Question 1

Which of the following best explains why phosphorus is often a limiting nutrient in aquatic ecosystems?

Accepted Answer

Phosphorus is primarily found in mineral deposits and marine sediments, making it less available to organisms.

Question 2

Which process in the nitrogen cycle is responsible for converting nitrate ($$NO_3$$^-$$) back into atmospheric nitrogen gas (N_2$) under anaerobic conditions?

Accepted Answer

Denitrification

Question 3

A farmer applies large amounts of nitrogen fertilizer to his fields. Which of the following is a likely consequence for a nearby lake?

Accepted Answer

Eutrophication due to nutrient pollution

Question 4

Which of the following combinations would result in the fastest rate of decomposition of plant litter in a terrestrial ecosystem?

Accepted Answer

High temperature, high moisture, high nitrogen content

Question 5

Which human activity directly increases the amount of carbon dioxide ($$CO_2) in $$the atmosphere, contributing to global warming?

Accepted Answer

Burning fossil fuels

Question 6

In the carbon cycle, which process removes $$CO_2$$ from the atmosphere and incorporates it into organic molecules?

Accepted Answer

Photosynthesis

Question 7

Which of the following best describes the role of nitrogen-fixing bacteria in the nitrogen cycle?

Accepted Answer

They convert atmospheric nitrogen gas ($$N_2) $$into ammonia ($$NH_3).$$

Question 8

A researcher finds that leaves with a high lignin content decompose slowly in a stream. What is the most likely explanation?

Accepted Answer

High lignin content inhibits fungal colonization, slowing decomposition.

Question 9

Which of the following is NOT a direct consequence of large-scale deforestation?

Accepted Answer

Decreased atmospheric $$CO_2$$ levels

Question 10

Which of the following scenarios would most likely result in increased nutrient export from a forest ecosystem?

Accepted Answer

Clear-cutting of trees followed by heavy rainfall

Question 11

Which of the following best explains why the global phosphorus cycle does NOT include a substantial atmospheric pool?

Accepted Answer

Phosphorus does not form significant volatile compounds under natural conditions.

Question 12

Which of the following would most likely increase the rate of mineralization in a terrestrial ecosystem?

Accepted Answer

Increasing temperature and moisture

Question 13

A scientist observes that after a flood, a stream exports more phosphorus than it receives. What is the most likely explanation?

Accepted Answer

Flooding increases the export of phosphorus by washing it out of the ecosystem.

Question 14

Which of the following is a direct effect of burning fossil fuels on the nitrogen cycle?

Accepted Answer

Release of nitrous oxides ($$N_2O) $$into the atmosphere, contributing to acid rain

Question 15

Which of the following would most likely result from introducing a nitrogen-fixing tree species into an ecosystem where it was previously absent?

Accepted Answer

Increased nitrogen input, altering nutrient dynamics

Question 16

Which of the following best describes the relationship between grazing intensity and nutrient cycling in the Serengeti Plain, as found by MacNaughton?

Accepted Answer

Higher grazing intensity speeds up nutrient cycling and plant biomass turnover.

Question 17

Which of the following factors would most likely decrease the rate of decomposition in a temperate forest ecosystem?

Accepted Answer

Increasing lignin content in plant litter

Question 18

Which of the following is a correct sequence of processes in the nitrogen cycle, starting with atmospheric $$N_2$$?

Accepted Answer

Nitrogen fixation $$\rightarrow$$ Ammonification $$\rightarrow$$ Nitrification $$\rightarrow$$ Denitrification

Question 19

Which of the following best explains why leaves with a low carbon:nitrogen ratio decompose faster than those with a high ratio?

Accepted Answer

Low carbon:nitrogen ratio means more nitrogen is available for decomposers, enhancing decomposition.

Question 20

Which of the following is a likely effect of pocket gophers bringing nitrogen-poor subsoil to the surface?

Accepted Answer

Decreased soil nitrogen content at the surface, increasing heterogeneity

ch 19: Nutrient Cycling and Retention: Carbon, Nitrogen, and Phosphorus Cycles

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