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The biggest difference between the flow of energy and the flow of chemical nutrients in an ecosystem is that __________. |
nutrients are recycled, but energy is not |
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The biggest difference between the flow of energy and the flow of chemical nutrients in an ecosystem is that nutrients are recycled, but energy is not. Chemical nutrients can be recycled within ecosystems through biogeochemical cycles. Energy is lost from an ecosystem as a result of respiration. It is incorrect to say that the biggest difference between the flow of energy and the flow of chemical nutrients in an ecosystem is that the amount of energy is much greater than the amount of nutrients. Energy and nutrients are not directly comparable in this fashion. It is incorrect to say that the biggest difference between the flow of energy and the flow of chemical nutrients in an ecosystem is that energy is recycled, but nutrients are not. It is incorrect to say that the biggest difference between the flow of energy and the flow of chemical nutrients in an ecosystem is that organisms always need nutrients but they don’t always need energy, or that organisms always need energy but they don’t always need nutrients. Organisms always need both. |
… |
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Primary producers are _________. |
autotrophs |
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Primary producers are autotrophs. Ecologists group species into trophic levels based on species’ main sources of nutrition and energy. The trophic level that ultimately supports all the other levels consists of autotrophs, also called the primary producers of the ecosystem. Most autotrophs are photosynthetic organisms that use light energy to synthesize sugars and other organic compounds, which they use as fuel for cellular respiration and as building materials for growth. The most common autotrophs are plants, algae, and photosynthetic prokaryotes, although chemosynthetic prokaryotes are the primary producers in ecosystems such as deep-sea hydrothermal vents and places deep below the ground or ice. Organisms in trophic levels above the primary producers are heterotrophs, which depend directly or indirectly on the outputs of primary producers for their sources of energy. Herbivores, which eat plants and other primary producers, are primary consumers. Carnivores that eat herbivores are secondary consumers, and carnivores that eat other carnivores are tertiary consumers. "Grain farmers" is incorrect because these farmers plant grains, which are organisms that are autotrophs. "Grazers" is incorrect because grazers are herbivores or consumers that eat the primary producers. "Detritivores" is incorrect because they are consumers that derive their energy and nutrients from nonliving organic material such as corpses, fallen plant material, and the wastes of living organisms. |
… |
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Biological augmentation is a process that _________. |
uses organisms to add essential materials to a degraded ecosystem |
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Biological augmentation is a process that uses organisms to add essential materials to a degraded ecosystem. This is in contrast to bioremediation, which is a strategy for removing harmful substances from an ecosystem. To augment ecosystem processes, restoration ecologists need to determine which factors, such as chemical nutrients, have been lost from a system and are limiting the system’s recovery. Encouraging the growth of plants that thrive in nutrient-poor soils often speeds up succession and ecosystem recovery. For example, in alpine ecosystems of the western United States, nitrogen-fixing plants such as lupines are often planted to increase nitrogen concentrations in soils disturbed by mining and other human activities. Once these nitrogen-fixing plants become established, other, native species are better able to obtain enough soil nitrogen to survive. In systems where the soil has been severely disturbed or where topsoil is missing entirely, plant roots may lack the mycorrhizal symbionts that help them meet their nutritional needs. Ecologists restoring a tallgrass prairie in Minnesota recognized this deficiency and enhanced the recovery of native species by adding the mycorrhizal symbionts to the soil they seeded. Restoring the physical structure and plant community of an ecosystem does not always ensure that animal species will recolonize a site and persist there, however. Because animals provide critical ecosystem services, including pollination and seed dispersal, restoration ecologists sometimes help wildlife reach and use restored ecosystems. They might, for instance, release animals at a site or establish habitat corridors that connect a restored site to places where the animals are now found. They sometimes establish artificial perches for birds to use at a site. These and other efforts can increase the biodiversity of restored ecosystems and help the community persist. The long-term objective of restoration is to return an ecosystem to its predisturbance state as much as possible. The figure below identifies several ambitious and successful restoration projects taking place around the world. The large number of such projects and the dedication of the people engaged in them suggest that restoration ecology will continue to grow as a discipline for many years. "Uses organisms to help remove minerals from an ecosystem" is incorrect because this describes biological augmentation, a process that uses organisms to add essential materials to a degraded ecosystem. "Uses organisms to add essential materials to a thriving ecosystem" is incorrect because thriving ecosystems do not need to be biologically augmented. |
