Abiotic Cycles 22.2

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Wnit" energ)/ flowsthroughon ecosystem, uater and minerals, such as carbon, nitrogen, calcium, and phosphorus. are recycled and reused. Each substance trauels through a

Definebiogeochemical cycle.

o Tracethestepsof thewatercycle.

biogeochemical ( wt-oh-ctt-oh-KEM-i_kuhl) cycle, mou ing from the abiotic portion of the enuironment, suchas the atmosphere,into liuing things,and back again.

I Summarize themajorsteps inthenitrogen cycle.

a Describe thesteps of thecarbon cycle.

THE \ruATER CYCLE water is crucial to life. cells contain 70 percent to 90 percent water, and water provides the aqueous environment in which most of liteu chemical reactions occur. The availability of water is one of the kep factors that regulate the productivity of terrestrial ecosystem , However, very little of the available water on Earth is trapped withi@ living things at any given time. Bodies of water such as lakes, river6. streams, and the oceans contain a substantial percentage of ttp Earth's water. The atmosphere also contains water-in the form d water vapor. In addition, some water is found below ground. wats in the soil or in underground.folmations of porous rock is known an :,

FIGURE 22-5 In the water cycle, waterfallsto Earth's I surface precipitation. as Some water I reenters the atmosphere by evaporation I Some waterrunsinto I andtranspiration. lakes, rivers, andoceans.0ther I streams, through thesoilandinto I waterseeps ground the water. Follow thepathways I I of thewatercyclein thefigure.

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ground water. The movement of water between these various reser'.oirs, known as the water cycle, is illustrated in Figure 22-5. Three important processes in the water cycle are evaporation, :ranspiration, and precipitation. Evaporation adds water as vapor :o the atmosphere. Heat causes water to evaporate from the ,:(eans and other bodies of water, from the soil, and from the bod_ resof living things. At least 90 percent of the water that evaporates :rom terrestrial ecosystems passes through plants in a process called transpiration. In transpiration, plants take in water through ireir roots, and they release water and take in carbon dioxide irrough the stomata in their leaves. Animals also participate in the 'h,-atercycle, but their impact is less significant than that of plants. Animals drink water or obtain it from their food. They release this b-aterwhen they breathe, sweat, or excrete. water leaves the atmosphere through precipitation. The amount n[ rrater the atmosphere can hold depends on abiotic factors, such ds temperature and air pressure. once the atmosphere becomes sarurated with water vapor, precipitation occurs in the form of raia. snow, sleet, hail, or fog.

TFIE CARBON

CYCLE

liliiryether,photosynthesis and cellular respiration form the basis of ' '- carbon cycle, which is illustrated in Figure 22-6.During photos5m_ tfdi'tpsis. plants and other autbtrophs use carbon dioxide (COr), along mfi water and solar energy,to make carbohydrates. Both autotrophs ;snr heterotrophs use oxygen to break down carbohydrates during Carbon dioxide

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Death and decomposition

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:==.:: Modeling Ground Water Materialsdisposable gloves, lab apron, 3 L plastic bottle(cutin half), (250mL),dry smallstones sodwithgrass, watet,graduated cylinder, 500mLbeaker Procedure

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1. P uton yourl abapronand disposable gloves. 2. Invertthetop halfof the plastic bottleandplaceit insidethe bottomhalfof the bottleto forma column. 3. Place the stonesin the bottom of the inverted top halfof the bottle.Placea chunkof drysod with grasson top of thesrones. 4. Pour250mL.ofwateroverthe sod,andobservehow the water penetrates thesoilandmoves throughthecolumn. 5. Whenthewateris no longer draining, remove thetop half of thecolumnandpourthe waterfromthe bottomof the columnintoa beaker. Measure thevolumeof liquidin the beaker. Analysis Whatis thevolumeof thewaterthatdrained through thesod?Howmuchof thewater remained in thesoil?Whereooes thewatergo whenapplied to a reallawnor crop?Whatmightthe fateof fertilizeror pesticides be thatareappliedto a lawnor crop?

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Carbon existsin theatmosphere in the formof carbondioxide. Cellular resoiration,combustion, anddecomposition of organicmatterarethe threemajor sources of carbondioxide. Byburning largeamounts of fossilfuels,humans areincreasing the amountof carbon dioxidein theatmosphere.

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cellular respiration. The byproducts of cellular respiration are carb dioxide and water. Decomposers release carbon dioxide into :' atmospherewhen they break down organic compounds.

