NITROGEN CYCLE

PREPARED BY: JEANELLE A.

NEVARES BSEd 2C Biosci

Major

What is Nitrogen?Nitrogen (N) is an essential

component of DNA, RNA, and proteins, the building blocks of life.

All organisms require nitrogen to live and grow.

The majority (78%) of the Earth’s atmosphere is N2.

Nitrogen’s triple bond• Although the majority of the

air we breathe is N2, most of the nitrogen in the atmosphere is unavailable for use by organisms.

• This is because the strong triple bond between the N atoms in N2 molecules makes it relatively inert (like a noble gas).

How Can We Use N2?• In order for plants

and animals to be able to use nitrogen, N2 gas must first be converted to more a chemically available form such as ammonia (NH3) or nitrate (NO3

-).

WE CAN’T!

But it IS POSSIBLE THROUGH NITROGEN CYCLE!

THE NITROGEN CYCLE

THE NITROGEN CYCLENitrogen in

the airanimal protein

dead plants & animalsurine & feces

ammonia

nitritesnitrates

plant madeprotein

decomposition by bacteria & fungi

bacteria

nitrates absorbed(nitrifying bacteria)

denitrifyingbacteriaroot nodules

(containing nitrogen fixing bacteria)

nitrogen fixing planteg pea, clover

bacteria

THE FIVE PROCESSES IN THE NITROGEN CYCLE Nitroge

n Fixatio

n Nitrogen Assimilati

on

AmmonificationNitrificati

on

Denitrification

1. Nitrogen Fixationis the process in which the N2

compound in the atmosphere breaks and combines with other compounds. The nitrogen is FIXED when it combines with HYDROGEN or OXYGEN. NN

HN HH

N2

Ammonia (NH3)

Nitrous Oxide (N2O)

Three ways to “fix” NitrogenMain process: Special bacteria

convert the nitrogen gas (N2) to ammonia (NH3), which only some plants can use (peas, beans).

Lightning strikes convert N2 to N2O or NO3.

Industrial production. Chemical manipulation turns N2 into NH3 (Fertilizer)

2. Nitrogen AssimilationThe process of absorbing Nitrates

and Ammonia into Organic Nitrogen.

this organic nitrogen is transferred to animal’s body when plants are eaten by the animals.

3. AmmonificationOrganic N --> NH4

+

Also called Nitrogen Mineralization.Decay of dead things, manure, etc. Done by decomposers (bacteria,

fungi, etc.) During this process, a significant

amount of the nitrogen contained within the dead organism is converted to ammonium (NH4

+).

4. Nitrification NH3 or NH4

+ --> NO2- --> NO3

-

(Nitrifying) Bacteria add oxygen to nitrogen in two steps:

STEP 1: Bacteria take in NH3 or NH4

+ & make NO2

- = nitriteStep 2:

Bacteria take in NO2- & make NO3

- = nitrate

5. Denitrification NO3

- --> N2

(Denitrifying) Bacteria do it.

removes a limiting nutrient from the environment and converts it back to atmospheric N2.

Human Impact• FERTILIZERS!

• Extra nitrogen fertilizer can runoff, where it contaminates surface water or infiltrates into ground water.

• In drinking water, excess nitrogen can lead to cancer in humans and respiratory distress in infants.

Human Impact• In surface waters, extra nitrogen can

lead to nutrient over-enrichment.

• This leads to –fish-kills, –harmful algal blooms, –and species shifts in

aquatic and land ecosystems.