Q: A forest ecosystem has a gross primary productivity (GPP) of 12,000 kcal/m²/year and the energy used for respiration (R) is 7,000 kcal/m²/year. What is the net primary productivity (NPP) for this ecosystem?

$$NPP = GPP - R = 12,000 - 7,000 = 5,000 \text{ kcal/m}^2/\text{year}$$

Q: If only 10% of energy is transferred from one trophic level to the next, how much energy would be available to secondary consumers if primary producers capture 10,000 kcal of energy?

$$10,000 \times 0.10 \times 0.10 = 100 \text{ kcal}$$

Question 1

Which of the following best explains why energy transfer between trophic levels in an ecosystem is inefficient?

Accepted Answer

Most energy is lost as heat and molecular waste during metabolic processes, in accordance with the second law of thermodynamics.

Question 2

A forest ecosystem has a gross primary productivity (GPP) of 12,000 kcal/m²/year and the energy used for respiration (R) is 7,000 kcal/m²/year. What is the net primary productivity (NPP) for this ecosystem?

Accepted Answer

$$NPP = GPP - R = 12,000 - 7,000 = 5,000 	ext{ kcal/m}^2/	ext{year}$$

Question 3

Which of the following statements about decomposers is correct?

Accepted Answer

Decomposers recycle nutrients from dead organic matter, making them available to primary producers and maintaining ecosystem functioning.

Question 4

In a food web, why does biomagnification of toxins such as mercury or DDT occur at higher trophic levels?

Accepted Answer

Toxins accumulate in organisms and are not easily broken down or excreted, so their concentration increases as they move up the food chain.

Question 5

Which process is primarily responsible for moving carbon from the atmosphere into the biotic reservoir of an ecosystem?

Accepted Answer

Photosynthesis by autotrophic organisms

Question 6

A scientist observes that in a tropical rainforest, there is little accumulation of detritus in the soil. What is the most likely explanation for this observation?

Accepted Answer

High moisture and temperature increase the rate of decomposition, so detritus is rapidly recycled into new plant growth.

Question 7

Which of the following best describes the difference between energy flow and nutrient cycling in ecosystems?

Accepted Answer

Energy flows in one direction and is eventually lost as heat, while nutrients cycle between biotic and abiotic reservoirs.

Question 8

Which human activity has most directly increased the amount of nitrogen available in aquatic ecosystems, often leading to eutrophication and dead zones?

Accepted Answer

Application of fertilizers containing nitrogen and phosphorus

Question 9

If only 10% of energy is transferred from one trophic level to the next, how much energy would be available to secondary consumers if primary producers capture 10,000 kcal of energy?

Accepted Answer

$$10,000 	imes 0.10 	imes 0.10 = 100 	ext{ kcal}$$

Question 10

Which of the following is a direct consequence of the law of thermodynamics in ecosystem energy flow?

Accepted Answer

Some energy is always lost as heat during metabolic processes, limiting the number of trophic levels.

Question 11

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

Accepted Answer

Atmospheric nitrogen gas ($$N_2)$$

Question 12

How does deforestation contribute to increased atmospheric carbon dioxide ($$CO_2) $$levels?

Accepted Answer

It reduces the number of primary producers that can fix $$CO_2$$ via photosynthesis, and releases stored carbon when trees are burned or decay.

Question 13

Which of the following best describes the role of water in ecosystem nutrient cycling?

Accepted Answer

Water movement through evaporation, precipitation, and percolation transports dissolved nutrients across ecosystems.

Question 14

Which of the following is a likely effect of global climate change on biodiversity?

Accepted Answer

Shifts in geographic ranges, changes in phenology, and increased risk of extinction for some species.

Question 15

Which process is responsible for converting atmospheric nitrogen ($$N_2) $$into biologically usable forms such as ammonium ($$NH_4$$^+$$) or nitrate (NO_3$^-$$)?

Accepted Answer

Nitrogen fixation by microorganisms

Question 16

A city replaces a large area of forest with concrete buildings. What is a likely consequence for the local water cycle?

Accepted Answer

Reduced percolation and groundwater recharge, increased surface runoff and nutrient loss.

Question 17

Which of the following is a density-dependent constraint on human population size related to trophic levels?

Accepted Answer

More humans can be supported on a plant-based diet than on a meat-based diet due to greater energy availability at lower trophic levels.

Question 18

Which of the following is a correct statement about the difference between weather and climate?

Accepted Answer

Weather refers to short-term, variable atmospheric conditions; climate refers to long-term average patterns.

Question 19

Which of the following greenhouse gases is most directly linked to human activities such as fossil fuel burning and deforestation?

Accepted Answer

Carbon dioxide ($$CO_2)$$

Energy Flow and Nutrient Cycling in Ecosystem Ecology

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