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

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

Decomposition → ammonification → nitrification → excretion

Ammonification → denitrification → nitrogen fixation → digestion

2. Ammonification is carried out by ________________

Decomposers breaking down organic nitrogen in dead matter

Nitrifying bacteria in root nodules

Denitrifying bacteria in anaerobic soils

Cyanobacteria in aquatic environments

3. Nutrient cycles are broadly classified into _____________________

Gaseous and sedimentary cycles

Physical and biological cycles

Atmospheric and aquatic cycles

Short-term and long-term cycles

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

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

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

5. Volcanic ash can improve soil fertility by increasing ___________

All of these

Soil structure

Mineral availability

Water retention

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

Stops microbial decomposition

Locks additional carbon into frozen soils

Releases stored carbon as CO₂ and CH₄

Increases phosphorus fixation

7. 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 absorb and release carbon in balance, but deforestation releases stored carbon and reduces future CO₂ absorption

Destroyed forests absorb more CO₂ than intact forests

Intact forests do not exchange carbon with the atmosphere

8. 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

Excess outputs enrich surrounding ecosystems without affecting soil fertility

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

9. The breakdown of volcanic ash releases nutrients through _____________

Respiration

Nitrogen fixation

Weathering

Denitrification

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

Combustion of biomass

Respiration by consumers

Photosynthesis by producers

Decomposition by microbes

Question 1 of 10

Nutrient Cycling MCQs (Quiz 15)

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