Q: A caterpillar eats a leaf containing 200 J of energy. It assimilates 100 J, uses 67 J for respiration, and produces 33 J of new biomass. What is the production efficiency of the caterpillar?

$$\text{Production efficiency} = \frac{33}{100} \times 100\% = 33\%$$

Question 1

Which of the following best describes the difference between energy flow and chemical cycling in an ecosystem?

Accepted Answer

Energy flows through the ecosystem and is lost as heat, while matter cycles within the ecosystem.

Question 2

According to the first law of thermodynamics, which of the following statements is true regarding energy in ecosystems?

Accepted Answer

Energy is transformed from one form to another but cannot be created or destroyed.

Question 3

A lake receives excess nutrient runoff from nearby farms, resulting in a rapid increase in algal growth. What is the most likely consequence for the lake ecosystem?

Accepted Answer

Eutrophication leading to anoxia and loss of fish species.

Question 4

Which nutrient most commonly limits primary production in terrestrial ecosystems?

Accepted Answer

Nitrogen

Question 5

If the gross primary production (GPP) of an ecosystem is $$5000\ \mathrm{J/m^2$\cdot yr}$$ and the energy used by primary producers for respiration is $$2000\ \mathrm{J/m^2$\cdot yr}$$, what is the net primary production (NPP)?

Accepted Answer

$$NPP = 3000\ \mathrm{J/m^2$\cdot yr}$$

Question 6

A caterpillar eats a leaf containing 200 J of energy. It assimilates 100 J, uses 67 J for respiration, and produces 33 J of new biomass. What is the production efficiency of the caterpillar?

Accepted Answer

$$	ext{Production efficiency} = \frac{33}{100} 	imes 100\% = 33\%$$

Question 7

Why do birds and mammals typically have lower production efficiencies (1–3%) compared to insects and microorganisms?

Accepted Answer

They use a large proportion of their assimilated energy to maintain a constant body temperature (endothermy).

Question 8

In a typical energy pyramid, if 1,000,000 J of sunlight is captured by primary producers, approximately how much energy is available to tertiary consumers?

Accepted Answer

10 J

Question 9

Which of the following adaptations helps plants reduce nutrient limitation in terrestrial ecosystems?

Accepted Answer

Forming mutualisms with mycorrhizal fungi

Question 10

Which process in the nitrogen cycle converts atmospheric $$N_2$$ into a form usable by plants?

Accepted Answer

Nitrogen fixation

Question 11

A scientist adds iron to a region of the Sargasso Sea and observes a dramatic increase in phytoplankton growth. What does this experiment demonstrate about primary production in this region?

Accepted Answer

Iron is a limiting nutrient for primary production in the Sargasso Sea.

Question 12

Which of the following best explains why some aquatic ecosystems have inverted biomass pyramids?

Accepted Answer

Primary producers are consumed so quickly that their standing biomass is lower than that of primary consumers.

Question 13

Which of the following is a consequence of the law of conservation of mass in ecosystems?

Accepted Answer

Chemical elements are continually recycled within ecosystems.

Question 14

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

Accepted Answer

Atmosphere

Question 15

A farmer wants to maximize crop yield in an old, weathered soil. Which nutrient is most likely to be limiting, and what adaptation could help the plants?

Accepted Answer

Phosphorus; mutualism with mycorrhizal fungi

Question 16

Which process in the nitrogen cycle returns nitrogen to the atmosphere as $$N_2$$ gas?

Accepted Answer

Denitrification

Question 17

If humans shifted to a diet consisting only of plant material, what would be the most likely ecological consequence?

Accepted Answer

More people could be supported by the same amount of agricultural land.

Question 18

Which of the following best describes the role of detritivores in an ecosystem?

Accepted Answer

They recycle nutrients by breaking down dead organic matter.

Question 19

Which of the following equations correctly represents the calculation of production efficiency for an organism?

Accepted Answer

$$	ext{Production efficiency} = \frac{	ext{Net secondary production}}{	ext{Assimilation of primary production}} 	imes 100\%$$

Ecosystem Dynamics: Energy Flow and Nutrient Cycling

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