ch 14 Flashcards
why are redox reactions important
bc the relocation of electrons rleleases energy
reduction potential
measures the ability of a species to attract an electron and be reduced
what is the reference for reduction potentials
SHE
standard hydrogen electrode
2H+ + 2e- = H2
electrons flow from _ to _
low reductino potential to high reductino potential
if E rxn is greater than 0, K is
greater than 1
gibbs free energy
the max amount of work that can be extracted from closed system at fixed t and pressure
electron activity
the degree to whcih electrons move from one species to another
how can we find E rxn in non standard conditions
use nernst equation
use E at ph 7 bc that is the ph of water
Ehw = Eh and what
minus 0.42
PEw= pe and what
minus 7
strongest oxidizing agent in seawater
o2
all biochemically active elements in oxic seawater will be
mainly in thier highest oxidation state
the most positive they can be
the redox rxn in seawater that produces the most E is
aerobic oxidation of organics
sulfide oxidizers
bact in the ocean that are in hydrothermal vents
use O2 and H2S and form SO420 and H+
largest formatino of E
aerobic respiration of organic matter
most important source of enrgy for heterotrophs
what are some anoxic enviroments
in the gut of animals
o2 min at pycnocline
sediments
denitrification
Nitrate NO3- to N2
cant use this form of N
limits biological growth
benifit of aerobic respiration
prevents sequesteration of C in POC and returns CO2 to water and dec pH and affects climate
nitrate reduction
NO3- to NO2-
emission of nitrous oxide
potent greenhouse gas
sulfate reduction
SO42- to H2S
toxic gas
kills most organisms
low o2
dead zones
nitrogen fixation
H2 to NO3-
available N
methane fermentation
convert organic mater to CO2 and CH4
both greenhouse gasses
trap heat
iron reduction
fe3 to fe2
available and soluble form of iron
what does nitrogen fixation
done by cyanobacteria and anaerobic bacteria
what is reduced in aerobic respiration
o2
why is organic matter the most importatn reducing agent
relatively abundant
has a low pE
how is organic matter derived
directly or indirectly from biological fixation rxns where oxidized inorganic carbon CO2 is converted to reduced organic form CH2O
E source names
photo- light
chemo - organic matter
carbon source names
auto- inorganic
organo- organic carbon
electron source names
litho- inoganic e donor
hetero - organic electron donor
photoautolithotrophs example
phytoplankton that use H2O as electron source
green sulfur bact- use H2 or H2S or S as electron source
some use Fe2+
strategies of chemoautolithotrophs
archaea and bact
oxidation of hydrogen
sulfur
reduced nitrogen
reduced metals
methanogens
use H2 as source of electrons and CO2 as soruce of C and methanol as E
supersaturations of methane in surface water suggest
methanogenesis occurs in anaerobic interiors of particles
why is the production of methane important to understand
bc it is a potent greenhouse gas
mixotrophs
use both organic matter and light as energy sources
hetero and photo
mixotrophs example
phytoplankton and dinoglagellates and cyanobacteria
what are some things nobody seems to be able to do
oxidze Mn2+ and N2
anoxygenic photosynth using NH3, PH3, CH4 as e- donors
