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I need help with a practice exam. I attached a document with questions I need help with. If you can show your work and explain, I would greatly appreciate it!
Geomicrobiology
Please provide a response to each of the questions below. Responses must be typed.
Question #2 requires a simple illustration that you can produce electronically or draw by
hand (preferably by hand if your handwriting is neat).
1) Please explain the significance and implications of the “Vernadsky Paradox” from a
microbial perspective.
2)
a) Illustrate an organic contaminant (e.g. benzene) plume that is entering a previously
uncontaminated aquifer from a point source (e.g. a leaking underground storage tank),
and show the predominant terminal electron accepting processes that you would expect to
be occurring at different regions of that contaminant plume
. b) “Defend” this by determining the thermodynamic favorability of these different
terminal electron accepting processes, assuming the potential terminal electron accepting
processes would be aerobic respiration (O2 reduction), Mn(IV) (pyrolusite) reduction (to
Mn2+), Fe(III) (ferrihydrite) reduction (to Fe2+), sulfate reduction (so sulfide), and
methanogenesis. Before calculating the energetic favorability of these processes, produce
balanced reactions depicting these terminal electron accepting processes based on H2 as
the electron donor (be sure to normalize all reactions on the basis of one mole of H2).
c) Explain how the thermodynamic favorability of the different terminal electron
accepting processes. A table that includes ∆G0f related to this question is provided at the
end of the exam.
d) Why might it be “scientifically defensible” to use H2 for these calculations, and not
benzene?
3) What ways do we classify microorganisms? What are strengths and weaknesses to the
approaches, and why are they strengths/weaknesses?
4) What are approaches we use to understand “who’s there and what are they doing?”
from a microbial perspective. Discuss the strengths and weaknesses of these approaches.
5) Explain the similarities and differences between phototrophy and chemotrophy.
6) Given the requirements for life, how might microbial communities be sustained in the
absence of solar energy (please include examples)?
Selected ∆G0f
Chemical species
Mn2+
MnO2 (pyrolysite)
H2
H+
H2O
S0 (elemental sulfur)
HS- (sulfide)
SO42- (sulfate)
Fe(OH)3 (ferrihydrite)
Fe2+
CO2
CH4
O2
∆G0f
-228 kJ/mol
-457 kJ/mol
0 kJ/mol
-40 kJ/mol (@ pH 7)
-237 kJ/mol
0
+12 kJ/mol
-744 kJ/mol
-692 kJ/mol
-83 kJ/mol
-397 kJ/mol
-34 kJ/mol
16.4 kJ/mol
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