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WORKSHEET: ECOSYSTEMS (KEY)

1. The Nature of EcosystemsA. Overview of the Participants

1. Regions on the earth function as systems running on energy from the sun processed through various organisms.2. Primary producers are autotrophs that can capture sunlight energy and incorporate it into organic compounds.3. Consumers are heterotrophs that feed on tissues of other organisms.

a. Herbivores eat plants.b. Carnivores eat animals.c. Parasites reside in or on living hosts and extract energy from them.d. Omnivores eat a variety of organisms.

4. Detritivores include small invertebrates that feed on partly decomposed particles of organic matter (detritus).5. Decomposers are also heterotrophs and include fungi and bacteria that extract energy from the remains or products of organisms.6. An ecosystem is a complex of organisms interacting with one another and with the physical environment.

a. Ecosystems are open systems through which energy flows and materials are cycled.b. Ecosystems require energy and nutrient input; they generate energy (usually as heat) and nutrient output.

B. Structure of Ecosystems1. Trophic (“feeding”) levels are a hierarchy of energy transfers, or bluntly stated, “Who eats whom?”

a. Level 1 (closest to the energy source) consists of producers; level 2 comprises herbivores; and levels 3 and above are carnivores.b. Decomposers feed on organisms from all levels.

2. Food chains cross-connect to form food webs.a. A sequence of who eats whom is called a food chain; for example, plant ——> cutworm ——> garter snake ——> sandpiper ——> marsh hawk.b. Interconnected food chains comprise food webs in which the same food resource is often part of more than one food chain.

2. The Nature of Food WebsA. How many energy transfers are there?

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1. Energy that producers initially capture passes through no more than four or five transfers.2. Energy is lost at each transfer.

B. There are two categories of food webs.1. Energy flows into ecosystems from the sun.

a. Energy flows through ecosystems by way of grazing food webs, in which energy flows from plants to herbivores and then to carnivores.b. In detrital food webs, it flows mainly from plants through decomposers and detritivores.

2. Energy leaves ecosystems through heat losses generated by metabolism.

3. DDT in Food WebsA. DDT, which was an effective chemical to kill mosquitoes, accumulates in fatty

tissues and results in biological magnification and unexpected nontarget effects.

B. Even though DDT has been banned since the 1970s, the chemical is very persistent in certain sections of the environment, namely sediments.

4. Studying Energy Flow Through EcosystemsA. What Is Primary Productivity?

1. Primary productivity is the rate at which producers get and store energy in their tissues.

a. Gross primary productivity is the total rate of photosynthesis for the ecosystem during a specified interval.b. Net ecosystem production is the energy left over after that which is used by the plants and soil organisms is subtracted from the gross primary production.

2. Many factors impact net production, including body size, mineral availability, temperature range, sunlight, and rainfall.

B. Ecological Pyramids1. Trophic structure can be diagrammed as a pyramid in which producers form a base for successive tiers of consumers above them.2. Pyramids can be of two basic types.

a. A biomass pyramid makes provision for differences in size of organisms by using the weight of the members in each trophic level.b. An energy pyramid reflects the trophic structure most accurately because it is based on energy losses at each level.

5. Energy Flow Through Silver SpringsA. To construct an energy pyramid for a freshwater spring, you must measure the

energy transfers in each organism and then multiply that by the population size.B. Only about 6 to 16 percent of the energy entering one level becomes available

to organisms at the next level.

6. Overview of Biogeochemical CyclesA. Biogeochemical cycles influence the availability of essential elements in

ecosystems.1. Elements are available to producers as ions.2. Nutrient reserves are maintained by environmental inputs and recycling activities.3. The amount of nutrients being cycled is greater than the amount entering or leaving.4. Environment inputs are by precipitation, metabolism, and weathering. Outputs are by runoff and evaporation.

B. There are three categories of biogeochemical cycles.1. In the hydrologic cycle, oxygen and hydrogen move as water molecules.

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2. In the atmospheric cycles, elements can move in the gaseous phase; examples include carbon and nitrogen.3. In sedimentary cycles, the element does not have a gaseous phase; an example is phosphorus.

7. Global Cycling of WaterA. Water is moved or stored by evaporation, precipitation, retention, and

transportation.1. A watershed funnels rain or snow into a single river.2. Nutrients are absorbed by plants to prevent their loss by leaching.

B. The Water Crisis1. Large-scale agriculture accounts for nearly two-thirds of the human population’s use of freshwater.

a. Salt buildup (salinization) of the soil and waterlogging can result.b. Withdrawal of underground water causes water tables to drop.

2. About one-third of the world’s population depends on groundwater for drinking water, but groundwater is being polluted by toxic chemicals leached from landfills and waste dumps.3. Human waste, insecticides, herbicides, chemicals, radioactive materials, and heat can pollute water.4. In the past decade, thirty-three nations have engaged in conflicts over reductions in water flow, pollution, and silt buildup.5. Most of the earth’s water is too salty for human consumption or for agriculture.

a. Desalinization processes are available and can be used when absolutely necessary.b. However, desalinization is not cost effective in most locales, and it uses valuable fuel reserves to provide the energy for the desalination equipment.

8. Carbon CycleA. Carbon enters the atmosphere (where it exists as carbon dioxide) by aerobic

respiration, fossil-fuel burning, and volcanic eruptions.1. Carbon is removed from the atmosphere (and bodies of water) by photosynthesizers and shelled organisms.2. Decomposition of buried carbon compounds millions of years ago caused the formation of fossil fuels.3. Burning of fossil fuels puts extra amounts of carbon dioxide into the atmosphere, an occurrence that may lead to global warming—the greenhouse effect.

B. Most researchers think the carbon buildup in the atmosphere is amplifying the greenhouse effect.

9. Greenhouse Gases, Global WarmingA. The greenhouse effect is the name for the warming action of the earth.

1. The greenhouse gases (carbon dioxide, water vapor, ozone, methane, nitrous oxide, and CFCs) trap heat as they escape from the earth back into space.2. Heat builds in the lower atmosphere—the greenhouse effect.

B. Evidence of Global Warming1. Temperatures have risen by one degree F since 1861.2. Nine of the ten hottest years have occurred since 1990.

10. Nitrogen CycleA. Nitrogen is a part of several steps in a cycling process.

1. In nitrogen fixation, bacteria convert N2 to NH3, which is then used in the synthesis of proteins and nucleic acids.

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2. By ammonification , bacteria and fungi breakdown nitrogenous compounds, forming ammonium.3. Nitrification is a type of chemosynthesis where NH3 or NH4

+ is converted to

NO2–; other nitrifying bacteria use the nitrite for energy and release NO3

–.4. Denitrification is the release of nitrogen gas to the atmosphere by the action

of bacteria (NO2– and NO3

– N2).B. Human Impact on the Nitrogen Cycle

1. Although the soil is enriched by nitrogen-fixing bacteria, soil nitrogen is still scarce due to leaching, denitrification, and farming methods that emphasize synthetic fertilizers.2. Air pollutants, including oxides of nitrogen, contribute to soil acidity.3. Heavy nitrogen applications not only are costly but also are lost in runoff and harvested crops.

11. Phosphorus CycleA. Phosphorus moves from land, to sediments in the seas, and back to the land in

its long-term geochemical phase of the cycle.1. In the ecosystem phase, plants take up the phosphorus from the soil; it is then transferred to herbivores and carnivores, which excrete it in wastes and their own decomposing bodies.2. Of all minerals, phosphorus is the most limiting factor in all natural ecosystems.

B. Runoff from agricultural applications of fertilizers adds large amounts of phosphorus to aquatic ecosystems; this is called eutrophication.

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