Geochemical Cycling Flashcards
All organisms eat at
C HOPKINS CaFe
What two elements do organisms expend the most energy trying to find?
Carbon and Nitrogen
How much of the atmosphere is made up of Carbon dioxide (CO2)
0.036% (convert to sugar during photosynthesis)
How much of the atmosphere is made up of Nitrogen (N2)
78% (have to make modifications to make it useable for organisms)
How much of the atmosphere is made up of Oxygen (O2)
21% (available to all organisms)
How much of the atmosphere is made up of Argon
0.9% (don’t really care about this one)
Biogeochemical cycling
Transitioning various chemicals between their organic an inorganic forms
Nitrogen fixation
Transitions N2 (gas) to NH4 (ammonia)
What bacteria does nitrogen fixation?
Diazotrophic (nitrogen-fixing) bacteria and archaea
Oxygenic phototrophs
Cyanobacteria
Anoxygenic phototrophs
Heliobacteria
Rhodospirillum
Chlorobium
What are some non-phototrophic nitrogen-fixing bacteria?
Symbiotic rhizobia in root nodules; mainly associated with legumes
Nitrification
NH4 (ammonia) to NO2- (nitrate) or NO3- (nitrite)
What carries out nitrification?
Autotrophic bacteria and archaea
Assimilation
NH4 (ammonia) to organic molecules
What carries out assimilation?
Plants, fungi, bacteria
Denitrification
NH4 (ammonia), NO2- (nitrate), NO3-(nitrite) to N2 (gas)
What carries out denitrification?
Wide range or, bacteria, archaea, and fungi
What is the nitrogen fixation reaction?
N2 + 8H+ + 8e- +16ATP –> 2NH3 + H2 + 16ADP + 16Pi
What enzymes carry out nitrogen fixation?
Nitrogen complex
Dihydrogen reductase and Dinitrogenase
What does dihydrogen reductase do?
Provides reducing power (e-)
What does dinitrogenase do?
Reduces the N2 (gas) in sequential steps
What are the steps to reducing N2 (gas)
N2 + H2 + 2e- –> HN=NH
HN=NH + 2H+ + 2e- –> H2N-NH2
H2N-NH2 + 2H+ + 2e- –> 2NH3
What is nitrogenase sensitive to?
Oxygen. requires a specialized environment (anaerobic)
Where are heterocysts (cyanobacteria) formed
Metabolically active cells under nitrogen-limiting conditions
What is degraded during development in heterocysts/cyanobacteria
Photosystem (no photosystem 2)
What is the purpose of heterocycts?
Dedicated to N2 fixation (eliminates reproductive potential)
What do metabolically adaptive cells (Azotbacter sp.) do?
Increase respiration rate (O2 enters but is used up rapidly)
What is the end product of nitrogen fixation?
Ammonia (NH3+)