Nitrogen cycleThe nitrogen cycle is the biogeochemical cycle by which nitrogen is converted into multiple chemical forms as it circulates among atmospheric, terrestrial, and marine ecosystems. The conversion of nitrogen can be carried out through both biological and physical processes. Important processes in the nitrogen cycle include fixation, ammonification, nitrification, and denitrification. The majority of Earth's atmosphere (78%) is atmospheric nitrogen, making it the largest source of nitrogen.
Nitrogen fixationNitrogen fixation is a chemical process by which molecular nitrogen (N2), which has a strong triple covalent bond, is converted into ammonia (NH3) or related nitrogenous compounds, typically in soil or aquatic systems but also in industry. The nitrogen in air is molecular dinitrogen, a relatively nonreactive molecule that is metabolically useless to all but a few microorganisms. Biological nitrogen fixation or diazotrophy is an important microbe-mediated process that converts dinitrogen (N2) gas to ammonia (NH3) using the nitrogenase protein complex (Nif).
NitrogenNitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at seventh in total abundance in the Milky Way and the Solar System. At standard temperature and pressure, two atoms of the element bond to form N2, a colorless and odorless diatomic gas. N2 forms about 78% of Earth's atmosphere, making it the most abundant uncombined element in air.
DenitrificationDenitrification is a microbially facilitated process where nitrate (NO3−) is reduced and ultimately produces molecular nitrogen (N2) through a series of intermediate gaseous nitrogen oxide products. Facultative anaerobic bacteria perform denitrification as a type of respiration that reduces oxidized forms of nitrogen in response to the oxidation of an electron donor such as organic matter.
Biogeochemical cycleA biogeochemical cycle, or more generally a cycle of matter, is the movement and transformation of chemical elements and compounds between living organisms, the atmosphere, and the Earth's crust. Major biogeochemical cycles include the carbon cycle, the nitrogen cycle and the water cycle. In each cycle, the chemical element or molecule is transformed and cycled by living organisms and through various geological forms and reservoirs, including the atmosphere, the soil and the oceans.
Human impact on the environmentHuman impact on the environment (or anthropogenic environmental impact) refers to changes to biophysical environments and to ecosystems, biodiversity, and natural resources caused directly or indirectly by humans. Modifying the environment to fit the needs of society (as in the built environment) is causing severe effects including global warming, environmental degradation (such as ocean acidification), mass extinction and biodiversity loss, ecological crisis, and ecological collapse.
EnzymeEnzymes (ˈɛnzaɪmz) are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. Almost all metabolic processes in the cell need enzyme catalysis in order to occur at rates fast enough to sustain life. Metabolic pathways depend upon enzymes to catalyze individual steps.
Oxidation stateIn chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to other atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. Conceptually, the oxidation state may be positive, negative or zero. While fully ionic bonds are not found in nature, many bonds exhibit strong ionicity, making oxidation state a useful predictor of charge. The oxidation state of an atom does not represent the "real" charge on that atom, or any other actual atomic property.
Actinorhizal plantActinorhizal plants are a group of angiosperms characterized by their ability to form a symbiosis with the nitrogen fixing actinomycetota Frankia. This association leads to the formation of nitrogen-fixing root nodules. Actinorhizal plants are dicotyledons distributed among three angiosperm orders, 8 families and 25 genera: These three orders form a single clade within the Rosids, which is a sister taxon to the other major nitrogen-fixing order, the Fabales. All actinorhizal species are trees or shrubs, except for the genus Datisca.
Enzyme catalysisEnzyme catalysis is the increase in the rate of a process by a biological molecule, an "enzyme". Most enzymes are proteins, and most such processes are chemical reactions. Within the enzyme, generally catalysis occurs at a localized site, called the active site. Most enzymes are made predominantly of proteins, either a single protein chain or many such chains in a multi-subunit complex. Enzymes often also incorporate non-protein components, such as metal ions or specialized organic molecules known as cofactor (e.
OxideAn oxide (ˈɒksaɪd) is a chemical compound containing at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion (anion bearing a net charge of –2) of oxygen, an O2– ion with oxygen in the oxidation state of −2. Most of the Earth's crust consists of oxides. Even materials considered pure elements often develop an oxide coating. For example, aluminium foil develops a thin skin of (called a passivation layer) that protects the foil from further oxidation.
Enzyme inhibitorAn enzyme inhibitor is a molecule that binds to an enzyme and blocks its activity. Enzymes are proteins that speed up chemical reactions necessary for life, in which substrate molecules are converted into products. An enzyme facilitates a specific chemical reaction by binding the substrate to its active site, a specialized area on the enzyme that accelerates the most difficult step of the reaction.
Denitrifying bacteriaDenitrifying bacteria are a diverse group of bacteria that encompass many different phyla. This group of bacteria, together with denitrifying fungi and archaea, is capable of performing denitrification as part of the nitrogen cycle. Denitrification is performed by a variety of denitrifying bacteria that are widely distributed in soils and sediments and that use oxidized nitrogen compounds in absence of oxygen as a terminal electron acceptor. They metabolise nitrogenous compounds using various enzymes, turning nitrogen oxides back to nitrogen gas (N2) or nitrous oxide (N2O).
Nitrous-oxide reductaseIn enzymology, a nitrous oxide reductase also known as nitrogen:acceptor oxidoreductase (N2O-forming) is an enzyme that catalyzes the final step in bacterial denitrification, the reduction of nitrous oxide to dinitrogen. N2O + 2 reduced cytochome c N2 + H2O + 2 cytochrome c It plays a critical role in preventing release of a potent greenhouse gas into the atmosphere. N2O is an inorganic metabolite of the prokaryotic cell during denitrification.
Carbon dioxide in Earth's atmosphereIn Earth's atmosphere, carbon dioxide is a trace gas that plays an integral part in the greenhouse effect, carbon cycle, photosynthesis and oceanic carbon cycle. It is one of several greenhouse gases in the atmosphere of Earth. The current global average concentration of CO2 in the atmosphere is (0.04%) 421 ppm as of May 2022. This is an increase of 50% since the start of the Industrial Revolution, up from 280 ppm during the 10,000 years prior to the mid-18th century. The increase is due to human activity.
LysosomeA lysosome (ˈlaɪsəˌsoʊm) is a membrane-bound organelle found in many animal cells. They are spherical vesicles that contain hydrolytic enzymes that can break down many kinds of biomolecules. A lysosome has a specific composition, of both its membrane proteins, and its lumenal proteins. The lumen's pH (~4.5–5.0) is optimal for the enzymes involved in hydrolysis, analogous to the activity of the stomach. Besides degradation of polymers, the lysosome is involved in various cell processes, including secretion, plasma membrane repair, apoptosis, cell signaling, and energy metabolism.
École polytechniqueÉcole polytechnique, also known as Polytechnique or l'X liks, is a grande école located in Palaiseau, France. It specializes in science and engineering and is a founding member of the Polytechnic Institute of Paris. The school was founded in 1794 by mathematician Gaspard Monge during the French Revolution and was militarized under Napoleon I in 1804. It is still supervised by the French Ministry of Armed Forces. Originally located in the Latin Quarter in central Paris, the institution moved to Palaiseau in 1976, in the Paris-Saclay technology cluster.
