Ecology Biogeochemical Cycles 3 — Questions and Answers
Question 1: Which of the following best describes a 'sink' in a biogeochemical cycle?
- A source that releases nutrients into the environment
- A reservoir that accumulates more of a substance than it releases (Correct answer)
- A pathway connecting two nutrient pools
- An organism that breaks down organic matter
Correct answer: A reservoir that accumulates more of a substance than it releases
A sink is any reservoir that absorbs and stores more of a substance than it releases over a given time period.
Question 2: What happens to the carbon stored in peat bogs when they are drained and burned?
- It enters the rock cycle as limestone
- It is released as CO₂, contributing to atmospheric greenhouse gases (Correct answer)
- It is converted to methane and stored underground
- It is absorbed by surrounding vegetation
Correct answer: It is released as CO₂, contributing to atmospheric greenhouse gases
Draining and burning peat bogs releases centuries of stored carbon as CO₂, making them significant sources of greenhouse gas emissions.
Question 3: Which step in the nitrogen cycle converts ammonium (NH₄⁺) into nitrite (NO₂⁻) and then nitrate (NO₃⁻)?
- Ammonification
- Denitrification
- Nitrification (Correct answer)
- Nitrogen fixation
Correct answer: Nitrification
Nitrification is a two-step aerobic process performed by bacteria like Nitrosomonas and Nitrobacter that oxidizes ammonium to nitrite then nitrate.
Question 4: How does the hydrological (water) cycle interact with the phosphorus cycle?
- Evaporation concentrates phosphorus in the atmosphere
- Precipitation and runoff transport dissolved phosphate from land to aquatic systems (Correct answer)
- Water vapor carries phosphorus between continents
- Groundwater converts inorganic phosphorus to organic forms
Correct answer: Precipitation and runoff transport dissolved phosphate from land to aquatic systems
Precipitation and surface runoff erode and transport phosphate ions from soils and rocks into rivers, lakes, and eventually the ocean.
Question 5: Eutrophication of lakes is most directly caused by excess input of which nutrients?
- Carbon and sulfur
- Nitrogen and phosphorus (Correct answer)
- Calcium and magnesium
- Iron and manganese
Correct answer: Nitrogen and phosphorus
Excess nitrogen and phosphorus from agricultural runoff fuel algal blooms in lakes, leading to oxygen depletion when algae decompose.
Question 6: What is the primary pathway by which carbon moves from the atmosphere into terrestrial ecosystems?
- Weathering of carbonate rocks
- Photosynthesis by plants and other autotrophs (Correct answer)
- Dissolution into rainwater forming carbonic acid
- Volcanic outgassing and reabsorption
Correct answer: Photosynthesis by plants and other autotrophs
Photosynthesis is the main biological pump that removes CO₂ from the atmosphere and incorporates it into organic molecules.
Question 7: Which biogeochemical cycle is most closely linked to the formation of acid rain?
- The phosphorus cycle
- The carbon cycle
- The sulfur cycle (Correct answer)
- The calcium cycle
Correct answer: The sulfur cycle
SO₂ emissions from fossil fuel combustion react with water vapor to form sulfuric acid, which falls as acid rain.
Ecology Biogeochemical Cycles 3
Which of the following best describes a 'sink' in a biogeochemical cycle?