$$\mathrm{NPP} = \mathrm{GPP} - \text{Respiration}$$

Question 1

Which of the following best explains why the Earth is considered a closed system for matter but an open system for energy?

Accepted Answer

Matter cycles within the Earth, while energy enters as sunlight and leaves as heat.

Question 2

Gross primary production (GPP) in an ecosystem is best defined as:

Accepted Answer

The total amount of carbon fixed by autotrophs.

Question 3

Net primary production (NPP) can be calculated using which of the following equations?

Accepted Answer

$$\mathrm{NPP} = \mathrm{GPP} - 	ext{Respiration}$$

Question 4

In terrestrial biomes such as tundra and temperate grasslands, plants allocate a higher percentage of NPP to root formation primarily because:

Accepted Answer

Soil nutrients are scarce, so increased root surface area maximizes nutrient uptake.

Question 5

Which of the following best describes the relationship between actual evapotranspiration and net primary production in terrestrial ecosystems?

Accepted Answer

As actual evapotranspiration increases, net primary production also increases.

Question 6

Ecological (trophic) efficiency is typically low because:

Accepted Answer

About 90% of energy is lost at each trophic transfer, mainly as heat and waste.

Question 7

Which of the following is a correct sequence of processes in the nitrogen cycle that makes atmospheric nitrogen available to plants?

Accepted Answer

Nitrogen fixation $$\rightarrow$$ Assimilation $$\rightarrow$$ Mineralization

Question 8

Which process is primarily responsible for the formation of 'dead zones' in aquatic environments such as the Gulf of Mexico?

Accepted Answer

Eutrophication caused by excess nitrogen and phosphorus runoff from agriculture.

Question 9

Why can some aquatic ecosystems have an inverted biomass pyramid, where the biomass of primary producers is less than that of primary consumers?

Accepted Answer

Primary producers like phytoplankton are rapidly consumed and have high turnover rates.

Question 10

Which of the following nutrients is most likely to be limiting in freshwater ecosystems?

Accepted Answer

Phosphorus

Question 11

The Haber-Bosch process is significant in global nutrient cycles because it:

Accepted Answer

Artificially fixes atmospheric nitrogen into forms usable by plants, increasing fertilizer production.

Question 12

Which of the following best explains why tropical forests allocate more NPP to leaf formation compared to roots?

Accepted Answer

Light is limiting in lower canopy layers, so more leaves maximize photosynthesis.

Question 13

Which of the following is NOT a major reservoir for phosphorus in the global phosphorus cycle?

Accepted Answer

Atmosphere

Question 14

Which of the following equations correctly represents the relationship between energy transfer and trophic efficiency?

Accepted Answer

$$	ext{Energy at trophic level } n = 	ext{Energy at trophic level } (n-1) 	imes 	ext{Trophic efficiency}$$

Question 15

Which of the following best describes the role of decomposers in nutrient cycling?

Accepted Answer

They break down organic matter, releasing nutrients back into the ecosystem.

Question 16

A lake receives a large input of phosphorus from agricultural runoff. Which sequence of events is most likely to occur?

Accepted Answer

Algal bloom $$\rightarrow$$ Increased decomposition $$\rightarrow$$ Oxygen depletion $$\rightarrow$$ Fish die-off

Question 17

Which of the following statements about limiting nutrients is correct?

Accepted Answer

A limiting nutrient is the essential nutrient in shortest supply relative to the needs of primary producers.

Question 18

Which of the following is a real-world example of how human activity has altered the nitrogen cycle?

Accepted Answer

The widespread use of synthetic fertilizers has increased nitrogen runoff, leading to eutrophication.

Question 19

Which of the following best explains why net primary production is highest at intermediate stages of ecological succession?

Accepted Answer

Intermediate communities have greater biomass and diversity, maximizing photosynthesis.

Question 20

Which of the following is a physiological reason why nitrogen is often a limiting nutrient for primary production?

Accepted Answer

Most atmospheric nitrogen is in a form that is energetically costly for organisms to use.

7.3 Energy Flow and Nutrient Cycling in Ecosystems

Study Guide - Practice Questions