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An example of restoration ecology is ________. |
restoring seaweed and seagrass beds of fish and shellfish nurseries |
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An example of restoration ecology is restoring seaweed and seagrass beds of fish and shellfish nurseries. Restoring the physical structure and plant community of an ecosystem does not always ensure that animal species will recolonize a site and persist there. Because animals provide critical ecosystem services, including pollination and seed dispersal, restoration ecologists sometimes help wildlife reach and use restored ecosystems. They might, for instance, release animals at a site or establish habitat corridors that connect a restored site to places where the animals are now found. They sometimes establish artificial perches for birds to use at a site. These and other efforts can increase the biodiversity of restored ecosystems and help the community persist. The long-term objective of restoration is to return an ecosystem to its predisturbance state as much as possible. The map below identifies several ambitious and successful restoration projects taking place around the world. The large number of such projects and the dedication of the people engaged in them suggest that restoration ecology will continue to grow as a discipline for many years. |
… |
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A measure of the total biomass accumulation during a given period of time is called the _________. |
net ecosystem production |
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A measure of the total biomass accumulation during a given period of time is called the net ecosystem production. Net ecosystem production, or NEP, is defined as gross primary production (GPP) minus the total respiration of all organisms in the system (RT)—not just that of primary producers, as for the calculation of NPP, but that of decomposers and other heterotrophs as well: NEP is useful to ecologists because its value determines whether an ecosystem is gaining or losing carbon over time. A forest may have a positive NPP but still lose carbon if heterotrophs release it as CO2 more quickly than primary producers incorporate it into organic compounds. In 2008, scientists measured NEP in the Pacific Ocean using high-resolution oxygen sensors. As the floats drifted with the current, they repeatedly moved between the ocean surface and a depth of 1,000 m, recording the O2 concentration in the water as they ascended. The researchers estimated an average NEP of 25 g C/(m2 · yr) over the three-year study, suggesting that phytoplankton in extensive regions of the oceans are more productive than previously thought. Studies like this are giving ecologists a new understanding of Earth’s carbon cycle and marine production. |
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"Net primary production" is incorrect because net primary production (NPP) is the gross primary production of an ecosystem minus the energy used by the producers for respiration. "Gross primary production" is incorrect because gross primary production (GPP) is the total primary production of an ecosystem. "Production efficiency" is incorrect because this is the percentage of energy stored in assimilated food that is not used for respiration or eliminated as waste. "Trophic efficiency" is incorrect because this is the percentage of production transferred from one trophic level to the next-higher trophic level. |
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Important biogeochemical cycles in ecosystems include all of the following except the ________ cycle. |
potassium |
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Important biogeochemical cycles in ecosystems do not include the potassium cycle. The figures seen here examine each of the major reservoirs of water, carbon, nitrogen, and phosphorus and the processes that drive each cycle. The widths of the arrows in the diagram approximately indicate the relative contribution of each process to the movement of water or a nutrient in the biosphere. The biological importance of each cycle is as follows: Water is essential to all organisms, and its availability influences the rates of ecosystem processes, particularly primary production and decomposition in terrestrial ecosystems. Carbon forms the framework of the organic molecules essential to all organisms. Organisms require phosphorus because it is a major constituent of nucleic acids, phospholipids, and ATP and other energy-storing molecules and is a mineral constituent of bones and teeth. Nitrogen is part of amino acids, proteins, and nucleic acids and is often a limiting plant nutrient. |
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A measure of production that is calculated by subtracting autotrophic respiration from all primary production in an ecosystem is called _________. |
net primary production |
