AP Environmental Science Practice Free Response Questions

Preserving high-quality agricultural land is important so that countries can grow enough food to feed their populations.

i) Describe one agricultural practice that can lead to the degradation of agricultural land

- Plowing/tilling the soil increases soil erosion (by breaking up the soil structure) and reduces fertility

- Using monocultures/growing only one crop over and over will deplete the soil of nutrients

- Clearing a field to plant crops can lead to soil desiccation

- Overgrazing by livestock leads to a loss of soil cover and increases soil erosion

ii) Describe a potential solution or technique that can prevent or reduce degradation of agricultural land.

- Contour plowing uses the contours of the land to minimize soil erosion.

- Terracing, growing crops on the side of hills or mountains in a number of flat areas like a series of steps, reduces soil erosion.

- Windbreaks use one or more rows of trees/shrubs to protect an area form wind, which reduces soil erosion.

- Perennial crops remain in the soil year-round/can survive several years, which reduces the need for replanting and improves structure of the soil/reduces erosion.

A less developed country with a rapidly expanding urban population is concerned that its growing urban population will eventually expand to a level where there would not be enough land to grow the food it needs to support its population.

i) Excluding importing food, propose a solution to address the concerns of reduced land on which to grow food.

- Improve yields per hectare through use of genetically modified (GM) crops/high-yield crops/technology, etc

- Plant rooftop gardens in urban areas.

- Use vertical farming techniques

- Grow only crops for food, since plants produce more kilocalories per hectare than livestock

ii) For your solution in (b)(i), explain an additional potential advantage of the solution.

- Improve yields per hectare through use of genetically modified (GM)

· Can preserve remaining habitat for biodiversity

· Reduced use of pesticides/herbicides

· Reduced water requirements

- Plant rooftop gardens in urban areas (solution in (b)(i)).

· Can preserve remaining habitat for biodiversity

· Can insulate buildings

· Can reduce stormwater runoff

· Can offset heat island effect

· Provides green space for urban dwellers

· Can grow crops on existing buildings so no additional land is required

· Can produce food for human consumption/can sell crops for profit

- Use vertical farming techniques (solution in (b)(i))

· Can allow for similar crop yield in a smaller footprint

- Grow only crops for food, since plants produce more kilocalories per hectare than livestock (solution in (b)(i)).

· Can preserve remaining habitat for biodiversity

A table for the population size in the country is shown below.

i) Based on the table, calculate the percent change of the population size in this country between 2009 and 2017. Show your work.

Includes the correct setup, as shown below.

(4.6 − 2.7)2.7 × 100

Includes the correct final calculation, such one of the following:

· 70.37%

· 70.4%

· 70%

An average person in the country needs 2,4502,450 kilocalories (kcal)/day(kcal)/day of food to meet their full nutritional needs. The average number of kcal per hectare (ha)(ha) produced from available food in the country is 15,737,000 kcal/ha 15,737,000 kcal/ha.

i) Calculate the amount of land that would be needed to produce enough kilocalories to feed a person for one year in this developing country. Show your work.

Includes the correct setup, as shown below

2.45 × 10^3 kcal/person / day × 3.65 × 10^2 days / 1 year × 1 ha / 1.5737 × 10^7 kcal

Includes the correct final calculation, such as one of the following:

· 0.0568 hectares per person per year

ii) Calculate how much land would have been needed to feed the population of this country in 2017. Show your work.

Includes the correct setup, as shown below.

(4.6 × 10^6 people )× 5.68 × 10^−2 ha/person / year

includes the correct final calculation, such as one of the following:

· 261,400 ha

Many countries now use centralized sewage treatment plants to treat the wastewater from houses and businesses.

(i) Describe a main goal of primary treatment in a modern sewage treatment plant.

· Large debris/solid waste is physically separated from wastewater using screens/grates/other means.

· Sludge/solid waste settles out in tanks.

ii) Describe a main goal of secondary treatment in a modern sewage treatment plant.

· Microbes (bacteria, fungi, viruses, etc.) are used to breakdown organic matter.

· Aeration of sludge tank aids bacteria in breakdown of organic matter.

iii) Many sewage treatment plants use tertiary treatment as the final step in wastewater treatment. Describe one advantage of this process.

· Removes nutrients, reducing the potential for algal blooms in surface waters.

· Removes phosphorus and nitrogen, decreasing the amount of nutrients in surface waters and reducing the potential for algal blooms.

iv) If a sewage treatment plant malfunctions or if low-income areas lack sanitary waste disposal, raw sewage can be introduced into surface waterways. Describe one potential environmental problem or one potential human health problem that can result from the presence of raw sewage in surface waters.

· Environmental problem: Eutrophication from excess nutrients in water with sewage overflow decreases dissolved oxygen levels in water as decomposers respire while breaking down waste (which stresses or kills aquatic organisms, such as fish).

