Earth Science B Unit 3 Review

Which biogeochemical cycle can be influenced by human activity and cause eutrophication of a local water supply?

• water cycle

• nitrogen cycle

• population cycle

• carbon cycle

Answer explanation

Eutrophication is the enrichment of nutrients in an aquatic environment that causes excessive growth of aquatic plants, especially algae, which increases bacterial growth and consumption of oxygen, resulting in depletion of oxygen in the environment. Sewage treatment plants release dissolved nitrogen compounds into the surrounding water supply. Adding fertilizers to crops can also be problematic. Many fertilizers are rich in nitrogen compounds, and as we know, plants need these to grow. Excess fertilizers will often enter a local water supply as runoff. Too many nitrogen compounds in an ecosystem can lead to Sewage treatment plants release dissolved nitrogen compounds into the surrounding water supply. Adding fertilizers to crops can also be problematic. Many fertilizers are rich in nitrogen compounds, and as we know, plants need these to grow. Excess fertilizers will often enter a local water supply as runoff. Too many nitrogen compounds in an ecosystem can lead to rapid algae growth.

Which compound is produced when bacteria convert atmospheric nitrogen in the process of nitrogen fixation?

• phosphorous

• nitrogen gas

• nitrate

• ammonia

Answer explanation

Atmospheric nitrogen has the chemical formula N₂. In the process of nitrogen fixation, nitrogen-fixing bacteria change nitrogen into ammonium (NH₃). The ammonium then picks up another hydrogen ion from the soil, becoming NH₄+. 

Which gas is released into the atmosphere through the burning of fossil fuels?

• carbon dioxide

• nitrogen

• carbon monoxide

• oxygen

What role do decomposers play in the cycling of material in a biogeochemical cycle?

• Decomposers make chemicals from the nonliving environment into organic compounds.

• Decomposers incorporate some organic compounds into their bodies and release some back to the environment as waste.

• Decomposers break down organisms to supply the soil, water, and air with inorganic chemicals.

• Decomposers use nonliving processes such as rain and fire to make inorganic chemicals.

Answer explanation

Decomposers like sowbugs and earthworms break down plant and animal waste into nitrogen which is released back into the atmosphere.

During which step of the water cycle is water changed from a vapor state to a liquid state?

• condensation

• transpiration

• evaporation

• precipitationwater cyclew

What impact can deforestation have on the water cycle?

• The amount of nitrogen-fixing bacteria increases.

• Transpiration declines.

• Photosynthesis increases, thereby increasing the amount of carbon dioxide in the air.

• Carbon dioxide is released into the air as trees are burned.

Which process does not involve carbon dioxide entering the atmosphere?

• burning fossil fuels

• volcanic eruptions

• respiration

• photosynthesis

Which result is a concern of the use of fossil fuels?

• eutrophication

• global warming

• increased runoff

• polluted waters

A farmer has concerns about the nitrogen levels in her soils.

What can she do to ensure that the nitrogen bacteria are replenished in the soil?

• Plant a crop of mushrooms to speed up decomposition.

• Plant a crop of legumes, such as clover or alfalfa.

• Plant more plants to increase transpiration.

• Clear cut the area surrounding the field

Answer explanation

Planting legumes is a farming strategy that enriches soil with nitrogen.

Farmers use the nitrogen-fixing capabilities of legumes in crop rotation. Soybeans are legumes. Fields of plants that are not legumes, such as corn or wheat, will deplete the nitrogen in the soil. But, if farmers rotate their crops and plant legumes in that field the next year, nitrogen will become replenished in the soil.

Farmers commonly alternate crops on a yearly basis, planting a nonlegume followed by a legume, to maximize the quality of their soil.

Where is the largest reservoir of carbon on earth located?

• in the atmosphere

• on land

• in freshwater

• in the oceans