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

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

Question 1

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

Accepted Answer

Energy flows in a one-way direction through an ecosystem, while chemicals cycle 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 cannot be created or destroyed, only transferred or transformed.

Question 3

A caterpillar eats 200 J of plant material. It assimilates 100 J, uses 67 J for cellular respiration, and produces 33 J of new biomass. What is the production efficiency of the caterpillar?

Accepted Answer

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

Question 4

Which of the following is most likely to be a limiting nutrient in a freshwater lake experiencing low primary production?

Accepted Answer

Phosphorus

Question 5

In the Sargasso Sea, the addition of which micronutrient led to a dramatic increase in primary production, as measured by $$^{14}C $$uptake?

Accepted Answer

Iron (Fe)

Question 6

Which of the following best explains why most food chains are limited in length?

Accepted Answer

Trophic efficiency is low, so only a small fraction of energy is transferred to each successive trophic level.

Question 7

Which process in the nitrogen cycle is responsible for converting $$\mathrm{NO_3$^-}$$ back to atmospheric $$\mathrm{N_2$}$$?

Accepted Answer

Denitrification

Question 8

A forest ecosystem is clear-cut, and researchers observe a significant increase in nutrient loss from the watershed. What is the most likely explanation for this observation?

Accepted Answer

Plants play a key role in retaining nutrients within the ecosystem.

Question 9

Which of the following adaptations would most likely help a plant increase its uptake of a limiting nutrient in nutrient-poor soil?

Accepted Answer

Forming mutualistic associations with mycorrhizal fungi

Question 10

Which of the following statements about the water cycle is correct?

Accepted Answer

Most of the biosphere’s water is contained in the oceans.

Question 11

If the net ecosystem production (NEP) of a forest is negative, what does this indicate about the ecosystem’s carbon balance?

Accepted Answer

The ecosystem is releasing more CO$$_2$$ than it is absorbing and is a carbon source.

Question 12

Which of the following is an example of bioremediation in restoration ecology?

Accepted Answer

Using bacteria to metabolize toxic uranium into an insoluble form

Question 13

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

Accepted Answer

They convert organic matter from all trophic levels to inorganic compounds, returning nutrients to the soil.

Question 14

In a terrestrial ecosystem, which combination of factors would most likely result in the highest net primary production (NPP)?

Accepted Answer

High precipitation, high temperature, and abundant sunlight

Question 15

Which of the following statements about trophic efficiency is correct?

Accepted Answer

Trophic efficiency is the percentage of production transferred from one trophic level to the next, and is typically about 10%.

Question 16

Which of the following is a direct consequence of eutrophication in aquatic ecosystems?

Accepted Answer

Fatally low oxygen concentrations, leading to fish kills

Question 17

Which of the following best explains why eating meat is considered an inefficient way to utilize photosynthetic production?

Accepted Answer

Only a small fraction of energy is transferred to each higher trophic level, so more land is needed to produce the same amount of food energy from meat compared to plants.

Question 18

Which of the following is NOT a process that returns carbon to the atmosphere in the carbon cycle?

Accepted Answer

Photosynthesis

Question 19

Which of the following reservoirs contains the largest amount of phosphorus available to living organisms?

Accepted Answer

Marine sedimentary rocks

Question 20

A region experiences a significant increase in mean annual temperature. According to the data on decomposition rates, what is the most likely effect on the percent of mass lost from leaf litter in this region?

Accepted Answer

The percent of mass lost will increase as temperature rises.

Ecosystem Ecology: Energy Flow and Chemical Cycling

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