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Flashcards in Nitrogen Cycle Deck (32)

what is the process of mineralization?

When plants and animals die, microorganisms degrade their tissues. These microorganisms convert the complex organic material first into inorganic forms and then into forms that can be then taken up by organisms and converted into living tissue again


what is the significance of plants and what critical role do they play in?

they play a critical role in energy cycling as primary producers


what is a primary producer?

life forms that are able to capture energy from the sun and utilize it to fix atmospheric CO2 into organic carbon.


What are the limiting organic materials in plants?

1. Nitrogen
2. phosphorus


Inorganic forms of nitrogen?

1. N2 gas
2. Ammonia
3. Nitrate
4. nitrite


Organic forms of nitrogen?

1. amino caids
2. nucleic acids
3. urea


Problem with dinitrogen?

organisms cannot use N2 unless it has been reduced to ammonia (NH3) through nitrogen fixation (reduction)


Examples of natural processes in nitrogen fixation?

Lightning, volcanic eruptions, uv light


2 best way to do nitrogen fixation?

1. Soil microbes such as Rhizobium
2. Aquatic forms such as the cyanobacterium Anabaena


Significance of ammonia formed by nitrogen fixation(reduction of nitrogen)?

It serves as a direct/indirect nitrogen source for plants and animals and once absorbed, it can be converted to cellular components such as amino acids, purines, and pyrimidines


2 pathways for the use of ammonia by plants?

1. Assimilation of ammonia
2. oxidation of ammonia to nitrate (nitrification) and its subsequent use


What are the two main sources of ammonia in the environment?

1. nitrogen fixation
2. ammonification


Explain process of ammonification?

this process is the result of decomposition of dead animals and plants


explain the process of microbial action and their contribution to the release of ammonia?

1. microbial action causes the hydrolysis of proteins and nucleic acids, releasing the amino acids and nucleotides
2. the nucleotides and amino acids are then further metabolized by microorganisms and the nitrogen released as ammonia


what happens to ammonia produced by microbial action in the soil?

it is mostly absorbed by other microorganisms (very little by plant roots), and then taken into cell material. this is known as ammonia assimilation.


what happens to the assimilated(taken up) nitrogen ?

it gets incorporated into cellular proteins and nucleic acid and travels through the food chain with little loss.


What happens to the nitrogen that is uptaked into an organism?

1. it can either be lost through extretion as urea or ammonia
2. or it simply reincorporates itself into other nitrogenous compounds in the cell for as long as an organism is alive or when another organism eats it.


When can the nitrogen content of plants or animals can be released as N2?

upon natural death and decomposition


Explain the oxidation of ammonia to nitrate (nitrification)

in well aerated soils, two groups of strictly aerobic bacteria have the capacity to oxidize ammonia to nitrite and then further to nitrate. The two processes involve different bacteria and this entire oxidative process (nitrification) allows the bacteria to use the high-energy electrons thus released in the production of energy.


What is the source of the high-energy electrons that the bacteria uses to reduce ammonia to nitrite and nitrate

. it comes from an inorganic compound.


What is chemolithotrophic?

bacteria that uses high-energy electrons from an inorganic compound as a source


What is nitrate assimilation ?

the process of nitrate uptake and utilization


Conditions for the microbes involved in nitrification. (where does it work well?)

1. well aerated, warm, most soils


Significance of Nitrate?

its the most useful form of nitrogen for plants


Pros about nitrate assimilation by plants?

its the most profitable use of nitrates in soil or water.


Two ways a plant can uptake nitrogen?
which is more efficient?

1. absorbs ammonia through its roots
2. absorbs nitrogen in form of nitrate


Two possible pathways for nitrate use by microbes?

1. assimilatory nitrate reduction
2. Dissimilatory nitrate reduction or denitrification:


Explain assimilatory nitrate reduction

there are microorganisms that can convert nitrate to nitrite and then ammonia (reverse reaction). The ammonia may not be very useful to plants but it can be absorbed by microbes and be taken up into cell material.


Goal of assimilatory nitrate reduction?

it has the virtue of keeping the nitrogen in a state in which it can still be absorbed and used by living organisms


Explain dissimilatory nitrate reduction or denitrification:

Organisms can use any existing nitrate or nitrite as terminal electron acceptors in order to continue to produce energy if soils are so poorly aerated. this form of anaerobic respiration (oxygen not being a terminal electron acceptor) results in nitrate being reduced to nitrite and further reduced to nitrogen gas. this form of nitrate reduction DOES NOT RESULT IN the incorporation of nitrogen into the cells.


what is nitrate reduction?

reduction of nitrate to nitrite


what is denitrification?

reducing nitrite to nitrogen gas