C cycling

Question 1

Biogeochemical Cycling

Answer 1

production and degradation of biomass, all biomass elements have similar proportion, done through changes in oxidization state

Question 2

Carbon cycle (land)

Answer 2

-land: major site of O2 fixation, soil humus (bulk of land C), v. slowly biodegraded

Question 3

Carbon cycle (atmospheric)

Answer 3

rapidly cycling

Question 4

Carbon cycle (oceans/other waters)

Answer 4

site of CO2 fixation, organic matter decomposition, less influence than land resevoir

Question 5

Carbon cycle (sediments/rock)

Answer 5

largest resevoir of C (99.5%), extremely long turnover time

Question 6

CO2 fixation

Answer 6

mostly through photosynthesis and little through chemosynthesis
-primary production:
1)oxygenic photosynthesis: higher plants, eukaryotic microalgae, cyanobacteria
-light>
CO2 + H2O [CH2O] + O2

2)anoxygenic photosynthesis: e.g., purple sulphur, green sulphur bacteria
-light>
CO2 + H2S [CH2O] + S

Question 7

Respiration

Answer 7

occurs in dark and light by organotrophs, phototrophs, lithotrophs
[CH2O] + O2 -> CO2 + H2O
-decomposition of organic matter: catabolic, energy yeilding rxns carried out by organotrophs
-photosynthetically fixed C is eventually remineralized to CO2, CH4
-photosynthesis over respiration rate = net biomass production

Question 8

Methanotrophs

Answer 8

specialize in 1C metabolism (CH4->CO2+cells)

• methane monooxygenase catalyzes methane to methanol
• often microaerophilic

Question 9

Aerobic methanotrophs

Answer 9

live where the gradients of oxygen and methane overlap - the oxic/anoxic interface

Question 10

Anoxic decomposition

Answer 10

1) hydrolysis of polymers
2) primary fermentations
3) secondary fermentaitons, H2 producing, fatty acid-oxidizing syntrophs)
4) H2 consumption by methanogenesis and acetogenesis

Question 11

Syntrophs

Answer 11

• substrates come from sugars, amino acids, FA fermentation
• provides substrate for methanogens and homoacetogens - maintains low H2 levels
• is interspecies H2 transfer (from syntroph to methanogen), produce H2, then use H2

Question 12

Examples of anoxic conversion reactions

Answer 12

1) fermentation
2) syntrophic rxns, interspecies H2 transfer
3) acetotrophic methanogenesis
4) acetogenesis from H2,CO2

Question 13

Rumen: Methanogenic Ecosystem

Answer 13

Ruminants eat plant material but rely on methanogens to proceses the fatty acids and be absorbed into the bloodstream for oxidation

Question 14

methane budget

Answer 14

methane is 30x more potent than CO2 (more abundant in atmosphere)