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Carbon, an element discovered before history itself, is one of the most
abundant elements in the universe. It can be found in the sun, the stars,
comets, and the atmospheres of most planets. There are close to ten million
known carbon compounds, many thousands of which are vital to the basis of life
itself (WWW 1).
Carbon occurs in many forms in nature. One of its purest forms is diamond.
Diamond is the hardest substance known on earth. Although diamonds found in
nature are colorless and transparent, when combined with other elements its
color can range from pastels to black. Diamond is a poor conductor of heat and
electricity. Until 1955 the only sources of diamond were found in deposits of
volcanic origin. Since then scientists have found ways to make diamond from
graphite and other synthetic materials. Diamonds of true gem quality are not
made in this way (Beggott 3-4).
Graphite is another form of carbon. It occurs as a mineral in nature, but it
can be made artificially from amorphous carbon. One of the main uses for
graphite is for its lubricating qualities. Another is for the "lead" in
pencils. Graphite is used as a heat resistant material and an electricity
conductor. It is also used in nuclear reactors as a lubricator (Kinoshita
119-127). Amorphous carbon is a deep black powder that occurs in nature as a
component of coal. It may be obtained artificially from almost any organic
substance by heating the substance to very high temperatures without air.
Using this method, coke is produced from coal, and charcoal is produced from
wood. Amorphous carbon is the most reactive form of carbon. Because amorphous
carbon burns easily in air, it is used as a combustion fuel. The most
important uses for amorphous carbon are as a filler for rubber and as a black
pigment in paint (WWW 2).
There are two kinds of carbon compounds. The first is inorganic. Inorganic
compounds are binary compounds of carbon with metals or metal carbides. They
have properties ranging from reactive and saltlike; found in metals such as
sodium, magnesium, and aluminum, to an unreactive and metallic, such as
titanium and niobium (Beggott 4).
Carbon compounds containing nonmetals are usually gases or liquids with low
boiling points. Carbon monoxide, a gas, is odorless, colorless, and tasteless.
It forms during the incomplete combustion of carbon (Kinoshita 215-223). It is
highly toxic to animals because it inhibits the transport of oxygen in the
blood by hemoglobin (WWW 2). Carbon dioxide is a colorless, almost odorless
gas that is formed by the combustion of carbon. It is a product that results
from respiration in most living organisms and is used by plants as a source of
carbon. Frozen carbon dioxide, known as dry ice, is used as a refrigerant.
Fluorocarbons, such as Freon, are used as refrigerants (Kinoshita 225-226).
Organic compounds are those compounds that occur in nature. The simplest
organic compounds consist of only carbon and hydrogen, the hydrocarbons. The
state of matter for organic compounds depends on how many carbons are
contained in it. If a compound has up to four carbons it is a gas, if it has
up to 20 carbons it is a liquid, and if it has more than 20 carbons it is a
solid (Kinoshita 230-237).
The carbon cycle is the system of biological and chemical processes that make
carbon available to living things for use in tissue building and energy
release (Kinoshita 242). All living cells are composed of proteins consisting
of carbon, hydrogen, oxygen, and nitrogen in various combinations, and each
living organism puts these elements together according to its own genetic
code. To do this the organism must have these available in special compounds
built around carbon. These special compounds are produced only by plants, by
the process of photosynthesis. Photosynthesis is a process in which
chlorophyll traps and uses energy from the sun in the form of light. Six
molecules of carbon dioxide combine with six molecules of water to form one
molecule of glucose (sugar). The glucose molecule consists of six atoms of
carbon, twelve of hydrogen, and six of oxygen. Six oxygen molecules,
consisting of two oxygen atoms each, are also produced and are discharged into
the atmosphere unless the plant needs energy to live. In that case, the oxygen
combines with the glucose immediately, releasing six molecules of carbon
dioxide and six of water for each molecule of glucose (Beggott 25-32). The
carbon cycle is then completed as the plant obtains the energy that was stored
by the glucose. The length of time required to complete the cycle varies. In
plants without an immediate need for energy, the chemical processes continue
in a variety of ways. By reducing the hydrogen and oxygen content of most of
the sugar molecules by one water molecule and combining them to form large
molecules, plants produce substances such as starch, inulin , and fats and
store them for future use. Regardless of whether the stored food is used later
by the plant or consumed by some other organism, the molecules will ultimately
be digested and oxidized, and carbon dioxide and water will be discharged.
Other molecules of sugar undergo a series of chemical changes and are finally
combined with nitrogen compounds to form protein substances, which are then
used to build tissues (WWW 2).
Although protein substances may pass from organism to organism, eventually
these too are oxidized and form carbon dioxide and water as cells wear out and
are broken down, or as the organisms die. In either case, a new set of
organisms, ranging from fungi to the large scavengers, use the waste products
or tissues for food, digesting and oxidizing the substances for energy release
(WWW 1).
At various times in the Earth’s history, some plant and animal tissues have
been protected by erosion and sedimentation from the natural agents of
decomposition and converted into substances such as peat, lignite, petroleum,
and coal. The carbon cycle, temporarily interrupted in this manner, is
completed as fuels are burned, and carbon dioxide and water are again added to
the atmosphere for reuse by living things, and the solar energy stored by
photosynthesis ages ago is released (Kinoshita 273-275).
Almost everything around us today has some connection with carbon or a carbon
compound. Carbon is in every living organism. Without carbon life would not
exist as we know it.
Science Essays
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