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A measure of production that is calculated by subtracting autotrophic respiration from all primary production in an ecosystem is called net primary production. Net primary production (NPP) can be expressed as energy per unit area per unit of time [J/(m2 · yr)] or as biomass (mass of vegetation) added per unit area per unit of time [g/(m2 · yr)]. (Note that biomass is usually expressed in terms of the dry mass of organic material.) An ecosystem’s NPP should not be confused with the total biomass of photosynthetic autotrophs present, a measure called the standing crop. The net primary production is the amount of new biomass added in a given period of time. Although a forest has a large standing crop, its NPP may actually be less than that of some grasslands; grasslands do not accumulate as much biomass as forests do because animals consume the plants rapidly and because grasses and herbs decompose more quickly than trees do. Satellites are a powerful tool for studying global patterns of primary production. Images produced from satellite data show that different ecosystems vary considerably in their NPP. Tropical rain forests are among the most productive terrestrial ecosystems and contribute a large portion of the planet’s NPP. Estuaries and coral reefs also have very high NPP, but their contributions to the global total are smaller because these ecosystems cover only about one-tenth the area covered by tropical rain forests. In contrast, although the open oceans are relatively unproductive, their vast sizes mean that together, they contribute as much global NPP as terrestrial systems do. "Gross primary production" is incorrect because gross primary production (GPP) is the total primary production of an ecosystem. "Production efficiency" is incorrect because this is the percentage of energy stored in assimilated food that is not used for respiration or eliminated as waste. "Trophic efficiency" is incorrect because this is the percentage of production transferred from one trophic level to the next-higher trophic level. |
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The amount of chemical energy in a consumer’s food that is converted to its own new biomass over a period of time is called __________. |
secondary production |
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The amount of chemical energy in a consumer’s food that is converted to its own new biomass over a period of time is called secondary production. After a consumer feeds, only a portion of the food it consumes is converted to the organism’s own biomass. Primary production refers to the new biomass created in primary producers. Production efficiency refers to the fraction of food energy that is not used for respiration. Net ecosystem production refers to the total amount of biomass accumulated in a given time. It is incorrect to say that this question cannot be answered without knowing at which trophic level the organism feeds; it can be answered without this information. |
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The percentage of production transferred from one trophic level to the next-higher level is called ________. |
trophic efficiency |
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The percentage of production transferred from one trophic level to the next-higher level is called trophic efficiency. Trophic efficiencies must always be less than production efficiencies because the former take into account not only the energy lost through respiration and contained in feces but also the energy in organic material in a lower trophic level that is not consumed by the next-higher trophic level. Trophic efficiencies are generally only about 10% and range from approximately 5% to 20% in different ecosystems. In other words, 90% of the energy available at one trophic level typically is not transferred to the next-higher trophic level. This loss is multiplied over the length of a food chain: If 10% of available energy is transferred from primary producers to primary consumers (such as caterpillars) and 10% of that energy is transferred to secondary consumers (carnivores), then only 1% (10% of 10%) of net primary production is available to secondary consumers. "Net primary production" is incorrect because net primary production (NPP) is the gross primary production of an ecosystem minus the energy used by the producers for respiration. "Net ecosystem production" is incorrect because net ecosystem production (NEP) is the measure of total biomass accumulation during a given period of time. "Gross primary production" is incorrect because gross primary production (GPP) is the total primary production of an ecosystem. |
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Eutrophication in lakes is frequently the direct result of __________. |
nutrient enrichment such as nitrate and phosphate runoffs from land |
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Eutrophication in lakes is frequently the direct result of nutrient enrichment such as nitrate and phosphate runoffs from land. Sewage and factory wastes, runoffs of animal waste from pastures and stockyards, and the leaching of fertilizer from agricultural, recreational, and urban areas have overloaded many streams, lakes, and rivers with inorganic nutrients. This enrichment can result in an explosive increase in the density of photosynthetic organisms. Industrial poisons would most likely kill algae, not promote their growth. An increase in primary consumers might decrease, rather than increase, algal levels. |
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In a working ecosystem such as the arctic tundra, all of the following exist except _______. |
a reduction in the competition for resources |
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In a working ecosystem such as the arctic tundra, a reduction in the competition for resources does not exist. Instead, individuals compete to acquire the same limited resources. Populations change in size through births and deaths and through immigration and emigration. Primary producers convert the energy in sunlight to chemical energy through photosynthesis. Growth is often limited by abiotic factors such as low temperatures, scarce soil nutrients, and lack of light in winter. In addition, chemical elements such as carbon and nitrogen move in cycles between the physical environment and organisms. |
