Ecosystems: Energy and Nutrient Flow Module

Which of these biomes generally lies between tundra and temperate broadleaf forest?

Coniferous forest. The northern coniferous forest, or taiga, is the largest terrestrial biome on Earth, stretching in a broad band across North America and Asia south of the Arctic Circle. Taiga is also found at cool, high elevations in more temperate latitudes, such as much of the mountainous region of western North America. Temperate broadleaf forests grow throughout midlatitude regions. Tundra covers expansive areas of the Arctic between the taiga and polar ice.

Why is a diagram of energy flow from trophic level to trophic level shaped like a pyramid?

Most energy at each level is lost, leaving little energy for the next level. When energy flows as organic matter through the trophic levels of an ecosystem, much of it is lost at each link in a food chain. A pyramid of production illustrates the cumulative loss of energy with each transfer in a food chain. In an idealized pyramid, 10% of the energy available at each trophic level becomes incorporated into the next higher level. The efficiencies of energy transfer usually range from 5% to 20%. In other words, 80-95% of the energy at one trophic level never transfers to the next level.

Which of the following is not an abiotic factor that shapes ecosystems?

Predators. The biotic environment includes what an animal eats and any predators that threaten the animal. Soil structure, pH, and nutrient content often play major roles in determining the distribution of plants. On land, wind is often an important abiotic factor. Wind increases an organism's rate of water loss by evaporation. In some ecosystems, fire occurs frequently enough that many plants have adapted to this challenging circumstance. Water is essential to all life. Thus, for terrestrial organisms, drying out in the air is a major danger.

Which of the following is dominated by plants that drop their leaves in the winter to conserve water?

Temperate broadleaf forest. Temperate broadleaf forests grow throughout midlatitude regions, where there is sufficient moisture to support the growth of large trees. These forests typically have a growing season of five to six months and a distinct annual rhythm. Trees drop their leaves and become dormant in late autumn, preventing the loss of water from the tree at a time when frozen soil makes water less available. The trees produce new leaves in the spring. Deserts and savannas have few trees, and they conserve water in different ways. Coniferous forests and tropical rain forests have trees that drop their leaves slowly year-round, not all at once, to conserve water.

Which of the following occurs in areas too warm for coniferous forest and too dry for temperate forest?

Temperate grassland.Temperate grasslands have some characters of tropical savannas, but they are mostly treeless, except along rivers or streams, and are found in regions of relatively cold winter temperatures. Precipitation—averaging between 25 and 75 cm per year and with periodic severe droughts—is too low to support forest growth. Coniferous forests are found at cool, high elevations in more temperate latitudes.

The energy for nearly every organism in nearly every ecosystem ultimately comes from __________.

The Sun. All organisms require a source of energy to live. Solar energy from sunlight, captured during the process of photosynthesis, powers most ecosystems. Food, respiration, and decomposition could not exist without the Sun. Minerals in the soil are essential to life, but they do not provide the energy for photosynthesis.

Which of the following would be relevant only to the largest lakes?

The aphotic zone. Below the photic zone of the ocean lies the aphotic zone. Although there is not enough light for photosynthesis between 200 and 1,000 m, some light does reach these depths. This dimly lit world, sometimes called the twilight zone, is dominated by a fascinating variety of small fishes and crustaceans. Only the very largest and deepest lakes have an aphotic zone. The benthic realm is the floor of a body of water. Zooplankton are small, drifting animals. Phytoplankton are microscopic algae and cyanobacteria. The depth of light penetration, a maximum of 200 m, marks the photic zone. Even small lakes have a photic zone.

The tundra biome gets little precipitation, but during the short summer season, it is very wet, with many marshy areas, ponds, and bogs. Why?

Water cannot soak into the frozen ground. The arctic tundra is characterized by permafrost, continuously frozen subsoil—only the upper part of the soil thaws in summer. The arctic tundra may receive as little precipitation as some deserts. But poor drainage, due to the permafrost, and slow evaporation keep the soil continuously saturated.

