chapter 21 - nutrient cycles

Question 1

What is the carbon cycle?

Answer 1

cycling carbon through all earths major carbon reservoirs

Question 2

Reservoirs

Answer 2

rocks+sediments, oceans, methane hydrates, fossil fuels

Question 3

How does the carbon-removal cycle work?

Answer 3

CO2 in atmosphere is transferred carbon reservoir, with the help of photosynthetic land plants and marine microbes

Question 4

Carbonturnover

Answer 4

CO2 is returned through respiration and decomposition

Question 5

What is the largest source of CO2?

Answer 5

microbial decomposition

Question 6

What has increased atmospheric carbon by 40%

Answer 6

humans

Question 7

What are some oxygenic phototropic organisms?

Answer 7

1. plants (terrestrial)
2. microorganisms ( aquatic)

Question 8

Photosynthesis

Answer 8

• reduces inorganic CO2 to organic CH2O
  CO2 + H2O = CH2O + O2

Question 9

Respiration

Answer 9

• oxidizes organic CH2O to inorganic CO2
  CH2O + O2 = CO2 + H2O

Question 10

What are the end products of decomposition

Answer 10

1. methane (CH4): greenhouse gas, produced in oxygen free environments
2. carbon dioxide (CO2): methane converted to CO2 by methanotrophs
3. methane hydrates: when high levels of methane are under high pressure + low temperature

Question 11

Example of a coupled cycle

Answer 11

carbon cycle and nitrogen cycle are closely coupled

Question 12

Methanogenesis

Answer 12

central to carbon cycling in anoxic environments.

Question 13

Methanogenesis mechanism

Answer 13

methanogens use CO2 as terminal electron acceptor, reducing CO2 to CH4 with H2 as electron donor
Acetate is always being formed from monomers.

Question 14

Acetogenesis

Answer 14

H2 - consuming process that competes with methanogenesis, but is less favourable

Question 15

Nitrogen fixation

Answer 15

reduces N2 + 8H = 2NH3 + H2

Question 16

Denitrification

Answer 16

reduces nitrate to gaseous nitrogen
- NO3- = N2/NO

Question 17

Ammonification

Answer 17

no redox change
- decomposition of organic nitrogen compounds to NH3

Question 18

Dissimulative nitrate reduction to ammonia (DNRA)

Answer 18

reduction
- pathway used by nitrate- reducing bacteria ( NO3- or NO2- to NH3

Question 19

Nitrification

Answer 19

oxidation
- oxidize NH3 to NO2-
- then oxidizes NO2- to NO3-

Question 20

Comammox

Answer 20

oxidation
- oxidize NH3 to NO3-

Question 21

Anammox

Answer 21

oxidation and reduction
- NH3 is oxidized with NO2- anaerobically to N2

Question 22

Assmiliation

Answer 22

1. Reduction : NO3- to NH2 groups of proteins
2. No redox change: NH3 to NH2

Question 23

How is mercury in the enviornment?

Answer 23

Hgº is the elementary mercury that gets oxidized to Hg2+ then enters aquatic environments.

Question 24

How is Hg2+ modified by microorganisms?

Answer 24

1. sulfate reducing bacteria (HgS)
2. specific enzymes are involved in methylation of mercury
3. methylmercury is toxic (CH3Hg+)

Question 25

Organomercury lyase

Answer 25

cleaves CH3HG+ to CH4 and Hg2+
then reduced by mercutic reductase to Hgº

Question 26

What is the mercury resistance mechanism

Answer 26

MerP in periplasm binds Hg2+ and transfers it to MerT then interacts with mercuric reductase MerA to reduce Hg2+ to Hgº
Hgº is volatile and nonpolar and so it exits through cytoplasmic membrane.

Question 27

Radiative forcing

Answer 27

entire planet feels like greenhouse

Question 28

What are the major sources of methane emissions

Answer 28

atmospheric methane account for 20% of increased radioactive forcing
- fossil fuels
- wetlands
- plants
- biomass burning

Question 29

Human impact of nitrogen cycle

Answer 29

humans produce lots of nitrogenous fertilizers like CO4, CH4, N2O (greenhouse gas emissions