ch 14

Question 1

why are redox reactions important

Answer 1

bc the relocation of electrons rleleases energy

Question 2

reduction potential

Answer 2

measures the ability of a species to attract an electron and be reduced

Question 3

what is the reference for reduction potentials

Answer 3

SHE
standard hydrogen electrode

2H+ + 2e- = H2

Question 4

electrons flow from _ to _

Answer 4

low reductino potential to high reductino potential

Question 5

if E rxn is greater than 0, K is

Answer 5

greater than 1

Question 6

gibbs free energy

Answer 6

the max amount of work that can be extracted from closed system at fixed t and pressure

Question 7

electron activity

Answer 7

the degree to whcih electrons move from one species to another

Question 8

how can we find E rxn in non standard conditions

Answer 8

use nernst equation

use E at ph 7 bc that is the ph of water

Question 9

Ehw = Eh and what

Answer 9

minus 0.42

Question 10

PEw= pe and what

Answer 10

minus 7

Question 11

strongest oxidizing agent in seawater

Answer 11

o2

Question 12

all biochemically active elements in oxic seawater will be

Answer 12

mainly in thier highest oxidation state

the most positive they can be

Question 13

the redox rxn in seawater that produces the most E is

Answer 13

aerobic oxidation of organics

Question 14

sulfide oxidizers

Answer 14

bact in the ocean that are in hydrothermal vents

use O2 and H2S and form SO420 and H+

Question 15

largest formatino of E

Answer 15

aerobic respiration of organic matter

most important source of enrgy for heterotrophs

Question 16

what are some anoxic enviroments

Answer 16

in the gut of animals

o2 min at pycnocline

sediments

Question 17

denitrification

Answer 17

Nitrate NO3- to N2

cant use this form of N
limits biological growth

Question 18

benifit of aerobic respiration

Answer 18

prevents sequesteration of C in POC and returns CO2 to water and dec pH and affects climate

Question 19

nitrate reduction

Answer 19

NO3- to NO2-

emission of nitrous oxide

potent greenhouse gas

Question 20

sulfate reduction

Answer 20

SO42- to H2S

toxic gas
kills most organisms
low o2
dead zones

Question 20

nitrogen fixation

Answer 20

H2 to NO3-

available N

Question 20

methane fermentation

Answer 20

convert organic mater to CO2 and CH4

both greenhouse gasses
trap heat

Question 20

iron reduction

Answer 20

fe3 to fe2

available and soluble form of iron

Question 21

what does nitrogen fixation

Answer 21

done by cyanobacteria and anaerobic bacteria

Question 22

what is reduced in aerobic respiration

Answer 22

o2

Question 23

why is organic matter the most importatn reducing agent

Answer 23

relatively abundant

has a low pE

Question 24

how is organic matter derived

Answer 24

directly or indirectly from biological fixation rxns where oxidized inorganic carbon CO2 is converted to reduced organic form CH2O

Question 25

E source names

Answer 25

photo- light
chemo - organic matter

Question 26

carbon source names

Answer 26

auto- inorganic
organo- organic carbon

Question 27

electron source names

Answer 27

litho- inoganic e donor
hetero - organic electron donor

Question 28

photoautolithotrophs example

Answer 28

phytoplankton that use H2O as electron source

green sulfur bact- use H2 or H2S or S as electron source

some use Fe2+

Question 29

strategies of chemoautolithotrophs

Answer 29

archaea and bact

oxidation of hydrogen
sulfur
reduced nitrogen
reduced metals

Question 30

methanogens

Answer 30

use H2 as source of electrons and CO2 as soruce of C and methanol as E

Question 31

supersaturations of methane in surface water suggest

Answer 31

methanogenesis occurs in anaerobic interiors of particles

Question 32

why is the production of methane important to understand

Answer 32

bc it is a potent greenhouse gas

Question 33

mixotrophs

Answer 33

use both organic matter and light as energy sources

hetero and photo

Question 34

mixotrophs example

Answer 34

phytoplankton and dinoglagellates and cyanobacteria

Question 35

what are some things nobody seems to be able to do

Answer 35

oxidze Mn2+ and N2

anoxygenic photosynth using NH3, PH3, CH4 as e- donors