Agriculture Reference
In-Depth Information
chapter 7
The Carbon Quandary:
Essential and Detrimental
In recent years, carbon has become a highly publicized element, mainly because
of its suspected role in global warming. But carbon is intrinsically worthy of study.
For starters, carbon has four electrons in its outermost shell, so it is likely to share
four to fill its outermost shell. This means that it readily forms covalent bonds
and is the main reason that so many organic compounds are possible. Carbon
also forms polymers (linked chemical units) readily at ambient temperatures and
pressures found on Earth, requiring no super heating. These include cellulose,
lignins, and other polymers that are abundant in plant and animal tissues. Carbon
is also the basis of synthetic polymers, which are common in almost every aspect
of contemporary life and provide the potential for sustainable solution to many
of the greatest challenges as new materials are formed from composites (needed
in health care, industry, clothing, etc.)
Living systems both reduce and oxidize carbon. Reduction is the act of gaining
electrons, whereas oxidation is the act of losing electrons from the outermost shell.
Reduction often takes place in the absence of molecular oxygen (O 2 ), such as in
the rumen of cattle, in sludge at the bottom of a lagoon, or in buried detritus on
the forest floor. Anaerobic bacteria get their energy by reduction, breaking down
organic compounds into methane (CH 4 ) and water.
Conversely, aerobic microbes get their energy from oxidation, forming carbon
dioxide (CO 2 ) and water. Plants absorb CO 2 for photosynthesis, the process by
which plants convert solar energy into biomass and release O 2 as a by-product.
Thus, the essential oxygen is actually the waste product of photosynthesis and is
derived from carbon-based compounds. Respiration generates carbon dioxide as
a waste product of oxidation that takes place in organisms, so there is a balance
between green plants' uptake of CO 2 and release of O 2 in photosynthesis and the
uptake of O 2 and release of CO 2 in respiration by animals, microbes, and other
organisms.
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