Question 1

Which of the following is a consequence of biomagnification?

Accepted Answer

Biomagnification is the increase in concentration of toxic chemicals as you move up the food chain. This means that top-level predators, who consume many lower-level consumers, will accumulate the most toxins in their tissues. As a result, they are at greater risk of harm from these toxins than primary consumers.

Question 2

Why is terrestrial productivity higher in equatorial climates?

Accepted Answer

Terrestrial productivity is influenced by a range of factors, including temperature, water availability, and sunlight. Equatorial climates tend to have high temperatures and abundant water, which can increase productivity. Additionally, these regions receive consistently high amounts of sunlight throughout the year, which can also boost productivity. Therefore, the most likely explanation is that a combination of these factors contributes to higher productivity in equatorial climates.

Question 3

Nitrogen is available to plants mostly in the form of ________.

Accepted Answer

Nitrogen is most commonly available to plants in the form of nitrate and ammonium ions in the soil. These ions are produced through the process of nitrogen fixation, where specialized bacteria convert atmospheric nitrogen into a form that can be used by plants. Nitrite ions are also present in the soil, but in much lower concentrations than nitrate and ammonium ions. Uric acid from animal excretions and nucleic acids from decomposing plants and animals can also release nitrogen into the soil, but these sources are not as common as nitrate and ammonium ions. Nitrogen in the atmosphere cannot be utilized by most plants and must first be converted into a usable form.

Question 4

-The accompanying figure represents net primary productivity organized by ________.

Accepted Answer

The term "net primary productivity" refers to the amount of organic material (biomass) that plants produce through photosynthesis, minus the energy they use for respiration. This concept is often analyzed within specific biomes, which are distinct biological communities that have formed in response to a shared climate. Therefore, organizing net primary productivity by biome is the correct approach, as it allows for the comparison of productivity across different ecosystems that have similar environmental conditions.

Question 5

If the flow of energy in an arctic ecosystem goes through a simple food chain, perhaps involving humans, starting from phytoplankton to zooplankton to fish to seals to polar bears, then which of the following could be TRUE?

Accepted Answer

In general, lower trophic levels in a food chain have a higher biomass and are more abundant than higher trophic levels. Therefore, it is likely that there are more fish than seals in this arctic ecosystem, making fish a potentially larger food source for humans than seal meat. The other answer choices are not supported by the information provided in the question or are likely to be false.

Question 6

Consider the food chain of grass → grasshopper → mouse → snake → hawk. About how much of the chemical energy fixed by photosynthesis of the grass (100 percent) is available to the hawk?

Accepted Answer

In a typical food chain, only about 10% of the energy from one trophic level is transferred to the next. Starting with 100% at the grass level, the energy available to the grasshopper is about 10%, to the mouse 1%, to the snake 0.1%, and finally to the hawk only about 0.01%.

Question 7

-Consider the global nitrogen cycle depicted in the accompanying figure. What is the limiting portion of the cycle for plants?

Accepted Answer

Nitrogen fixation by bacteria is the primary natural method through which inert atmospheric nitrogen is converted into forms usable by plants, making it a critical and often limiting step in the nitrogen cycle for plant growth.

Question 8

-Which of the following is a source of human-fixed nitrogen?
I. industrially produced fertilizers
II. cultivation of soybeans
III. irrigation agriculture

Accepted Answer

Industrially produced fertilizers are a direct source of human-fixed nitrogen, as they often contain nitrogen compounds that are synthesized through processes like the Haber-Bosch process. The cultivation of soybeans, and other legumes, involves symbiotic relationships with nitrogen-fixing bacteria, which convert atmospheric nitrogen into forms usable by plants, thus increasing the nitrogen content of the soil through biological means. Irrigation agriculture does not inherently fix nitrogen; it is a method of water application to crops and does not directly contribute to nitrogen fixation.

Question 9

-Consider the global nitrogen cycle depicted in the accompanying figure. How are humans altering this cycle?

Accepted Answer

Humans alter the nitrogen cycle primarily through industrial nitrogen fixation, which increases the amount of reactive nitrogen in the environment.