Which of the following lists only abiotic environmental factors?

Wind, temperature, soil minerals, light. Abiotic factors are the environment's nonliving component, the physical and chemical factors such as temperature, forms of energy available, water, and nutrients. Biotic factors, which include all of the organisms in the area, are the living component of the environment.

Which of the following would you expect to find in a rain shadow?

a dessert. At higher latitudes, large deserts may exist in the rain shadows of mountains; these encompass much of central Asia east of the Caucasus Mountains and much of Washington State and Oregon east of the Cascade Mountains. The Mojave Desert, along with much of the rest of Southern California and Nevada, are in the rain shadow of the Sierra Nevada. Rain forests exist in equatorial areas where the temperature is warm and days are 11-12 hours long year-round. Tundra covers expansive areas of the Arctic between the taiga and polar ice.

An ecosystem is unlikely to be limited by the supply of __________ because it can be obtained from the air.

carbon. Carbon, the major ingredient of all organic molecules, has an atmospheric reservoir and cycles globally. On a global scale, the return of CO2 to the atmosphere by cellular respiration closely balances its removal by photosynthesis. Water, phosphorus, calcium, and nitrogen are obtained from the soil.

Which of the following describes the climatic conditions characteristic of the coniferous forest?

cold and snowy. The coniferous forest is characterized by long, cold winters and short, wet summers, which are sometimes warm. Most of the precipitation is in the form of snow. The conical shape of many conifers prevents too much snow from accumulating on their branches and breaking them.

In an ecosystem, the __________ is always greater than the __________.

energy used by primary consumers . . . energy used by secondary consumers. An important implication of the stepwise decline of energy in a trophic structure is that the amount of energy available to top-level consumers is small compared to the amount of energy available to lower-level consumers. Only a tiny fraction of the energy stored by photosynthesis flows through a food chain all the way to a tertiary consumer. This explains why top-level consumers require so much geographic territory: It takes a lot of vegetation to support trophic levels that are so many steps removed from photosynthetic production. Ecologists call the amount, or mass, of living organic material in an ecosystem the biomass.

Surface winds tend to blow toward the equator because __________.

equatorial air is heated by the Sun and rises. Heated by the direct rays of the Sun, moist air at the equator rises, creating an area of calm or very light winds known as the doldrums. As warm equatorial air rises, it cools and releases much of its water content. After losing their moisture over equatorial zones, high-altitude air masses spread away from the equator until they cool and descend again at latitudes of about 30° north and south.

The primary ecological factor determining the distribution of deserts is __________.

moisture. The primary ecological factor determining the distribution of deserts is moisture. Deserts are the driest of all terrestrial biomes, characterized by low and unpredictable rainfall. Large tracts of desert occur in two regions of descending dry air centered around the 30° north and south latitudes. At higher latitudes, large deserts may occur in the rain shadows of mountains.

Most plants get nitrogen from __________.

nitrates in the soil. The distribution and abundance of photosynthetic organisms, including plants, algae, and photosynthetic bacteria, depend on the availability of inorganic nutrients such as nitrogen and phosphorus. Plants obtain these nutrients from the soil. Soil structure, pH, and nutrient content often play major roles in determining the distribution of plants. Nitrogen has two abiotic reservoirs, the atmosphere and the soil. The atmospheric reservoir is huge; almost 80% of the atmosphere is nitrogen gas (N2). However, plants cannot absorb nitrogen in the form of N2.

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. The Sun supplies ecosystems with a continual influx of energy, but aside from an occasional meteorite, there are no extraterrestrial sources of chemical elements. Life, therefore, depends on the recycling of chemicals. Organisms must have both energy and nutrients to live.

The kind of tropical forest in a given area—thorn forest, deciduous forest, or rain forest—depends mostly on __________.

rainfall. Tropical forests occur in equatorial areas where the temperature is warm and the days are 11-12 hours long year-round. Rainfall in these areas is quite variable, and this variability, rather than temperature or day length, generally determines the vegetation that grows in a particular tropical forest. Frequent fires are a typical part of savannas and temperate grasslands, not tropical forests.

