1.
Microbial
exudates (other than enzymes) can create a micro-environment in which certain
polymers become chemically unstable. For example, sulfur bacteria produce
sulfuric acid from sulfide or sulfur. Many fungi secrete organic acids while
decomposing plant materials, while plant roots secrete both H+ and HCO3 -
during the uptake of nutrients. Explain briefly how the above processes can
influence polymer degradation.
Answer
If
these processes occur in the vicinity of acid - or base - susceptible polymers,
they may increase the degradation rates of the polymers.
2.
Degradation
of all polymers follows a sequence in which the polymer is first converted to
its monomers, after which the monomers are mineralized. Why is it necessary for
the conversion of the polymer to monomers interms of the polymer degradation
within microbial cells.
Answer
Most
polymers are too large to pass through cellular membranes, so they must first
be depolymerized to small monomers before they can be absorbed and biodegraded
within microbial cells.
3.
Explain
briefly the following i) Abiotic hydrolysis ii) Abiotic oxidation of polymer
degradation, Specifying the type of polymer (give at least two examples)
natural or synthetic been degraded under each of the processes.
Answer
i)
Abiotic hydrolysis is the most important
reaction for initiating the environmental degradation of synthetic polymers,
hydrolysis acts as the initial step of splitting the polymer into its monomers,
after which the monomers can be biodegraded.
Examples include polycarboxylates, polylactic
acids and silicones.
ii)
Abiotic oxidation can also
initiate the degradation of some polymers. For example, polyethylene undergoes an auto-oxidation, which
gradually reduces its molecular weight to the point where biodegradation can proceed.
Air pollutants such as ozone, nitric oxides and sulfuric oxides may also
promote abiotic oxidation of polymers. Finally, sunlight which strikes the
surface of many polymers will be absorbed, oxidizing the materials and thus
beginning their degradation abiotically.
4.
State
the conditions under which i) soil microorganisms to rapidly degrade cellulose
and starch ii) fungi degrade wood
Answer
i)
A ready supply of nutrients,
oxygen, and water are needed for soil microorganisms to rapidly degrade
cellulose and starch.
ii)
Fungi which degrade wood are
actually more active under poor nutrient conditions.
5.
Explain
in detail the natural degradation of silicon.
Answer
Degradation
of silicon follows a sequence in which the polymer is first converted to its
monomers, after which the monomers are mineralized, in that it begins with an
abiotic hydrolysis of the large polymer to small, water soluble monomers.
The
monomer is then either biodegraded by soil microorganisms, the speed of
degradation depends on the specific environmental conditions. For example, a
ready supply of nutrients, oxygen, and water are needed for soil microorganisms
to rapidly degrade, or it evaporates from the soil and should oxidize in the
presence of sunlight. The cycle is thus completed: silicone, which is made from
pure quartz sand, is eventually returned to the earth as soil silicates.
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