TheNitrogen Cycle

1. What is nitrogen?

1. Nitrogen is a non-metal, gaseous element.

2. Where is nitrogen found in the environment?

2. The largest single source of nitrogen is in the atmosphere.

Nitrogen makes up 78% of our air!

3. What happens to atmospheric nitrogen(N2) in the nitrogen

cycle?N

N

N N

N

N

3. Atmospheric nitrogen is converted to ammonia or nitrates.

Ammonia (NH3) Nitrates (NO3)

Atmospheric Nitrogen (N2)

N

N

N

N

4. Why does atmospheric nitrogen

need to be converted?

N

N

N

N

N

N

5. Nitrogen is an essential component of DNA, RNA, and proteins—the building

blocks of life. Although the majority of the air we breathe is nitrogen, most living organisms are

unable to use nitrogen as it exists in the atmosphere!

6. How does atmospheric nitrogen get

changed into a form that can be

used by most living organisms?

N

N

6. By traveling through one of the four processes in the Nitrogen Cycle!

(A) Nitrogen Fixation

(C) Nitrification (B) Ammonification

(D) Denitrification

Nitrogen Cycle

The first process in the nitrogen cycle is…Nitrogen Fixation!

(1) Nitrogen Fixation

Nitrogen Cycle

7. What is “nitrogen fixation”

and what does it mean

to say nitrogen gets

“fixed”?

N

N

7. “Nitrogen Fixation” is when the nitrogen gets “fixed” and combines with oxygen or hydrogen.

N

N

N

N

NOxygen

Hydrogen

Oxygen

Hydrogen

N

There are three ways that nitrogen gets “fixed”!

(a) Atmospheric Fixation

(b) Industrial Fixation

(c) Biological Fixation

Bacteria

(A)Atmospheric Fixation(Only 5 to 8% of the Fixation

Process)Lightning breaks nitrogen

molecules apart and combines with oxygen forming nitrogen oxides (N2O). Nitrogen oxides

dissolve in rain, forming nitrates. Nitrates (NO3) are

carried to the ground with the rain.

Lightning “fixes” Nitrogen!

Nitrogen combines with Oxygen

Nitrogen oxides forms

Nitrogen oxides dissolve in rain and change to nitrates

Plants use nitrates to grow!

(NO3)

NN O

(N2O)

(B) Industrial FixationUnder great pressure, at

a temperature of 600 degrees Celcius, and

with the use of a catalyst, atmospheric

nitrogen (N2) and hydrogen are combined to form ammonia (NH3). Ammonia can be used as

a fertilizer.

Industrial Plant combines nitrogen and hydrogen

Ammonia is formed

Ammonia is used a fertilizer in soil

(NH3)

NNH

N H3

( C) Biological Fixation(where MOST nitrogen fixing is completed)

There are two types of “Nitrogen Fixing Bacteria”

Free Living Bacteria(“fixes” 30% of N2) Symbiotic Relationship

Bacteria(“fixes” 70% of N2)

Most atmospheric nitrogen (N2) is “fixed” and changed to ammonia (NH3). Ammonia is highly toxic to many organisms. Can plants use ammonia?

Very few plants can use ammonia (NH3)…

…but, fortunately the second process

Ammonification can help!

(1) Nitrogen Fixation

(2) Ammonification

8. What is ammonification?

8. Ammonification: Bacteria decomposers break down amino acids from dead animals and wastes into nitrogen

ammonium.

Bacteria decomposers break down amino acids into ammonium

9. Why is ammonification

necessary?

9. Because plants cannot use the organic forms of nitrogen that are in the soil as a result of:(1) wastes (manure and sewage)(2) compost and decomposing roots and leaves

10. How does ammonification

occur?

10. Microorganisms convert the organic nitrogen to ammonium. The ammonium is either taken up by the

plants (only in a few types of plants) or is absorbed into the soil particles. Ammonium (NH4) in the soil is stored up to later be changed into inorganic nitrogen, the kind

of nitrogen that most plants can use.

Ammonium (NH4) is stored in soil.

Bacteria converts organic nitrogen to ammonium (NH4)

Ammonium (NH4) is used by some plants

Bacteria

What happens to ammonium (NH4) stored

in the soil?

11. It travels through thethird process

of the nitrogen cycle called Nitrification!

(1) Nitrogen Fixation

(2) Ammonification(3) Nitrification

11. Nitrifying bacteria in the ground first combine ammonia with oxygen to form nitrites. Then another group of nitrifying bacteria convert nitrites to nitrates

which green plants can absorb and use!

Nitrifying bacteria in soil combine ammonia with oxygen

Ammonia changes to nitrites

Nitrifying bacteria in soil convert nitrites to nitrates

Plants absorb nitrates and grow!

Ammonia Nitrites Nitrates

(NH3) (NO3)(NO2)

12. How does nitrogen reenter the atmosphere

in the nitrogen

cycle?

12. Through the fourth process called denitrification!

(1) Nitrogen Fixation

(2) Nitrification(3) Ammonification

(4) Denitrification

13. What does denitrification

do?

13. Denitrification converts nitrates (NO3) in the soil to atmospheric nitrogen (N2) replenishing the

atmosphere.

Nitrates (NO3) in Soil

Nitrogen in atmosphere (N2)

Other ways that nitrogen returns to the atmosphere…

Emissions from industrial combustion and gasoline engines create nitrous oxides gas (N2O).

Volcano eruptions emit nitrous oxides gas (N2O).

Can you fill in the following diagram with the parts of the nitrogen cycle?

Word bank:denitrification,nitrification,

nitrogen fixation,ammonification

(1) _____________

(3) ____________ (2) _____________

(4) _____________

Nitrogen Cycle

Nitrates in SoilAmmonia is converted to nitrites and nitrates.

Organic nitrogen is converted to ammonium.

(a)

(b)

(c)

N2

NH3

NO3

N2O

(1) Nitrogen Fixation

(3) Nitrification

(2) Ammonification

(4) Denitrification

Nitrogen Cycle

Nitrates in SoilAmmonia is converted to nitrites and nitrates.

Organic nitrogen is converted to ammonium.

(a)

(b)

(c)

N2

NH3

NO3

N2O