Nitrogen Cycle

url: http://www.teachersdomain.org/resource/lsps07.sci.life.eco.nitrogen/

Molecular Forms of Nitrogen

N2

NH4+

NO3-

NO2-

Nitrogen gas

Ammonium

NitrateNitrite

Nitrogen Changing Processes The process by which nitrogen-fixing bacteria

in the roots of legumes change atmospheric nitrogen to nitrates is called _______________________

The process by which N2 or organic nitrogen is changed to ammonium is called____________________

The two-step process of changing ammonium to nitrate is called _______________________

The process of changing nitrate into atmospheric nitrogen is called __________________

The process of changing nitrates into organic nitrogen is called ______________________

Nitrogen fixation

Ammonification

NitrificationDenitrificati

onAssimilati

on

Background Information

Nitrogen Fixation by nitrogen-fixing bacteria in the roots of

legumes

Ammonification by soil bacteria and fungi

Nitrification: Step 1

Nitrification: Step 2

Assimilation

Ammonification by Decomposers - decomposing

bacteria and fungi

Denitrification

The Whole Cycle

Nitrogen Cycle Summary

Process Bacteria N Changed from

N changed to

Nitrogen Fixation

Ammonification

Nitrification step 1

Nitrification step 2

Assimilation N/A

Denitrification

Nitrogen-fixing bacteria in

legume roots

Nitrogen in air Nitrate

Nitrogen-fixing bacteria in soil

Nitrogen in air AmmoniumDecay

bacteria and fungi

Organic nitrogen

Nitrifiying bacteria

Ammonium Nitrite

Nitrite

Nitrate

Nitrate

Organic nitrogen

Denitrifying bacteria Nitrate

Nitrogen in air

Discussion Questions

1. The atmosphere is 78% nitrogen: why do you think plants and animals can't use nitrogen as it is found in the atmosphere?

2. Explain what is meant by nitrogen fixation.

3. What is the role of bacteria in the nitrogen cycle?

4. Why don't legumes need nitrogen-containing fertilizers?

5. Why is nitrogen so important for living things?

1.Nitrogen fixation is the process that changes nitrogen from ______________

. The type of bacteria able to “fix” nitrogen are called

___________________________. Nitrogen fixing bacteria in legume roots allow

for nitrogen to be used by legume plants and become ____________________

nitrogen.

2. Nitrogen fixing bacteria in the soil change nitrogen from _________________

to ____________________ by a process called _________________________.

3. The nitrifying bacteria in the first white circle change nitrogen from

__________________________ to _____________________________ in a

process called ________________________________.

Nitrogen gas

nitrates organi

c

nitrogen gas

Ammomium

Ammonification

nitritenitrificati

on

Ammomium

4. This process is continued by a second group of nitrifying bacteria that change

nitrogen from _________________________ to _________________________.

5. Nitrates can follow one of two paths. If it is taken into a plant, it will be

_____________________________ into _____________________ nitrogen.

The chipmunk gets the nitrogen it needs by eating plants. Nitrogen containing

organic wastes from either plants or animals will be broken down by

___________________________ and ___________________________ into

__________________________________.

6. Denitrifying bacteria change nitrogen from ______________________________ to

_______________________________ returning it to the atmosphere.

nitrite

nitrates

assimilated organ

ic

decay bacteria

fungi

ammonium nitra

tenitrogen

gas