coal-burning power plants to natural gas power plants will improve air quality. Researchers have proposed large-scale tree planting as a solution to reduce the effects of fossil fuel combustion on global climate change. (e) Justify the proposed solution by explaining an additional advantage, other than the reduction of atmospheric greenhouse gases. (f) 7.4 × 10^7 cubic meters of natural gas were extracted from a large deposit in 2020. An average of 4.76 kWh of electricity can be generated from each cubic meter of natural gas combusted. In 2020, an average home consumed 10,715 kWh of electricity. Calculate how many homes could have been provided with electricity by natural gas extracted from the large deposit in 2020. Show your work. (g) In 2021, 8.99 × 10^11 kWh of electricity was generated through the combustion of coal. One kilogram of carbon dioxide is produced per kWh of electricity generated by combusting coal, while 0.42 kilograms of carbon dioxide is produced by combusting natural gas. Calculate how much less carbon dioxide would have been produced in 2021 if all coal-burning power plants were replaced with natural gas-burning power plants. Show your work. Begin your response to this question at the top of a new page in the separate Free Response booklet and fill in the appropriate circle at the top of each page to indicate the question number.