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Kimberly Pambid
1st period
AP Biology
10/30/09
Free Response: Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a
member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four
electrons available to form covalent chemical bonds. Carbon is the 15th most abundant
elements in the Earth's crust, and the fourth most abundant element in the universe by
mass after hydrogen, helium, and oxygen. It is present in all known lifeforms, and in the
human body carbon is the second most abundant element by mass after oxygen. This
abundance, together with the unique diversity of organic compounds and their unusual
polymer-forming ability at the temperatures commonly encountered on Earth, make this
element the chemical basis of all known life. It has an affinity for bonding with other
small atoms, including other carbon atoms, and is capable of forming multiple stable
covalent bonds with such atoms. As a result, carbon is known to form almost ten million
different compounds; the large majority of all chemical compounds. Carbon also has the
highest melting and sublimation point of all elements. Although it forms an extraordinary
variety of compounds, most forms of carbon are comparatively unreactive under normal
conditions. Carbon is present in the atmosphere as carbon dioxide in 0,03% in volume.
Several minerals, like limestone, dolomite, gypsum and marble, contain carbonates. All
the plants and live animals are formed by complex organic compounds where carbon is
combined with hydrogen, oxygen, nitrogen and other elements. The remains of live
plants and animals form deposits: of petroleum, asphalt and bitumen. The natural gas
deposits contain compounds formed by carbon and hydrogen.
In combination with oxygen in carbon dioxide, carbon is found in the Earth's
atmosphere and dissolved in all water bodies. Hydrocarbons contain carbon as well—coal
"reserves". With smaller amounts of calcium, magnesium, and iron, carbon is a major
component in very large masses of carbonate rock. Carbon occurs in all known organic
life and is the basis of organic chemistry. When united with hydrogen, it forms various
flammable compounds called hydrocarbons which are important to industry as
refrigerants, lubricants, solvents, as chemical feedstock for the manufacture of plastics
and petrochemicals and as fossil fuels. When combined with oxygen and hydrogen,
carbon can form many groups of important biological compounds including sugars,
lignans, chitins, alcohols, fats, and aromatic esters. With nitrogen it forms alkaloids, and
with the addition of sulfur also it forms antibiotics, amino acids, and rubber products.
With the addition of phosphorus to these other elements, it forms DNA and RNA, the
chemical-code carriers of life, and adenosine triphosphate (ATP), the most important
energy-transfer molecule in all living cells.
The most prominent oxide is carbon dioxide. This was once the principal
constituent of the paleoatmosphere, but is a minor component of the Earth's atmosphere
today. Dissolved in water, it forms carbonic acid, but as most compounds with multiple
single-bonded oxygens on a single carbon it is unstable. Through this intermediate,
though, resonance-stabilized carbonate ions are produced. Some important minerals are
carbonates, notably calcite. Carbon disulfide is similar. The other common oxide is
carbon monoxide. It is formed by incomplete combustion, and is a colorless, odorless
gas. The molecules each contain a triple bond and are fairly polar, resulting in a tendency
to bind permanently to hemoglobin molecules, displacing oxygen, which has a lower
binding affinity. Too much carbon dioxide in the atmosphere results in the greenhouse
effect, which is the heating of the surface of a planet or moon due to the presence of an
atmosphere containing gases that absorb and emit infrared radiation. Thus, greenhouse
gases trap heat within the surface-troposphere system. This mechanism is fundamentally
different from that of an actual greenhouse, which works by isolating warm air inside the
structure so that heat is not lost by convection. Carbon dioxide is the human-produced
greenhouse gas that contributes most of radioactive forcing from human activity. CO2 is
produced by fossil fuel burning and other human activities such as cement production and
tropical deforestation. The effect of combustion-produced carbon dioxide on the global
climate, a special case of the greenhouse effect.
A carboxyl group is a set of four atoms bonded together and present in carboxylic
acids, including amino acids. Straight chain mono- and dicarboxylic acids occur in many
natural settings and many are produced industrially on a large scale. They are used in the
production of polymers, pharmaceuticals, solvent, and food additives. Vinegar, a dilute
solution of acetic acid, is biologically produced from the fermentation of ethanol. It is
used in food and beverages, but is not used in industry. Important carboxylic acids
include acrylic and methacrylic acids which are used in polymer synthesis, adipic acid,
citric acid, fatty acids, maleic acid (polymers), propionic acid (food preservative),
terephthalic acid (polymers), and amino acids which are the building blocks of proteins
that is important to the structure and function of living organisms. Carboxylic acids are
also found in nutritional supplements used by humans. All fats consist of fatty acids
bonded to a backbone structure, often glycerol. Chemically, this is a triester of glycerol,
an ester being the molecule formed from the reaction of the carboxylic acid and an
organic alcohol. Fats play a vital role in maintaining healthy skin and hair, insulating
body organs against shock, maintaining body temperature, and promoting healthy cell
function. Fats also serve as energy stores for the body, containing about. They are broken
down in the body to release glycerol and free fatty acids. The glycerol can be converted
to glucose by the liver and thus used as a source of energy. Fat also serves as a useful
buffer towards a host of diseases. When a particular substance, whether chemical or
biotic—reaches unsafe levels in the bloodstream, the body can effectively dilute—or at
least maintain equilibrium of—the offending substances by storing it in new fat tissue.
This helps to protect vital organs, until such time as the offending substances can be
metabolized and/or removed from the body by such means as excretion, urination,
accidental or intentional bloodletting, sebum excretion, and hair growth.
While it is nearly impossible to remove fat completely from the diet, it would be
unhealthy to do so. Some fatty acids are essential nutrients, meaning that they can't be
produced in the body from other compounds and need to be consumed in small amounts.
All other fats required by the body are non-essential and can be produced in the body
from other compounds.