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Deforestation of a watershed _______. |
dramatically increases the flow of water and minerals out of the watershed |
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Deforestation of a watershed dramatically increases the flow of water and minerals out of the watershed. Experimental deforestation of a watershed dramatically increased the flow of water and minerals out of the watershed. Over three years, water runoff from the newly deforested watershed was 30-40% greater than that in a control watershed, apparently because there were no plants to absorb and transpire water from the soil. Most remarkable was the loss of nitrate, whose concentration in the creek increased 60-fold, reaching levels considered unsafe for drinking. The Hubbard Brook deforestation study showed that the amount of nutrients leaving an intact forest ecosystem is controlled mainly by the plants. Retaining nutrients in ecosystems thus helps to maintain the productivity of the systems and avoid problems such as algal "blooms" caused by excess nutrient runoff. "Dramatically increases the number of organisms in the watershed" and "helps with nutrient recycling" are incorrect because after deforestation, there are no plants to absorb and transpire water from the soil. "Prevents massive forest fires" is incorrect because the clear-cut study was done to study nutrient cycling in an ecosystem. |
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The main decomposers in an ecosystem are __________. |
fungi and prokaryotes |
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The main decomposers in an ecosystem are fungi and prokaryotes. These groups are most involved in the conversion of organic compounds to inorganic nutrients. |
… |
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The phosphorus cycle lacks a(n) __________ component. |
atmospheric |
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The phosphorus cycle lacks an atmospheric component. Gaseous phosphorus is insignificant. The other answer choices are incorrect. Living organisms are a part of the phosphorus cycle. The inorganic form of phosphorus (PO43-) is the form absorbed by plants. Phosphorus is found in water. |
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Which of the following statements is true? |
Over oceans, evaporation exceeds precipitation. |
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In an ecosystem, all incoming energy will eventually be __________. |
dissipated into space as heat |
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In an ecosystem, all incoming energy will eventually be dissipated into space as heat. Solar radiation is the ultimate energy source for most ecosystems, and respiratory heat loss is the ultimate sink. Photosynthesis and energy transfers are not 100-percent efficient. |
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Bioremediation is a process that _________. |
uses organisms to detoxify polluted ecosystems |
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Bioremediation is a process that uses organisms to detoxify polluted ecosystems. Some plants and lichens adapted to soils containing heavy metals can accumulate high concentrations of toxic metals such as lead and cadmium in their tissues. Restoration ecologists can introduce species such as prokaryotes, fungi, or plants to sites polluted by mining and other human activities and then harvest these species to remove the metals from the ecosystem. For instance, researchers in the United Kingdom have discovered a lichen species that grows on soil polluted with uranium dust left over from mining. The lichen concentrates uranium into a dark pigment, making the lichen useful as a biological monitor and potentially as a remediator. Ecologists already make use of the abilities of many prokaryotes to carry out bioremediation of soils and water. For example, scientists have sequenced the genomes of at least ten prokaryotic species specifically for their bioremediation potentials. One of the species, the bacterium Shewanella oneidensis, appears particularly promising because it can metabolize a dozen or more elements under aerobic and anaerobic conditions. In doing so, it converts soluble forms of uranium, chromium, and nitrogen to insoluble forms that are less likely to leach into streams or groundwater. Researchers at Oak Ridge National Laboratory in Tennessee stimulated the growth of Shewanella and other uranium-reducing bacteria by adding ethanol to groundwater contaminated with uranium because the bacteria can use ethanol as an energy source. In just five months, the concentration of soluble uranium in the ecosystem dropped by 80%. "Uses organisms to recolonize an ecosystem" is incorrect because bioremediation uses organisms to detoxify polluted ecosystems. "Uses organisms to add essential materials to a degraded ecosystem" is incorrect because this is biological augmentation. "Uses organisms to add essential materials to a thriving ecosystem" is incorrect because thriving ecosystems do not need to be bioremediated. |
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Which of the following is an ecosystem? |
All of the organisms living in your aquarium and the abiotic factors with which they interact |
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Of the choices listed, all of the organisms living in your aquarium and the abiotic factors with which they interact is an example of an ecosystem. All of the angelfish in your aquarium describe a population. All of the organisms living in your aquarium describe a community. All of the angelfish on the planet comprise a species, or perhaps a genus. Finally, the water, temperature, rocks, and other abiotic components of the aquarium do not represent an ecosystem, because ecosystems are composed of both abiotic factors and the organisms living in the environment. |
