[Environment] Role of Carbon & Nitrogen Cycles in the Environment

Carbon Cycle:

Carbon is the basic building block of the carbohydrates, fats, proteins, nucleic acids such as DNA and RNA, and other organic compounds necessary for life. Most land plants get their carbon by absorbing carbon dioxide gas, which makes up about 0.04% of the gaseous atmosphere, through pores in their leaves, Phytoplankton, the microscopic plants that float in aquatic ecosystems, get their carbon from atmospheric carbon dioxide that has dissolved in water.



These producer plants then carry out photosynthesis, which converts the carbon in carbon dioxide to carbon in complex organic compounds such as glucose:


Carbon dioxide + water + solar energy -> glucose + oxygen


Then the cells in oxygen-consuming plants, animals, and decomposers carry out aerobic cellular respiration, which breaks down glucose and other complex organic compounds and converts the carbon back to carbon dioxide for reuse by producers:

Glucose + oxygen -> carbon dioxide + water + energy

This linkage between photosynthesis and aerobic respiration circulates carbon in the ecosphere and is a major part of the carbon cycle. This part of the gaseous cycle is shown in greatly simplified in carbon cycle. And some of the ways plants, animals, and decomposers in the biosphere depend on one another for survival. Oxygen and hydrogen, the other elements in glucose and other carbohydrates, cycle almost in step with carbon.


Carbon cycles rapidly between the atmosphere and hydrosphere and living organisms it shows that some of the earth's carbon is tied up for long periods in fossil fuels-coal, petroleum, natural gas, peat, oil shale, tar sand, and lignite-formed over millions of years in the lithosphere. The carbon in these mineral deposits remains locked up until it is released to the atmosphere as carbon dioxide when fossil fuels are extracted and burned.


Nitrogen Cycle:


Organisms require nitrogen in various chemical forms to make proteins and genetically important nucleic acids such as DNA. Klost green plants need nitrogen in the form of nitrate ions (NO,-) and ammonium ions (NH4 +). The nitrogen gas (NJ that makes up about 78% of the volume of the earth's atmosphere is useless to such plants, people, and most other organisms. Fortunately, nitrogen gas is converted into water-soluble ionic compounds containing nitrate ions and ammonium ions, which are taken up by plant roots as part of the nitrogen cycle.


The conversion of atmospheric nitrogen gas into other chemical forms useful to plants is called nitrogen Fixation. It is carried out mostly by blue-green algae and certain kinds of bacteria in soil and water and by rhizobium bacteria living in small swellings called nodules on the roots of alfalfa, clover, peas, beans, and other legume plants. Also playing a role in nitrogen fixation, lightning converts nitrogen gas and oxygen gas in the atmosphere to nitric oxide and nitrogen dioxide gas. These gases react with water vapor in the atmosphere and are converted to nitrate ions that return to the earth as nitric acid dissolved in precipitation and as particles of nitrate salts.


Plants convert inorganic nitrate ions and ammonium ions obtained from soil water into proteins, DNA, and other large, nitrogen-containing organic compounds they require. Animals get most of their nitrogen-containing nutrients by eating plants or other animals that have eaten plants.

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