Q: A forest ecosystem receives 10,000 J of sunlight. If only 1,000 J is converted to chemical energy by primary producers, and only 100 J is available to primary consumers, what is the trophic efficiency between primary producers and primary consumers?

$$ \frac{100}{1,000} \times 100 = 10\% $$

Q: A scientist measures the net primary production (NPP) of a grassland as 500 g/m$$^2/$$year and the gross primary production (GPP) as 1,200 g/m$$^2/$$year. What is the ecosystem's respiration (R)?

$$ R = GPP - NPP = 1,200 - 500 = 700 \ \text{g/m}^2/\text{year} $$

Question 1

Which law of thermodynamics best explains why energy transfer between trophic levels in an ecosystem is not 100% efficient?

Accepted Answer

The second law of thermodynamics, which states that every energy transfer increases the entropy of the universe.

Question 2

A forest ecosystem receives 10,000 J of sunlight. If only 1,000 J is converted to chemical energy by primary producers, and only 100 J is available to primary consumers, what is the trophic efficiency between primary producers and primary consumers?

Accepted Answer

$$ \frac{100}{1,000} 	imes 100 = 10\% $$

Question 3

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

Accepted Answer

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

Question 4

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

Accepted Answer

Nitrogen-fixing bacteria

Question 5

A lake ecosystem is experiencing eutrophication due to excess nitrogen runoff. Which process is most directly responsible for the increased growth of algae?

Accepted Answer

Primary production by autotrophs

Question 6

Which of the following best explains why energy pyramids are always upright, but pyramids of biomass or numbers can sometimes be inverted?

Accepted Answer

Energy is lost as heat at each trophic level, but biomass and numbers can vary depending on the ecosystem.

Question 7

Which of the following statements about nitrogen fixation is correct?

Accepted Answer

Nitrogen fixation converts atmospheric $$ N_2$ $$ into ammonia ($$ NH_3$ ) $$usable by plants.

Question 8

In a restoration ecology project, which of the following would be considered an example of biological augmentation?

Accepted Answer

Adding nitrogen-fixing bacteria to improve soil fertility.

Question 9

Which of the following best describes the main goal of restoration ecology?

Accepted Answer

To return degraded ecosystems to as close to their original state as possible.

Question 10

A scientist measures the net primary production (NPP) of a grassland as 500 g/m$$^2/$$year and the gross primary production (GPP) as 1,200 g/m$$^2/$$year. What is the ecosystem's respiration (R)?

Accepted Answer

$$ R = GPP - NPP = 1,200 - 500 = 700 \ 	ext{g/m}^2/	ext{year} $$

Question 11

Which of the following best explains why phosphorus is often a limiting nutrient in freshwater ecosystems?

Accepted Answer

Phosphorus cycles very slowly because it has no significant atmospheric component.

Question 12

Which of the following is an example of a biogeochemical process that cycles water in ecosystems?

Accepted Answer

Transpiration from plant leaves

Question 13

If a food chain consists of grass (producer), grasshopper (primary consumer), frog (secondary consumer), and snake (tertiary consumer), which organism would you expect to have the lowest biomass?

Accepted Answer

Snake

Question 14

Which of the following best describes the difference between primary and secondary production in an ecosystem?

Accepted Answer

Primary production is the amount of energy stored by autotrophs, while secondary production is the amount of energy stored by heterotrophs.

Question 15

Which of the following scenarios would most likely increase the rate of decomposition in a forest ecosystem?

Accepted Answer

Increased moisture and moderate temperatures

Question 16

Which of the following is a correct statement about the water cycle?

Accepted Answer

Evaporation from oceans and transpiration from plants both return water vapor to the atmosphere.

Question 17

Which of the following best explains why only a small fraction of energy is transferred from one trophic level to the next?

Accepted Answer

Most energy is used for cellular respiration and lost as heat, according to the second law of thermodynamics.

Question 18

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

Accepted Answer

Planting sunflowers to absorb heavy metals from contaminated soil.

Question 19

Which of the following best describes the process of denitrification in the nitrogen cycle?

Accepted Answer

Conversion of $$ NO_3$^-  to$$ $$ N_2$ $$ gas by bacteria, returning nitrogen to the atmosphere.

Question 20

Which of the following would most likely result from the removal of decomposers from an ecosystem?

Accepted Answer

Accumulation of dead organic matter and decreased nutrient cycling

Ecosystem Energy Flow, Nutrient Cycling, and Restoration: Study Notes

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