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Detritivores are _________. |
heterotrophs |
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Detritivores are heterotrophs. Detritivores and decomposers are terms used synonymously in this text to refer to consumers that derive their energy from detritus, which is nonliving organic material such as the remains of dead organisms, feces, fallen leaves, and wood. "Omnivores" is incorrect because omnivores are animals that regularly eat other animals as well as plants or algae. "Net secondary producers" is incorrect because net secondary production is energy stored in biomass represented by growth and reproduction. |
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It is true to say that over oceans, evaporation exceeds precipitation. Runoff and groundwater that flow to the oceans are responsible for balancing the water lost by evaporation. Over land, evaporation does not exceed transpiration and precipitation and water gain by precipitation exceeds water loss by evaporation and transpiration. Transpiration is evaporative water loss from terrestrial plants. Finally, only a small proportion of Earth’s water is found in living systems. |
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How do iron levels affect phytoplankton populations in a marine ecosystem? |
Iron stimulates the growth of cyanobacteria, which convert atmospheric N2 to nitrogenous minerals, stimulating the growth of phytoplankton. |
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In marine ecosystems, iron stimulates the growth of cyanobacteria, which convert atmospheric N2 to nitrogenous minerals, thus stimulating the growth of phytoplankton. This explains why marine waters lacking iron are very clear. Without cyanobacteria to convert nitrogen to usable forms, phytoplankton populations are likely to be low. Iron stimulates, rather than halts, the growth of cyanobacteria, leading to an increased phytoplankton population. Finally, nitrogen—not phosphorus—is generally the limiting nutrient in marine ecosystems. |
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A measure of the total primary production in an ecosystem is called the _________. |
gross primary production |
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A measure of the total primary production in an ecosystem is called the gross primary production. Total primary production in an ecosystem is known as that ecosystem’s gross primary production (GPP)—the amount of energy from light (or chemicals, in chemoautotrophic systems) converted to the chemical energy of organic molecules per unit of time. Not all of this production is stored as organic material in the primary producers because they use some of the molecules as fuel in their own cellular respiration. "Net ecosystem production" is incorrect because net ecosystem production (NEP) is the measure of total biomass accumulation during a given period of time. "Net primary production" is incorrect because the net primary production (NPP) is the gross primary production of an ecosystem minus the energy used by the producers for respiration. "Production efficiency" is incorrect because this is the percentage of energy stored in assimilated food that is not used for respiration or eliminated as waste. "Trophic efficiency" is incorrect because this is the percentage of production transferred from one trophic level to the next-higher trophic level. |
… |
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Bioremediation is a process that uses organisms to detoxify polluted ecosystems. Some plants and lichens adapted to soils containing heavy metals can accumulate high concentrations of toxic metals such as lead and cadmium in their tissues. Restoration ecologists can introduce species such as prokaryotes, fungi, or plants to sites polluted by mining and other human activities and then harvest these species to remove the metals from the ecosystem. For instance, researchers in the United Kingdom have discovered a lichen species that grows on soil polluted with uranium dust left over from mining. The lichen concentrates uranium into a dark pigment, making the lichen useful as a biological monitor and potentially as a remediator. Ecologists already make use of the abilities of many prokaryotes to carry out bioremediation of soils and water. For example, scientists have sequenced the genomes of at least ten prokaryotic species specifically for their bioremediation potentials. One of the species, the bacterium Shewanella oneidensis, appears particularly promising because it can metabolize a dozen or more elements under aerobic and anaerobic conditions. In doing so, it converts soluble forms of uranium, chromium, and nitrogen to insoluble forms that are less likely to leach into streams or groundwater. Researchers at Oak Ridge National Laboratory in Tennessee stimulated the growth of Shewanella and other uranium-reducing bacteria by adding ethanol to groundwater contaminated with uranium because the bacteria can use ethanol as an energy source. In just five months, the concentration of soluble uranium in the ecosystem dropped by 80%. "Uses organisms to add essential materials to a degraded ecosystem" is incorrect because this is biological augmentation. "Uses organisms to add essential materials to a thriving ecosystem" is incorrect because thriving ecosystems do not need to be bioremediated. |
