Nutrient Cycling MCQs (Quiz 15)

1. Researchers add ¹⁵N-labeled nitrate (¹⁵NO₃⁻) to soil and later detect ¹⁵N in herbivore proteins. Which sequence best explains this transfer of nitrogen?

Nitrogen fixation → nitrification → denitrification → excretion

Ammonification → denitrification → nitrogen fixation → digestion

Decomposition → ammonification → nitrification → excretion

Absorption of ¹⁵NO₃⁻ by plant roots → assimilation into plant proteins → consumption by herbivores → assimilation into animal tissues

2. What is the primary source of carbon entering most food webs?

Photosynthesis by producers

Combustion of biomass

Respiration by consumers

Decomposition by microbes

3. Permafrost thawing is a major climate concern because it ___________

Locks additional carbon into frozen soils

Increases phosphorus fixation

Stops microbial decomposition

Releases stored carbon as CO₂ and CH₄

4. Nutrient cycles are broadly classified into _____________________

Gaseous and sedimentary cycles

Short-term and long-term cycles

Physical and biological cycles

Atmospheric and aquatic cycles

5. Ammonification is carried out by ________________

Decomposers breaking down organic nitrogen in dead matter

Cyanobacteria in aquatic environments

Denitrifying bacteria in anaerobic soils

Nitrifying bacteria in root nodules

6. The breakdown of volcanic ash releases nutrients through _____________

Denitrification

Weathering

Respiration

Nitrogen fixation

7. An agricultural field has nutrient outputs that consistently exceed nutrient inputs over several growing seasons. What does this indicate?

The field has a balanced nutrient budget, indicating sustainable productivity

The field has a negative nutrient budget, indicating progressive soil nutrient depletion and declining soil fertility over time

High outputs suggest accelerated decomposition that improves soil nutrient levels

Excess outputs enrich surrounding ecosystems without affecting soil fertility

8. Why are tropical rainforests considered carbon neutral when intact, but a major source of climate change when destroyed?

Deforestation increases carbon storage in vegetation

Intact forests do not exchange carbon with the atmosphere

Intact forests absorb and release carbon in balance, but deforestation releases stored carbon and reduces future CO₂ absorption

Destroyed forests absorb more CO₂ than intact forests

9. Which of the following best explains why ecosystems would collapse without decomposers?

Rainfall would decrease due to reduced transpiration from nutrient-starved plants

Consumers would lose their primary food source as herbivore populations declined

Producers would no longer be able to photosynthesize without decomposer byproducts

Inorganic nutrients would remain locked in dead organic matter and become unavailable to producers, disrupting the entire nutrient cycle

10. Volcanic ash can improve soil fertility by increasing ___________

Mineral availability

Water retention

Soil structure

All of these

Question 1 of 10

Nutrient Cycling MCQs (Quiz 15)

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