Question 1

Which of the following best explains why energy transfer between trophic levels in an ecosystem is typically only about 10% efficient?

Accepted Answer

Most of the energy is used for cellular respiration and lost as heat at each trophic level.

Question 2

A caterpillar eats a leaf containing 1000 J of chemical energy. If only 15% of this energy is converted to caterpillar biomass, how much energy is available to a bird that eats the caterpillar?

Accepted Answer

$$150 \ \mathrm{J}$$

Question 3

Which of the following statements about biogeochemical cycles is correct?

Accepted Answer

The phosphorus cycle does not have a significant atmospheric component.

Question 4

Which process is primarily responsible for returning carbon dioxide to the atmosphere in the carbon cycle?

Accepted Answer

Cellular respiration

Question 5

Why is phosphorus often a limiting nutrient in terrestrial ecosystems?

Accepted Answer

Phosphorus is released slowly from rocks by weathering and is not abundant in the atmosphere.

Question 6

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

Accepted Answer

They break down organic matter, releasing nutrients back into the soil and atmosphere.

Question 7

A farmer applies a large amount of phosphate fertilizer to a field. Which of the following is a likely consequence for a nearby aquatic ecosystem?

Accepted Answer

Increased phosphate runoff may lead to eutrophication and algal blooms.

Question 8

Which of the following is a correct sequence of events in the nitrogen cycle?

Accepted Answer

Nitrogen fixation $$\rightarrow$$ assimilation $$\rightarrow$$ ammonification $$\rightarrow$$ denitrification

Question 9

If the net primary production (NPP) of a grassland ecosystem is $$800 \ \mathrm{g/m^2$/yr}$$ and the gross primary production (GPP) is $$2000 \ \mathrm{g/m^2$/yr}$$, what is the amount of energy used by producers for respiration?

Accepted Answer

$$1200 \ \mathrm{g/m^2$/yr}$$

Question 10

Which of the following best explains why the open ocean, despite its vast area, has relatively low net primary production per unit area?

Accepted Answer

Nutrient availability limits the growth of producers in most ocean regions.

Question 11

A scientist is studying a food chain: grass $$\rightarrow$$ grasshopper $$\rightarrow$$ frog $$\rightarrow$$ snake. If the grass produces $$10,000 \ \mathrm{J} of $$energy, approximately how much energy would be available to the snake?

Accepted Answer

$$10 \ \mathrm{J}$$

Question 12

Which of the following is an example of an abiotic reservoir in a biogeochemical cycle?

Accepted Answer

Atmospheric carbon dioxide

Question 13

Why is nitrogen fixation a critical process in the nitrogen cycle?

Accepted Answer

It converts atmospheric $$\mathrm{N_2$}$$ into forms usable by living organisms.

Question 14

Which of the following would most likely increase the rate of phosphorus cycling in an ecosystem?

Accepted Answer

Increased weathering of rocks due to heavy rainfall

Question 15

A lake receives runoff from a fertilized field, resulting in a rapid increase in algal growth. This is an example of which ecological phenomenon?

Accepted Answer

Eutrophication

Question 16

Which of the following best describes the relationship between photosynthesis and cellular respiration in the global carbon cycle?

Accepted Answer

Photosynthesis removes $$\mathrm{CO_2$}$$ from the atmosphere, while cellular respiration returns it.

Question 17

Which of the following is a direct consequence of the increased burning of fossil fuels?

Accepted Answer

Increased atmospheric $$\mathrm{CO_2$}$$ levels

Question 18

Which of the following best explains why the phosphorus cycle is considered 'sedimentary' rather than 'gaseous'?

Accepted Answer

Phosphorus does not have a significant atmospheric component and cycles mainly through rocks and soil.

Energy Flow and Biogeochemical Cycles in Ecosystems

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