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The direct product of nitrogen fixation is __________. |
NH3 |
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The direct product of nitrogen fixation is NH3. Ammonia is produced by nitrogen fixation. However, in the soil it is usually converted to ammonium (NH4+) before being taken up by plants. NH4 is a form of nitrogen that plants can use, but it is not a direct product of nitrogen fixation. The process of nitrification produces nitrite. Nitrite is converted to nitrate (NO3-) by nitrifying bacteria. Nitrogen fixation is a process that makes N2 available to plants. |
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The global hydrologic cycle supports a net flow of atmospheric water vapor __________. |
from the oceans to land |
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The global hydrologic cycle supports a net flow of atmospheric water vapor from the oceans to land. In other words, a net movement of water vapor is formed by evaporation from the sea to the land. The oceans contain more water than land does. Evapotranspiration, the release of water to the atmosphere, is higher in forested than in unforested biomes. Finally, tropical and polar regions do not best relate to the global hydrologic cycle in terms of movement of water. |
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Increased rates of decomposition occur in ________ ecosystems. |
tropical |
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Increased rates of decomposition occur in tropical ecosystems. Decomposition is controlled by the same factors that limit primary production in aquatic and terrestrial ecosystems. These factors include temperature, moisture, and nutrient availability. Decomposers usually grow faster and decompose material more quickly in warmer ecosystems. In tropical rain forests, most organic material decomposes in a few months to a few years, whereas in temperate forests, decomposition takes four to six years on average. The difference is largely the result of the higher temperatures and more abundant precipitation in tropical rain forests. |
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Most of the sunlight that reaches Earth __________. |
is not captured for use by living things |
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Most of the sunlight that reaches Earth is not captured for use by living things. Most solar radiation that reaches Earth’s surface lands on bare ground and bodies of water that absorb or reflect the incoming energy. |
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A study of metabolic rates in a terrestrial community showed that the energy released by respiration exceeded the energy captured in photosynthesis. Which of the following situations is most likely? |
Community biomass is decreasing. |
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A study of metabolic rates in a terrestrial community showed that the energy released by respiration exceeded the energy captured in photosynthesis. Based on the scenario, community biomass is decreasing. Net primary productivity is the difference between the yield of photosynthesis and the consumption of organic fuel in respiration. Primary productivity can be expressed as the biomass of vegetation added to an area of the ecosystem per unit of time. If the energy released by respiration exceeds the energy captured in photosynthesis, biomass decreases. The other answer choices are incorrect. Community biomass is not increasing. The laws of thermodynamics are in effect. Finally, it is incorrect to say that none of the listed responses is correct; one is correct. |
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The percentage of energy stored in assimilated food that is not used for respiration is the _________. |
production efficiency |
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The percentage of energy stored in assimilated food that is not used for respiration is the production efficiency. We can measure the efficiency of animals as energy transformers using the following equation: Production efficiency = Net secondary production × 100% Net secondary production is the energy stored in biomass represented by growth and reproduction. Assimilation consists of the total energy taken in minus the energy lost in feces or used for growth, reproduction, and respiration. For the caterpillar in the figure below, production efficiency is 33%; that is, 67 J of the 100 J of assimilated energy is used for respiration. (The 100 J of energy lost as undigested material in feces also does not count toward assimilation.) Birds and mammals typically have low production efficiencies, in the range of 1-3%, because they use so much energy to maintain a high body temperature. Fishes, which are mainly ectothermic, have production efficiencies around 10%. Insects and microorganisms are even more efficient, with production efficiencies averaging 40% or more. "Net primary production" is incorrect because net primary production (NPP) is the gross primary production of an ecosystem minus the energy used by the producers for respiration. "Net ecosystem production" is incorrect because net ecosystem production (NEP) is the measure of total biomass accumulation during a given period of time. "Gross primary production" is incorrect because gross primary production (GPP) is the total primary production of an ecosystem. |
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What is the main abiotic reservoir for elements involved in local biogeochemical cycles, such as calcium and phosphorus? |
Soil |
