The Nitrogen Cycle - CAMBRIDGE-SOUTH DORCHESTER HIGH...

ECOLOGY•Activity8•LivingonEarth

©2011TheRegentsoftheUniversityofCalifornia

SGI Ecology: Activity 8 • Living on Earth

The Nitrogen Cycle

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Why is nitrogen important?

• Nitrogenisessentialtolivingorganisms

• Itisfoundinallaminoacids,whichmakeupproteins

• ItispartofDNAandRNA



Where does nitrogen come from?

• Nitrogenisfoundinmanychemicalforms(ammonia,nitrates,etc),onlysomeofwhichcanbeusedbyorganisms

• Nitrogenmakesup78%oftheair,butmostorganismscannotusenitrogendirectlyfromtheair

• Nitrogeniscycledbetweentheatmosphere,organisms,anddifferentreservoirsinaprocesscalledthenitrogencycle

• Duringthiscyclenitrogenistransformedintoseveralchemicalforms



The Nitrogen Cycle



Nitrogen-fixing Bacteria• Nitrogen‐fixingbacteriatransformatmosphericnitrogen(N2)intoammoniumcompounds(NH4

+)

• Symbioticnitrogen‐fixingbacterialiveinrootsoflegumefamilyplant(soy‐beans,peanuts,etc)

• Othertypesofnitrogen‐fixingbacteriaarefoundinthesoil



Organisms and Nitrogen• Plantsandotherproducersassimilatenitrogen,transformingitfromnitrate(NO3

–)orammonium(NH4

+)ionstoformbiomass.

• Consumersobtainnitrogenfromeatingproducers,orfromeatingotherorganismsthathaveeatenproducers.



Decomposers and Nitrogen

• Decomposers,primarilybacteriaandfungi,breakdowndeadorganisms.

• Decomposerstransformnitrogenfromorganismsintoammonium(NH4

+)whichgoesintothesoil.



Nitrifying Bacteria

• Nitrifyingbacteriabreakdownammonium(NH4

+)intonitrite(NO2–)

andthenintonitrate(NO3

–)

• Nitrate(NO3–)

isassimilatedbyorganismsortransformedbydenitrifyingbacteria



Denitrifying Bacteria

• Nitrate(NO3–)inthesoil

istransformedbydenitrifyingbacteriaintoatmosphericnitrogen(N2).

• DenitrifyingbacteriaalsoproduceN2O,whichcontributestothegreenhouseeffect.



Atmospheric Nitrogen

• Atmosphericnitrogen(N2)cannotbeuseddirectlybymostproducersorconsumersandmustbetransformedbybacteria.



Leaching• Nitrateionsarelostfromthesoilthroughleaching.

• Water‐solublenitrateionsmovewithwaterthroughthesoilandcancontaminatenearbygroundwaterorbodiesofwater.

• Leachingcanleadtopoorsoilconditionsandeutrophicationofcontaminatedwaterbodies.



The Nitrogen Cycle

The Nitrogen Cycle - CAMBRIDGE-SOUTH DORCHESTER HIGH...

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