Ecology Biogeochemical Nutrient Cycles Questions and Answers 1 — Questions and Answers
Question 1: The conversion of atmospheric nitrogen gas (N2) into ammonia (NH3) or ammonium (NH4+), forms usable by plants, is performed primarily by certain bacteria. What is this critical process called?
- Denitrification
- Nitrification
- Nitrogen Fixation (Correct answer)
- Ammonification
Correct answer: Nitrogen Fixation
Nitrogen fixation is the process where atmospheric nitrogen (N2), which is largely inert, is converted into ammonia (NH3), a form that can be utilized by plants. This is primarily accomplished by specialized nitrogen-fixing bacteria. Denitrification returns N2 to the atmosphere, nitrification converts ammonium to nitrates, and ammonification is the conversion of organic nitrogen back to ammonium.
Question 2: A large-scale deforestation project removes a significant portion of a tropical rainforest. Which of the following describes the most immediate and significant impact on the global carbon cycle?
- A decrease in the rate of carbon sequestration from the atmosphere. (Correct answer)
- An increase in the amount of carbon stored in sedimentary rock.
- A decrease in atmospheric carbon dioxide due to increased soil absorption.
- An increase in the rate of oceanic carbon uptake.
Correct answer: A decrease in the rate of carbon sequestration from the atmosphere.
Forests, particularly large tropical rainforests, act as major carbon sinks by absorbing atmospheric CO2 through photosynthesis. Removing these trees directly reduces the biosphere's capacity to sequester carbon. Furthermore, the burning and decomposition of the cleared vegetation releases large amounts of stored carbon back into the atmosphere as CO2, leading to a net increase in atmospheric levels.
Question 3: Which of the following characteristics most significantly distinguishes the phosphorus cycle from the carbon and nitrogen cycles?
- It is primarily driven by the metabolic activities of microorganisms.
- It lacks a significant gaseous or atmospheric phase. (Correct answer)
- It is significantly and directly impacted by the combustion of fossil fuels.
- It is the fastest of the major biogeochemical cycles.
Correct answer: It lacks a significant gaseous or atmospheric phase.
The phosphorus cycle is a sedimentary cycle, meaning its largest reservoir is in rock and soil, not the atmosphere. Unlike the carbon (CO2) and nitrogen (N2) cycles, the phosphorus cycle does not have a major gaseous component. Phosphorus becomes available very slowly through the weathering of rocks.
Question 4: An ecologist observes a massive algal bloom in a freshwater lake following a period of heavy rainfall that caused significant runoff from a nearby agricultural area. The overgrowth of algae is most likely caused by an excess of which two limiting nutrients commonly found in fertilizers?
- Carbon and Sulfur
- Nitrogen and Phosphorus (Correct answer)
- Potassium and Calcium
- Iron and Magnesium
Correct answer: Nitrogen and Phosphorus
Nitrogen (N) and Phosphorus (P) are the primary limiting nutrients in most aquatic ecosystems. Agricultural fertilizers are rich in N and P to promote crop growth. When excess fertilizer runs off fields into water bodies, it leads to nutrient pollution, causing eutrophication—a process characterized by explosive algal growth (blooms) that can deplete oxygen and harm aquatic life.
Question 5: In the context of the hydrologic cycle, what is the term for the process by which water vapor is released from plants into the atmosphere?
- Infiltration
- Condensation
- Precipitation
- Transpiration (Correct answer)
Correct answer: Transpiration
Transpiration is the process where water is taken up by plant roots and then released as water vapor from small pores (stomata) on the leaves. It is a major pathway for water moving from the terrestrial biosphere back into the atmosphere. Infiltration is water soaking into the ground, condensation is the formation of clouds, and precipitation is water falling back to Earth.
Question 6: Denitrification is a critical step in the nitrogen cycle that returns nitrogen gas to the atmosphere. Which of the following best describes this process?
- Ammonium (NH4+) is converted to nitrate (NO3-) by aerobic bacteria.
- Organic nitrogen is converted to ammonium (NH4+) by decomposers.
- Nitrate (NO3-) is converted to nitrogen gas (N2) by anaerobic bacteria. (Correct answer)
- Nitrogen gas (N2) is converted to ammonia (NH3) by bacteria in root nodules.
Correct answer: Nitrate (NO3-) is converted to nitrogen gas (N2) by anaerobic bacteria.
Denitrification is a microbially-facilitated process where nitrate (NO3−) is reduced to produce molecular nitrogen (N2). This process is carried out by anaerobic bacteria that use nitrate as an electron acceptor for respiration in oxygen-poor environments, such as waterlogged soils. This returns nitrogen to its largest reservoir in the atmosphere.
Ecology Biogeochemical Nutrient Cycles Questions and Answers 1
The conversion of atmospheric nitrogen gas (N2) into ammonia (NH3) or ammonium (NH4+), forms usable by plants, is performed primarily by certain bacteria.
What is this critical process called?