Nitrogen Cycle Flashcards
What can you tell me about nitrogen?
N2 gas = ~78% of Earth’s atmosphere by volume
N = proteins + nucleic acids
therefore, essential for life
N2 = unusable for plants & animals
therefore, do not have enzymes to ‘fix’ atmospheric N
What are the steps involved in the nitrogen cycle?
nitrogen fixation
nitrogen assimilation
ammonification
nitrification
denitrification
What are the bacteria involved in the nitrogen cycle, where are they found, what are their purpose?
rhizobium - nitrogen fixation
found in roots of legume plants
azotobacter - nitrogen fixation
free-living in soil
photosynthetic cyanobacteria - nitrogen fixation
found in aquatic ecosystems that get sunlight
nitrosomonas - nitrification (NH3 to NO2)
nitrobacter - nitrification (NO2 to NO3)
pseudomonas - denitrification
Explain the process of nitrogen fixation to me
nitrogen gas undergoes the process of nitrogen fixation by specialised bacteria, rhizobium and azotobacter. Once the nitrogen gas has been converted into ammonia, the bacteria nitrosomonas transforms it into NO2 and then nitrobacter transforms that into NO3. Plants can then absorb the nitrogen.
PURPOSE: CONVERT N2 INTO USABLE FORM (NO3)
What can these bacterias be classified as?
chemoautotrophs as they derive energy for nitrogen fixation from the bonds in the compounds they convert
What is nitrogen fixation?
any natural or industrial process that causes free nitrogen (N2), which is a relatively inert gas, to combine chemically wt other elements to form more-reactive, inorganic nitrogen compounds such as ammonia, nitrates or nitrites
How does nitrogen enter the living world?
bacteria & other single-celled prokaryotes & blue-green algae (90%)
(makes organic molecules later incorporated in organisms’ bodies, broken down, excreted (e.g. urea in urine))
abiotic means - lightning, ultraviolet radiation & Haber-Bosch process (10%)
(turn N2 into usable form (NH4) AKA nitrogen fixation)
Describe the relationship btw plants and nitrogen fixing bacteria
mutualism - both organisms benefit
rhizobium - grow to form nodules on roots of legume plants
plant supplies carbohydrates to bacteria to use for respiration
bacteria fixes ammonia to legume
legume requires ammonia for synthesis of amino acids
What can you tell me about nitrogen fixation in the industry?
Haber-Bosch process - directly synthesises ammonia from nitrogen and hydrogen in most economial nitrogen-fixation process known
N2 + H2 + EXTREME PRESSURE + MODERATELY HIGH TEMPS + active catalyst ——–> yield extremely high proportion of ammonia
starting point of wide range of nitrogen compounds (e.g. FERTILISER)
made feasible by Carl Bosch
What is involved in the process of nitrification?
a process carried out by nitrifying bacteria, transforms soil ammonia into nitrates (NO3) thich plants can use in their tissue
nitrosomonas - NH4 –> NO2
nitrobacter - NO2 —> NO3
Why can plants absorb nitrates but not ammonia?
nitrates are surrounded by oxygen atoms, enabling it to be brought into plants through their roots to be used
What is nitrogen assimilation?
is the formation of organic nitrogen compounds like amino acids from inorganic nitrogen compounds present in environment
Why is nitrogen assimilation important?
bc organisms such as plants, fungi & certain bacteria cannot fix nitrogen gas
therefore, depend on ability to assimilate nitrate or ammonia for their needs
other organisms, like animals, depend entirely on organic nitrogen
What can you tell me about ammonification?
takes place due to decomposers (which break down animal & plant cells into simpler substances) making nutrients available in the ecosystem
process of ammonification converts organic nitrogen (the way nitrogen contained is in contained in lining organisms) into inorganic ammonia (NH3) or ammonium ions (NH4)
dead animal/plant body & their wastes include organic nitrogen
therefore, MUST RETURN TO ECOSYSTEM IN FORMS THAT ARE USABLE
therefore, ammonification returns nitrogen to soil/water so plants can pass it along food chain
What is denitrification?
nitrogenous compounds from dead organisms / wastes are converted into nitrites & nitrates which are then turned into nitrogen gas by denitrifying bacteria
SHORT: reduces the availability of nitrogen compounds to plants
What are denitrifying bacteria?
