Ecology Biogeochemical Cycles 2 — Questions and Answers
Question 1: Which process converts atmospheric nitrogen (N₂) into ammonia (NH₃) that plants can use?
- Nitrification
- Nitrogen fixation (Correct answer)
- Denitrification
- Ammonification
Correct answer: Nitrogen fixation
Nitrogen fixation, carried out by bacteria like Rhizobium, converts inert N₂ gas into ammonia that plants can absorb.
Question 2: In the phosphorus cycle, what is the primary reservoir of phosphorus on Earth?
- The atmosphere
- Ocean water
- Rocks and sediments (Correct answer)
- Living organisms
Correct answer: Rocks and sediments
Unlike carbon and nitrogen, phosphorus has no significant atmospheric reservoir and is stored primarily in rocks and sediments.
Question 3: What process do decomposers perform that is essential to the nitrogen cycle?
- Nitrification
- Denitrification
- Ammonification (Correct answer)
- Nitrogen fixation
Correct answer: Ammonification
Decomposers break down organic nitrogen in dead organisms into ammonia (NH₃) through ammonification.
Question 4: Which human activity has most dramatically increased the rate of nitrogen entering ecosystems?
- Burning fossil fuels
- Synthetic fertilizer production via the Haber-Bosch process (Correct answer)
- Deforestation
- Irrigation
Correct answer: Synthetic fertilizer production via the Haber-Bosch process
The Haber-Bosch process industrially fixes atmospheric nitrogen into ammonia for fertilizers, roughly doubling natural nitrogen fixation rates globally.
Question 5: During the sulfur cycle, which process releases sulfur dioxide (SO₂) into the atmosphere?
- Volcanic eruptions and fossil fuel combustion (Correct answer)
- Photosynthesis
- Decomposition of plant cellulose
- Nitrogen fixation
Correct answer: Volcanic eruptions and fossil fuel combustion
Volcanic eruptions and burning sulfur-containing fossil fuels are major pathways releasing SO₂ into the atmosphere.
Question 6: What role do mycorrhizal fungi play in the phosphorus cycle?
- They fix atmospheric phosphorus
- They extend plant root surface area to absorb more phosphate from soil (Correct answer)
- They convert phosphate into phosphine gas
- They store phosphorus in their fruiting bodies for later use
Correct answer: They extend plant root surface area to absorb more phosphate from soil
Mycorrhizal fungi form symbiotic networks with plant roots, dramatically extending their reach to absorb phosphate ions from soil.
Question 7: In a wetland ecosystem, which microbial process removes bioavailable nitrogen by converting nitrate back to N₂ gas?
- Nitrification
- Assimilation
- Denitrification (Correct answer)
- Ammonification
Correct answer: Denitrification
Denitrification by anaerobic bacteria in waterlogged soils converts nitrate (NO₃⁻) back to N₂ gas, removing it from the ecosystem.
Ecology Biogeochemical Cycles 2
Which process converts atmospheric nitrogen (N₂) into ammonia (NH₃) that plants can use?