· Human health problem: Disease-causing organisms/pathogens introduced to surface water could be consumed in drinking water and spread infectious disease (such as cholera, hepatitis A, gastroenteritis, giardia).

v) Identify one water parameter that could be measured to determine whether raw sewage is present in surface waterways.

· Fecal coliform test

· A test for density of fecal coliform bacteria, which while generally harmless, live in human intestines and indicate potential for disease-causing organisms

· A test for disease-causing organisms, such as bacteria or viruses, in water

· A test that measure the amount of oxygen a quantity of water uses over a period of time at a specific temperature

The United States Environmental Protection Agency (EPA) refers to the trash or garbage that can be placed in landfills (landfilled) as municipal solid waste (MSW). MSW can include such items as bottles, cardboard boxes, food, grass clippings, furniture, tires, computers, and appliances. The total MSW generated and the total MSW landfilled from 1960 to 2015 in the United States are shown in the graph below.

i) Describe the trend in total MSW generated from 1960 to 2015.

· The total MSW generated increased.

ii) Compare the trends in the total MSW generated and the total MSW landfilled between 1990 and 2000.

· The total MSW generated increased between 1990 and 2000, but the total MSW sent to landfills decreased slightly during that same period.

iii) Explain a probable reason for the trend in the total MSW landfilled described in (b)(ii).

· Programs to increase the tonnage of MSW recycled, reused, or reduced through conservation measures increased after 1990.

One environmental problem in landfills is that organic materials such as food scraps and yard waste can decompose and produce methane over time. Methane is flammable and can be very dangerous in large concentrations.

(i) Propose a solution to reduce the risk of flammable methane from concentrating in landfills.

· Flare/burn the methane from venting and release by-products into the air

· Collect the methane and burn it to power turbines for electricity generation.

· Incinerate all organic material instead of sending it to a landfill.

· Compost all organic material instead of sending it to a landfill.

ii) Justify your solution proposed in (c)(i) by explaining an additional benefit to the solution besides reducing the amount of flammable methane concentrating in the landfill.

Flare/burn the methane from venting and release by-products into the air (solution in part (c)(i)).

· Can reduce the release of methane (a potent greenhouse gas) into the atmosphere

Collect the methane and burn it to power turbines for electricity generation (solution in part (c)(i)).

· Produce energy/generate electricity for personal or consumer use (economic benefit)

· Capture methane to reduce the release of methane (a potent greenhouse gas) into the atmosphere

· Decrease reliance on coal and other fossil fuels that must be extracted for electricity generation

Incinerate all organic material instead of sending it to a landfill (solution in part (c)(i)).

· Produce energy/generate electricity for personal or consumer use (economic benefit)

Compost all organic material instead of sending it to a landfill (solution in part (c)(i)).

· Use of compost for organic fertilizer for personal or consumer use (ecological or economic benefit)

· Reduce need for synthetic fertilizers in farming by using compost

The diagram below shows the cycling of carbon.

i) Identify a process shown in the diagram that removes carbon from the atmosphere

· Photosynthesis

ii) Identify a process shown in the diagram that sequesters carbon from the atmosphere for a geological period of time.

· The formation of fossil fuels (coal, oil, and natural gas)

· The formation of limestone from sediments in the ocean

iii) Based on the diagram, explain how the combustion of fossil fuels has led to an imbalance in the carbon cycle.

· Carbon that was sequestered in coal or oil or natural gas is combusted and increases the amount of carbon dioxide in the atmosphere.

· Excess carbon is released into the atmosphere from anthropogenic sources, not natural sources, leading to carbon dioxide concentrations that increase faster than can be removed through photosynthesis/absorption into the ocean.

iv) Explain the role of decomposition in the carbon cycle.

· Decomposers cycle carbon from tissue/biomass of dead or decaying organisms into the atmosphere or water as released CO2 from aerobic decomposition

Scientists are interested in researching how carbon dioxide in the oceans is affecting its pH. They design a laboratory experiment in which they inject different concentrations of carbon dioxide into saltwater tanks containing calcium carbonate shells. The tanks were kept at the same, constant temperature. After several days, the scientists measured the pH of the saltwater tanks and observed its effects on the calcium carbonate shells

i) Identify the independent variable in this experiment.

· Concentration of CO2

ii) Describe a control group that could be used in this experiment.

The pH of the tanks before different concentrations of carbon dioxide were injected. (Baseline pH)

iii) Explain the effect of carbon dioxide on the pH of the oceans.

Increased CO2 dissolves in oceans, leading to formation of carbonic acid decreasing the pH of the water/increasing acidification

iv) Describe the effect of water temperature on the amount of dissolved gases in water.

· As water temperature increases, the amount of dissolved oxygen (DO) decreases

v) Describe how the results of the experiment would change if the temperature of the tanks was decreased.

More CO2 would have dissolved in tanks, which would increase acidification/decrease pH/resulting in a larger observed pH change.

vi) Describe how a decrease in ocean pH can affect marine organisms.

· A decrease in pH can cause the calcium carbonate shells of marine organisms to become weak or thin and break easily.