PSEUDOMONAS
microorganisms whose actions result in the conversion of nitrates in soil to free atmospheric nitrogen
THUS deleting soil fertility & reducing agricultural productivity
Why is denitrification important?
without denitrification Earth’s supply of nitrogen would accumulate in oceans
moreover, since nitrates are highly soluble, they are continuously leached from soil into nearby bodies of water
What is essential for cellular respiration (in regards to denitrification)?
electron transport!
O / nitrate can be used as an electron acceptor in electron transport
thought O is preferred in O poor conditions nitrate is used & the process releases nitrogen gas as a product
PSEUDOMONAS!!!
What encourages denitrification?
waterlogged conditions - due poor drainage & irrigation / flooding
= reduces O in soil
= encourage denitrification as less O is available so nitrates have to be used for respiration of denitrifying bacteria - PSEUDOMONAS!
Draw the nitrogen cycle
YEESESESE BBABBBAABBEE!!
Is nitrogen a limited nutrient?
Yes
nitrogen = primary production + decomposition + etc
therefore, if nitrogen was unlimited organisms would be larger
HOWEVER it is often a lilting nutrient = limits growth of pops and organisms
How do you tell if a nutrient is limited?
- adding more of that nutrient = increase growth
2. IF NON-LIMITING nutrient added = no effect
How is human activity affecting the nitrogen cycle?
~450 million metric tons of nitrogen is fixed using Haber-Bosch process = used for fertilisers
human activity = release of nitrogen into environment
2 main means:
- combustion of fossil fuels
- use of nitrogen-containing fertilisers
= increase atmospheric nitrogen
atmospheric nitrogen is harmful if not in N2 form (e.g. acid rain & greenhouse effect)
What is eutrophication due to excess fertiliser runoff?
nutrient runoff = overgrowth / bloom of algae & other microorganisms (due to nitrogen abundance)
eutrophication = reduction of O in water bc algae & co feed on them = large amounts used for respiration = death of other organisms + low-O, species-depleted areas (dead zones)
What is eutrophication?
is characterised by excessive plant & algal growth due to the increased availability of 1 or more limiting growth factors needed for photosynthesis (e.g. sunlight, CO2 & nutrient fertilisers)
Is eutrophication natural or man-made?
occurs naturally over centuries as lakes age & fill wt sediments
HOWEVER, human activity = accelerated rate & extent of eutrophication through point-source discharge & non-point loadings of limiting nutrients (of N & P) into aquatic environments
= DRAMATIC CONSEQUENCES for drinking water sources, fisheries & recreation
What causes eutrophication?
scientists linked algal blooms to nutrient enrichment resulting from anthropogenic activities
e.g. agriculture, industry & sewage disposal
What are the consequences of eutrophication?
- Creation of dense blooms of phytoplankton (noxious) = reduce water clarity & quality
- Blooms of blue-green algae (cyanobacteria)
=limit light penetration = reduce growth = die-offs of plants = lowering success of predators
=nigh rates of photosynthesis = depletion of dissolved inorganic carbon = increase pH = impairing organisms which rely on perception of dissolved chemical cues
= tainted drinking water & recreational opportunities & hypoxia
What are dead zones?
when dense algal blooms die = microbial decomposition = depletion of dissolved O = hypoxic / anoxic ‘dead zone’
dead zone = lack of sufficient oxygen to support most organisms
often found in freshwater during summer
hypoxia & anoxia = threat to lucrative commercial & recreational fisheries
What are the threats of toxins due to eutrophication?
algal blooms = potential noxious toxins
harmful algal blooms (HABs) = degradation of water quality + destruction of economically important fisheries + public health risks
toxigenic cyanobacteria (phytoplankton) dominate nutrient-ruich freshwater ecosystems due to superior competitive abilities under high nutrient concentrations, low nitrogen-to-phosphorous ratios, low light levels, reducing mixing & high temps
poisoning of domestic animals, wildlife & humans has been documented