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The main abiotic reservoir for elements involved in local biogeochemical cycles, such as calcium and phosphorus, is soil. Soil is the main abiotic reservoir for these elements. Oceans, rivers, wind, and the atmosphere are not the main abiotic reservoirs for elements involved in local biogeochemical cycles; thus, these answer choices are incorrect. |
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Local conditions such as heavy rainfall or the removal of plants may limit the amount of nitrogen, phosphorus, or calcium available to a particular ecosystem, but the amount of carbon available to the system is seldom a problem. Why? |
Many nutrients come from the soil, but carbon comes from the air. |
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Local conditions such as heavy rainfall or the removal of plants may limit the amount of nitrogen, phosphorus, or calcium available to a particular ecosystem, but the amount of carbon available to the system is seldom a problem, because whereas many nutrients come from the soil, carbon comes from the air. So while nutrients in the soil are subject to runoff, atmospheric CO2 is not. Life on Earth is based on carbon. As an element, carbon cannot be manufactured. Plants do not acquire carbon from the soil. Finally, symbiotic bacteria play a major role in helping plants acquire nitrogen, not carbon. |
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The law of conservation of mass is important in ecology because _________. |
it allows scientists to determine the gain or loss of a chemical element in an ecosystem |
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The law of conservation of mass is important in ecology because it allows scientists to determine the gain or loss of a chemical element in an ecosystem. Matter, like energy, cannot be created or destroyed. This law of conservation of mass is as important for ecosystems as the laws of thermodynamics are. Because mass is conserved, we can determine how much of a chemical element cycles within an ecosystem or is gained or lost by that ecosystem over time. Unlike energy, chemical elements are continually recycled within ecosystems. For example, a carbon atom in CO2 is released from the soil by a decomposer, taken up by grass via photosynthesis, consumed by a grazing animal, and returned to the soil in the animal’s waste. Measurement and analysis of chemical cycling are important in ecosystem ecology. Although most elements are not gained or lost on a global scale, they can be gained by or lost from a particular ecosystem. In a forest, most mineral nutrients—the essential elements that plants obtain from soil—typically enter as dust or as solutes dissolved in rainwater or leached from rocks in the ground. Nitrogen is also supplied through the biological process of nitrogen fixation. In terms of losses, some elements return to the atmosphere as gases, and others are carried out of the ecosystem by moving water or wind. Like organisms, ecosystems are open systems, which absorb energy and mass and release heat and waste products. "It helps us understand how to reduce waste" is incorrect because mass is conserved, which means that scientists can determine how much of a chemical element cycles within an ecosystem or is gained or lost by that ecosystem over time. |
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Which of the following statements is supported by the trophic relationships shown in the diagram? |
Squids eat fishes. |
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Based on the food web diagram, label the following statements as true or false. |
Phytoplankton are primary consumers. False Squids are secondary consumers. True Squids are tertiary consumers. True Leopard seals are quaternary consumers. True |
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Which of the following groups can be quaternary consumers in this food web? |
sperm whales |
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The longest food chain in this food web includes nine groups of organisms. Which of the following groups is included in that food chain? |
birds |
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Which trophic levels do fishes occupy in this food web? |
secondary consumers tertiary consumers quaternary consumers |
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Five different baleen whale species are endangered and may go extinct. What would be the most likely effect of removing all baleen whales from this food web? |
The krill population would increase. |
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Suppose that humans increase their consumption of Antarctic fishes, causing a significant reduction in the size of fish populations. What would be the most likely effect of a reduction in the size of Antarctic fish populations? |
The carnivorous plankton population would increase. The elephant seal population would decrease. The sperm whale population would decrease. |
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An organism’s "trophic level" refers to _____. |
its food source |
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Use the following diagram of a hypothetical food web to answer the question. The arrows represent the transfer of energy between the various trophic levels. |
C |
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What do the bars on this graph represent? The solar energy available to each ecosystem as determined by its geographic location. |
The amount of solar energy converted to chemical energy in organic compounds for a given area per year. |
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What is represented by the distance between two vertical white gridlines on this graph? A 500-fold increase in net primary productivity |