Er:€?aaeraee*xr €EeeCarb*ea Cy*E* F{urc"ae.E't In the last 150 years, the concentration of carbon dioxide in t:, atmosphere has risen nearly 30 percent. Almost half of this increa.. has occurred in the last 40 years. Human activities are responsi: for the increase. Our industrial society depends on the ener.released by the burning of fossil fuels-coal, oil, and natural ga'. Fossil fuels are the remains of organismsthat have been transforrni: by decay, heat, and pressure into energy-rich organic molecule'. Burning releasesthe energy in these molecules, but it also releas=": carbon dioxide. Carbon dioxide is also added to the atmosphere : the burning of vegetation.Today large areasof tropical rain forest ar. being burned to create farmland and pasture for cattle. The burnirof vegetation adds carbon dioxide to the atmosphere, and tf-. destruction of vegetation removes plants that could have absorb':: carbon dioxide from the atmosphere through photosynthesis.

FIGURE22-7

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Thisfigureshowsthe cyclingof nitroare Bacteria genwithinan ecosystem. for manyof the stepsin the responsible theconversion including cycle, nitrogen intoammonia. nitrogen of atmospheric livein thesoil bacteria Nitrogen{ixing or in the rootsof plants.Plantstakeup produced by thebacteria. theammonia getnitrogen by eatingplants Animals or otheranimals.

AII organisms need nitrogen to make proteins and nucleic acic. The complex pathway that nitrogen follows within an ecosystem'. called the nitrogen cycle. Consider how nitrogen cycles within ti-. terrestrial ecosystemshown in Figure 22-7.Nitrogen gas,Nr, mak:. up about 78 percent of the atmosphere,so it might seem that njtr-gen would be readily availablefor living things. However,shortag=.

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Denitrifying \ bacteria

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Waste Death Death i (urine and feces)

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Nitrates S-

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l{itrogen-fixing ba;teria in soil

of nitrogen often limit the productivity of plants-and therefore the productivity of ecosystems.Most plants can use nitrogen only in ihe form of nitrate. The process of converting nitrogen gas to :ritrate is called nitrogen fixation. organisms rely on the actions of lacteria that are able to transform nitrogen gas into a usable form. separate groups of nitrogen-fixing bacteria convert nitrogen gas urto ammonia, then nitrite, and then nitrate, which plants can use. Nitrogen-fixing bacteria live in the soil and in the roots of some hinds of plants, such as beans, peas, clover, and alfalfa.These plants inve evolved a complex mutualistic relationship with nitrogen-fixing aacteria. The plant provides the bacteria with a home-airtight su'ellings on its roots-and supplies them with carbohydrates. In atchange,the bacteria produce usable nitrogen for the plant. Excess itrogen produced by the bacteria is released into the soil.

Recycling Nitrogen The bodies of dead organisms contain nitrogen, mainly in proteins and nucleic acids. Urine and dung also contain nitrogen. Decomfosers break down the corpses and wastes of organisms and rclease the nitrogen they contain as ammonia. This process is ffiiown as ammonification (ah-vntru-i-fi-KAy-shuhn). Through ammon_ Ldcation,nitrogen that would otherwise be lost is reintroduced into :he'ecosystem. Bacteria in the soil take up ammonia and oxidize it into nitrites, IO, , and nitrates, NOr-. This process, called nitrification m:-tri-fi-KAY-shuhn), is carried out by bacteria. The erosion of nitratench rocks also releases nitrates into an ecosystem. plants use a.itrates to form amino acids. Nitrogen is returned to the atmosF,irerethrough denitrification. Denitrification occurs when anaeron,icbacteria break down nitrates and release nitrogen gas back into rne atmosphere. Plants can absorb nitrates from the soil, but animals cannot. Animals obtain nitrogen in the same way they obtain energy_by eating plants and other organisms and then digesting the proteins ;andnucleic acids.

1. Descibethe biogeochemical cycle. 2. Wheredo nitrogen-fixing bacterialive?What crucialfunctiondo they perform? 3. Describe the roleof decomposers in the nitrogen cycle. 4. Howhasthe burningof fossilfuelsaffectedthe carboncycle?

5. Throughwhat process doesmostwatervapor enterthe atmosphere? Explainthe process. 6. CRITICAL THINKING Exptain two waysthat the burningof vegetationaffectscarbondioxidelevels in the atmosphere. Howdo you think the removalof vegetationaffectsoxygenlevelsin the atmosphere?

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