Most __________ must live in both the benthic realm and the photic zone.

seaweeds. Most seaweeds must live in both the benthic realm and the photic zone. The depth of light penetration, a maximum of 200 m, marks the photic zone. In shallow areas such as the submerged parts of continents, the photic zone includes both the pelagic and the benthic realms. In these sunlit regions, photosynthesis by phytoplankton and multicellular algae provides energy and organic carbon for a diverse community of animals.

Which of the following might eat phytoplankton?

shrimp. Phytoplankton are microscopic algae and cyanobacteria that live in the pelagic realm of the photic zone. The photic zone is a shallow, sunlit region of the ocean. Shrimp would be most likely to eat phytoplankton because they live in the same region as phytoplankton. Sharks must feed on prey larger than phytoplankton, such as large fish or sometimes whales. Beavers are found near fresh water, not the ocean. Seals and seagulls eat a variety of prey larger than phytoplankton, such as fish, squid, and crabs.

An ecologist studying how cattle grazing affects the population dynamics of native animals like pronghorns and prairie dogs is focusing on __________.

the community. The community is an assemblage of all the populations of organisms living close enough together for potential interaction—all of the biotic factors in the environment. An ecologist working at this level might focus on interspecies interactions. The population is a group of individuals of the same species living in a particular geographic area. Biomes are the major types of ecological associations that occupy broad geographic regions of land or water. The ecosystem includes both the biotic and the abiotic components of the environment. At the organism level, ecologists may examine how one kind of organism meets the challenges and opportunities of its environment through its physiology or behavior.

In a forest, bacteria are especially important in __________.

the nitrogen cycle. Nitrogen has two abiotic reservoirs, the atmosphere and the soil. The atmospheric reservoir is huge; almost 80% of the atmosphere is nitrogen gas (N2). However, plants cannot absorb nitrogen in the form of N2. The process of nitrogen fixation, which is performed by some bacteria, converts N2 to compounds of nitrogen that can be used by plants. Without these organisms, the natural reservoir of usable soil nitrogen would be extremely limited. In a forest, trees perform photosynthesis. Ecological succession is when a disturbed area is colonized by a variety of species, which are gradually replaced by a succession of other species. The phosphorus cycle depends on the weathering of rock. Recycling of energy is dominated by decomposers.

Change of seasons is caused by __________.

the tilt of the Earth. The seasons of the year result from the permanent tilt of the planet on its axis as it orbits the Sun. The globe's position relative to the Sun changes through the year. The Northern Hemisphere, for instance, is tipped most toward the Sun in June. The more direct angle and increased intensity of the Sun result in the long days of summer in that hemisphere. The combination of the prevailing winds, the planet's rotation, the unequal heating of surface waters, and the locations and shapes of the continents creates ocean currents, not the seasons.

"Brook trout prefer to live in cold, moving water, with high levels of oxygen, a gravel bottom, and abundant aquatic insects." This is a description of __________.

the trout's habitat. "Brook trout prefer to live in cold, moving water, with high levels of oxygen, a gravel bottom, and abundant aquatic insects." This is a description of the trout's habitat. An organism's habitat, the specific environment it lives in, includes the biotic and abiotic factors present in its surroundings. Biomes are the major types of ecological associations that occupy broad geographic regions of land or water. The community is an assemblage of all the populations of organisms living close enough together for potential interaction. The description includes living and nonliving aspects, so both biotic and abiotic factors are part of the trout's habitat.

An organism's "trophic level" refers to __________.

what it eats. An organism's "trophic level" refers to what it eats. A trophic level is each of several hierarchical levels in an ecosystem, comprising organisms that share the same function in the food chain and the same nutritional relationship to the primary sources of energy. The specific environment an animal lives in is its habitat.