The Earth’s atmosphere consists of a stratified layer of gases that are held in place due to gravity. The major constituents of atmospheric air are nitrogen, oxygen, argon and carbon dioxide. Nitrogen and carbon dioxide are both essential to life on Earth and are vital for a number of biochemical processes such as photosynthesis and protein synthesis.
Chemical and Physical Properties of Nitrogen
Nitrogen is an element in the periodic table with an atomic number of 7. Nitrogen's nucleus consists of 7 protons with a positive charge, and usually 7 neutrons with zero charge. In order to maintain an electrically neutral atom, 7 electrons orbit the nucleus in a series of shells. Nitrogen is a gas at room temperature and makes up about 78 percent of the Earth's atmosphere. Nitrogen liquefies at -210.1 degrees Celsius (-346.18 degrees Fahrenheit), which allows for its use in cryogenic experiments and activities.
Chemical and Physical Properties of Carbon Dioxide
Carbon dioxide is a compound with a molecule consisting of a single carbon atom and two oxygen atoms. Electrons in the outer shell of the carbon and oxygen atoms are shared to form covalent bonds. Carbon dioxide is a gas at room temperature and makes up 0.03 percent of the Earth's atmosphere. Carbon dioxide is unusual in that it forms a solid without passing through a liquid phase at normal atmospheric pressure. This process is known as sublimation. Carbon dioxide sublimes to form dry ice at a temperature of -56 degrees Celsius (-68.8 degrees Fahrenheit).
Role of Carbon dioxide in Biological Processes
Photosynthesis, the process by which plants convert sunlight into glucose sugar, constitutes one of the most fundamental biological reactions that takes place on Earth and forms the basis of life at the bottom of the food chain, providing more complex organisms, such as mammals, with a supply of food. Photosynthesis requires a natural source of carbon in order to synthesize glucose; it obtains this from atmospheric carbon dioxide gas. The chemical word equation for photosynthesis is:
Carbon dioxide + Water (With Sunlight and Chlorophyll) = Glucose + Oxygen
Role of Nitrogen Gas in Biological Processes and the Nitrogen Cycle
Nitrogen is an essential building block of fundamental biological molecules, such as proteins and nucleic acids. Nitrogen gas from the atmosphere is captured by "nitrogen-fixing" bacteria. During this process, nitrogen and hydrogen gases are converted into ammonia that plants can absorb directly. Alternatively, ammonia decays in the soil into nitrates that plants also can absorb. Plants use ammonia and nitrates to synthesize biochemical molecules, such as chlorophyll, proteins and nucleic acids. Nitrogen can be released back into the atmosphere via a number of processes. Denitrifying bacteria that live in soil can convert nitrates into nitrogen gas. Alternatively, nitrogen-containing molecules within plants are consumed by animals, resulting in nitrogen-rich excrement. Nitrifying bacteria break down the ammonia in this waste, converting it to nitrates. Denitrrifying bacteria then break down those nitrates to nitrogen gas. These steps form the basis of the nitrogen cycle.
About the Author
Samuel Markings has been writing for scientific publications for more than 10 years, and has published articles in journals such as "Nature." He is an expert in solid-state physics, and during the day is a researcher at a Russell Group U.K. university.