Question 10

-Based on the experiment in the accompanying figure, which of the following are plausible reasons for the result?
I. No nutrients evaporate now that vegetation is absent.
II. Nutrients dissolve in the water running through the watershed.
III. Nutrients are attached to small particles of sand or clay that leave the watershed.
IV. Plant roots that held soil particles in place are no longer there.

Accepted Answer

II, III, and IV are plausible reasons for the result observed in the experiment. Nutrients can dissolve in water, be attached to particles that leave the watershed, and the absence of plant roots can lead to increased erosion, all contributing to nutrient loss. Nutrients do not evaporate, making option I implausible.

Question 11

-After looking at the experiment in the accompanying figure, what can be said about nutrient export in ecosystems? Nutrient export is ________.

Accepted Answer

Nutrient export is typically higher in a clear-cut watershed because the removal of vegetation reduces the uptake of nutrients by plants and increases runoff, leading to greater loss of nutrients from the ecosystem.

Question 12

Considering its total area covered, which ecosystem type represented in the figure has a very low level of economic impact on Earth's ecosystem, assuming that NPP is positively correlated with economic value?

Accepted Answer

The rock, sand, and ice ecosystem type has a low level of economic impact on Earth's ecosystem since it has negligible Net Primary Productivity (NPP) compared to other ecosystem types. NPP is positively correlated with economic value, and since there is little to no productivity in this ecosystem type, it has a low economic value.

Question 13

-Which of the following human activities is impacting the water cycle the LEAST?

Accepted Answer

Processing of salt water to freshwater (desalination) has a relatively minor impact on the global water cycle compared to the other options listed. While it does involve the removal of salt from seawater to produce freshwater, its scale and impact on the overall water cycle are less significant compared to the extensive changes in land use and water consumption associated with increased asphalt and concrete surfaces, conversion of natural landscapes into agricultural fields, and the expansion of irrigated agriculture. These activities alter evaporation rates, groundwater recharge, and runoff patterns on a much larger scale.

Question 14

-Which category in the figure makes available the highest productivity per square meter?

Accepted Answer

Algal beds and reefs have the highest productivity per square meter among the options given. This is because they are rich in nutrients and light, which are essential for photosynthesis, leading to high primary productivity.

Question 15

Which of the following most often controls the rate of nutrient cycling in ecosystems?

Accepted Answer

The rate of decomposition of detritus (dead plant and animal matter) is what most often controls the rate of nutrient cycling in ecosystems. This is because decomposers (such as bacteria and fungi) break down the detritus and release the nutrients back into the ecosystem for use by other organisms. Primary and secondary productivity can affect the amount of detritus present, but they do not directly control the rate of nutrient cycling.

Question 16

Regarding soil and organic matter in humus, which of the following statements is TRUE?

Accepted Answer

Completely decayed soil organic matter is called humus, and it contains both organic and inorganic nutrients. Over time, the organic nutrients in humus will be further broken down and converted into inorganic nutrients by microorganisms, making them available for plant uptake. Therefore, option A and B are not accurate, and option D is only partially correct as it describes the fate of organic nutrients in soil organic matter but does not account for the inorganic nutrients present in humus.

Question 17

- Consider the global water cycle depicted in the accompanying figure. Which one of the reserves contains the smallest percentage of global water?

Accepted Answer

The answer of 
- Consider the global water cycle depicted...

Question 18

Which statement best describes what ultimately happens to the chemical energy that is NOT converted to new biomass in the process of energy transfer between trophic levels in an ecosystem?

Accepted Answer

The energy not converted to biomass is lost as heat or eliminated as waste, aligning with the second law of thermodynamics, which states that energy transformations are not 100% efficient and some energy is always lost as heat to the surroundings.

Question 19

-Which habitat types in the accompanying figure cover the largest area?

Accepted Answer

Open ocean covers the largest area compared to the other options listed. It encompasses the majority of the Earth's water surface, far exceeding the combined area of coastal zones, reefs, wetlands, and tropical forests.

Question 20

-Which habitat type in the figure makes available the most new tissue to consumers?

Accepted Answer

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Quiz 53: Ecosystems and Global Ecology