Nitrogen, symbolized as N, is a nonmetallic element found across the universe, estimated to be the seventh most abundant in the Milky Way and our Solar System. On Earth, nitrogen is particularly plentiful, making up approximately 78% of the atmosphere as a colorless, odorless gas (N₂). Its widespread presence and unique chemical properties make it an indispensable component in natural systems and human-made applications.
Nitrogen in Living Organisms
Nitrogen is an indispensable component of all living organisms, forming the structural backbone of biological molecules. It is a fundamental part of amino acids, the building blocks of proteins. Proteins carry out functions within cells, including forming structural components, acting as enzymes, transporting molecules, and regulating cellular processes.
Beyond proteins, nitrogen is a key constituent of nucleic acids, DNA and RNA. These molecules store and transmit genetic information. The nitrogenous bases—adenine, guanine, cytosine, and thymine (or uracil in RNA)—are the informational units of these nucleic acids, determining the genetic code.
In plants, nitrogen plays a direct role in photosynthesis through its presence in chlorophyll. This green pigment captures light energy from the sun and contains nitrogen atoms. Without sufficient nitrogen, plants cannot produce enough chlorophyll, hindering their ability to perform photosynthesis and grow.
Nitrogen also contributes to other biomolecules, such as adenosine triphosphate (ATP), the primary energy currency of the cell. The adenine component of ATP contains nitrogen. Nitrogen is also found in the chemical structures of various vitamins, organic compounds required for proper metabolic function.
Nitrogen in Earth’s Systems
Nitrogen cycles continuously through Earth’s environmental systems, transitioning between different forms. The atmosphere represents the largest reservoir, containing approximately 78% of atmospheric gases as dinitrogen (N₂). This atmospheric nitrogen is largely inert and not directly usable by most living organisms.
In soil, nitrogen exists in forms including nitrates (NO₃⁻), nitrites (NO₂⁻), and ammonium (NH₄⁺). These reactive forms are crucial for plant uptake and growth. Specialized microorganisms convert atmospheric nitrogen into usable forms through nitrogen fixation, making it available to plants.
Nitrogen compounds are also present in aquatic environments like oceans, lakes, and rivers. Dissolved nitrates, nitrites, and ammonia contribute to the nutrient balance of these ecosystems, supporting aquatic plants and microorganisms. The movement of nitrogen within water bodies influences aquatic food webs and ecosystem health.
The nitrogen cycle describes the pathways through which nitrogen moves between the atmosphere, soil, water, and living organisms. This cycle involves processes like nitrogen fixation, nitrification (conversion of ammonium to nitrites and nitrates), denitrification (conversion of nitrates back to atmospheric nitrogen), and ammonification (decomposition of organic nitrogen into ammonia). These transformations ensure the continuous availability of nitrogen for biological and geological processes.
Nitrogen in Everyday Products and Industries
Nitrogen’s diverse chemical properties make it valuable in numerous human-made products and industrial applications. One widespread use is in agricultural fertilizers, where it is a primary nutrient for enhancing crop yield. Forms like ammonia, urea, and ammonium nitrate are commonly applied to supply plants with the nitrogen they need for growth.
Nitrogen compounds are integral to the manufacturing of explosives. For instance, nitroglycerin and trinitrotoluene (TNT) contain nitrogen, as does ammonium nitrate, which can be used in some explosive mixtures. The high energy within the nitrogen-nitrogen bonds in these compounds contributes to their explosive properties.
In synthetic materials, nitrogen is a component in certain plastics and fibers. Nylon, for example, is a polyamide, meaning its repeating units contain nitrogen atoms. This incorporation contributes to the strength and versatility of these materials.
Many pharmaceutical drugs include nitrogen as part of their molecular structure. Nitrogen-containing functional groups are common in medicinal chemistry, influencing the drug’s activity and interaction with biological targets. This makes nitrogen a frequent element in new medication development.
Liquid nitrogen, cooled to an extremely low temperature, serves as a refrigerant and is used in cryopreservation. Its very low boiling point makes it effective for freezing biological samples, food products, and industrial cooling. Nitrogen gas is often employed as an inert atmosphere in food packaging to preserve freshness by displacing oxygen.