L13 - Nitrogen Cycle Flashcards
Why is nitrogen so important in life?
- a key constituent of cells
- exists in a number of oxidation states
- central element in proteins n DNA
What are the 4 major nitrogen transformations and describe them.
- Nitrification is the process by which ammonia (NH₃) is oxidized to nitrites (NO₂⁻) by Nitrosomonas and then to nitrates (NO₃⁻) by Nitrobacter bacteria.
- Denitrification is the reduction of nitrates (NO₃⁻) to nitrogen gas (N₂), typically carried out by Pseudomonas and other denitrifying bacteria under anaerobic conditions.
- Anammox is the anaerobic oxidation of ammonia (NH₃) to nitrogen gas (N₂) by Anammox bacteria in the presence of nitrites (NO₂⁻).
- Nitrogen fixation is the conversion of atmospheric nitrogen (N₂) into ammonia (NH₃) by nitrogen-fixing bacteria such as Rhizobium or through industrial processes like the Haber-Bosch method.
What is the most table form of nitrogen and is a in a major reservoir
N2
What is it called when prokaryotes use N2 as cellular nitrogen source?
nitrogen fixation
What is denitrification?
reduction of nitrate to gaseous nitrogen products and is teh primary mechanism by which N2 is produced biologically
Ammonia produced by nitrogen fixation or ammonification can be…
assimilated into organic matter or oxidized to nitrate
what is nitrogenase? what does it do?
enzyme that breaks triple bond to make nitrogen accessible. take nitrogen gas and uses a lot of energy to convert into 2 ammonia and releases energy from hydrolysis of ATP
What is Haber-Bosch process
an alternative to nitrogenase. nitrogen and hydrogen gases are passed over 4 beds of catalysts. uses industrial glass under extreme conditions to break triple bond (high pressure + temp + catalysts) to form ammonium
What is Anammox?
= anaerobic oxidation of ammonia to N2 gas. denitrification and anammox result in losses of nitrogen from biosphere
- anammox reaction (works under anaerobic conditions to oxidise ammonia)
- denitrification process (oxidised forms of nitrogen → nitrogenous gas)
Describe the oxidation states of nitrogen
reductive process from nitrate to nitrogen gas has to pass through intermediates which involves combinations of different organisms (reductive chain from +5 to 0)
In the process of nitrification, 2 groups of bacteria work in concert to oxidize ammonia fully to nitrate. what are the key enzymes, what are the diff reactions and what is the energy yield
- ammonia monooxygenase, hydroxylamine oxidoreductase, nitrite oxidoreductase
- organisms have low energy yield from these reactions so its very slow
- oxidation from ammonia (2 step)
- oxidation from nitrite to nitrate (single step)
Definition of anammox, anammoxosome
anammox = anoxic ammonia oxidation (performed by a ligature anaerobes = dont tolerate oxygen and only lives under anaerobic conditions)
anammoxosome = intracellular compartment where anammox reactions occur. protects cell. hydrazine is an intermediate of anammox which is toxic so it is in a compartment to protect cells)
Describe the assimilative metabolism and dissimilative metabolism (2 types of metabolism using same compounds)
- assimilative = cells gain compounds they can use in building their biological macromolecule. products are reduced to use in biosynthesis
- dissimilative = reduced products are not incorporated as cell but is excreted , used as acceptor for electrons
Is it true that in anaerobic respiration, electron acceptors other than O2 are used?
yes
Which yields more energy? aerobic or anaerobic?
aerobic
How does comparing the reduction potential inform us the reductive properties?
- positive = oxidative conditions
- compares how easy it is to reduce, the more negative the voltage the more reduced the state of nitrogen
- absense of oxygen → global conditions on early earth, these electron acceptors cant function
- most common electron acceptors bc they have the highest yields (nitrogen)
- products of nitrate reduction processes are gaseous (source of gaseous dinitrogen)
most organisms can carry out nitrate reduction to nitrite but can’t carry out full process to N2 gas. what is this problematic?
nitrous oxide is a potent greenhouse gas (more potent than methane). nitrogen rich fertilisers (partial denitrification of nitrate formed during fertilisation), NO2 released into soil into atmosphere which increases greenhouse gas
What is the difference between aerobic and anaerobic nitrate reduction?
Aerobic: Nitrate (NO₃⁻) is reduced to nitrite (NO₂⁻) in the presence of oxygen.
Anaerobic: Nitrate is reduced to nitrite or nitrogen gas (N₂) in the absence of oxygen.
What happens during an electron-accepting reaction when oxygen is the final electron acceptor?
In aerobic respiration, oxygen (O₂) is reduced to water (H₂O) by cytochrome complexes in the electron transport chain.
What is the function of nitrate reductase in the membrane?
Nitrate reductase reduces nitrate (NO₃⁻) to nitrite (NO₂⁻) using electrons from electron donors, typically under anaerobic conditions.
How does the reduction of NO₂⁻ lead to nitrogen gas in denitrification?
Nitrite (NO₂⁻) is sequentially reduced to nitric oxide (NO), nitrous oxide (N₂O), and eventually dinitrogen gas (N₂) by a series of enzymes and membrane proteins.
How have humans impacted the carbon and nitrogen cycles?
- increased CO2 = greenhouse gases
- air and ocean water temperature rising
- major impact on nitrogen cycle
- large amounts of nitrogenous fertilizers
- change in one will affect the other bc they are coupled
How does nitrogen enter and cycle through the environment?
Nitrogen enters the cycle through biological nitrogen fixation by bacteria, which convert atmospheric N₂ into usable forms like ammonia, contributing to soil and plant growth.
How does the nitrogen cycle function in the ocean and soil?
In the ocean, nitrogen is assimilated by phytoplankton, promoting algae growth. In soil, nitrifying bacteria convert ammonia to nitrates, some of which are released as N₂ into the atmosphere.
What is the impact of human activities on the nitrogen cycle?
Human activities, such as fertilizer use, add around 100 million tons of nitrogen annually, disrupting the natural nitrogen cycle and leading to environmental issues.
How is CO₂ converted to organic carbon, and what role does nitrogen fixation play in ecosystems?
CO₂ is converted to organic carbon mainly through photosynthesis, while nitrogen fixation is a biological process that embeds nitrogen into cellular material, supporting ecosystem growth.
How does nitrogen fixation affect primary production in ecosystems?
High nitrogen fixation boosts primary production by increasing available nitrogen, while low nitrogen fixation results in lower primary production due to nitrogen scarcity.
What are the effects of nitrification and denitrification on primary production?
Nitrification and denitrification both influence primary production; nitrification leads to nitrogen loss, reducing nitrogen availability and negatively affecting carbon fixation, creating a negative feedback loop.