500 g/m2/year |
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The net primary productivity of cultivated land is most similar to the net primary productivity of which ecosystem? Boreal forest (taiga) |
Boreal forest (taiga) Temperate grassland |
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The biomass of cultivated land approximately equals the biomass of temperate grassland. Supported |
Cannot be determined from this graph. |
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According to this graph, algal beds and coral reefs have the highest net primary productivity. Supported |
Supported |
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The net primary productivity of an estuary ecosystem is roughly 12 times the net primary productivity of the open ocean. Supported |
Supported |
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Identifying trophic levels in a food web |
Detritus dead animal rotting log Primary producer living maple leaves Primary consumer or decomposer maggots fungus cricket Secondary consumer earthworm millipede Tertiary consumer Both secondary and tertiary consumer robin alligator lizard |
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Calculating trophic efficiency |
14.9,10.6,12.0 % |
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Analyzing energy flow -Animals that produce their own body heat and maintain a high body temperature are likely to be less efficient at converting food into biomass than are animals that do not regulate their body temperature. |
-Animals that produce their own body heat and maintain a high body temperature are likely to be less efficient at converting food into biomass than are animals that do not regulate their body temperature. -If the lowest trophic level of an ecosystem–the primary producers–contains 1,200 grams of biomass per square meter, it is reasonable to expect the secondary consumer level to contain about 12 grams of biomass per square meter. -In a trophic pyramid, biomass represents chemical energy. -Energy used in the production of offspring is available to higher trophic levels. |
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What percentage of the solar energy that reaches the marsh is incorporated into gross primary production? |
5.8% The answer is the gross grass production divided by the solar radiation = 34,580 ÷ 600,000 = 0.058 or 5.8%. |
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What percentage of the solar energy that reaches the marsh is incorporated into net primary production? |
1.1% The answer is the net grass production divided by the solar radiation = 6,585 ÷ 600,000 = 0.011 or 1.1%. |
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How much energy is lost by primary producers as respiration in this ecosystem? |
27,995 kcal/(m2 • yr) The energy lost by primary producers as respiration is the gross grass production minus the net grass production = 34,580 kcal/(m2 • yr) – 6,585 kcal/(m2 • yr) = 27,995 kcal/(m2 • yr). |
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How much energy is lost as respiration by the insect population? |
224 kcal/(m2 • yr) The energy lost by insects as respiration is the gross insect production minus the net insect production = 305 kcal/(m2 • yr) – 81 kcal/(m2 • yr) = 224 kcal/(m2 • yr). |
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If all of the detritus leaving the marsh is plant material, what percentage of all net primary production leaves the marsh as detritus each year? |
56% The answer is the amount of energy in detritus leaving the marsh divided by the net grass production = 3,671 ÷ 6,585 = 0.56 or 56%. |
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The carbon cycle is one of many biogeochemical cycles on Earth. Can you identify the main features of a biogeochemical cycle and show how the carbon cycle exhibits these features? Drag the terms on the left to the appropriate blanks on the right to complete the sentences. Not all terms will be used. |
1. In a biogeochemical cycle, a chemical element spends time in different places, called reservoirs. 2. As a chemical element moves through a biogeochemical cycle, it moves between "bio" and "geo." The "bio" in biogeochemical refers to biotic reservoirs, or living organisms. 3. The "geo" in biogeochemical refers to Earth–specifically, to the abiotic reservoirs where a chemical element can be found. 4. In the terrestrial carbon cycle, the abiotic reservoir from which living organisms directly obtain their carbon is the atmosphere. 5. Carbon moves from an abiotic reservoir to living organisms during the process of photosynthesis. 6. Carbon moves from living organisms to an abiotic reservoir during the process of cellular respiration. |
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The carbon cycle describes the cycling of carbon between Earth’s biotic (living) and abiotic (nonliving) reservoirs. Identify the major reservoirs and processes in the carbon cycle by labeling the diagram below. Drag the labels to their appropriate locations on the diagram of the carbon cycle. |
A. CO2 in atmosphere B. Photosynthesis on land C. Photosynthesis in ocean D. Cellular respiration E. Plants F. Burning fossil fuels G. Consumers H. Decomposers |
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Which of the activities listed below could help limit global warming by slowing the increase in atmospheric carbon dioxide levels? limiting soil erosion so organic matter takes longer to decompose |
choosing a fuel-efficient car, or bicycling to school or work limiting soil erosion so organic matter takes longer to decompose replacing fossil fuels with nuclear energy |
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