Lecture 1 - Exam 5 Flashcards
What organisms depend on nitrogen?
It is required in large amounts as an essential component of?
All organisms.
Required in large amounts as an essential component of proteins, nucleic acids, and other cell constituents. It is critical for agricultural production.
Is N2 available for use by most organisms?
Why?
It is unavailable for use by most organisms because there is a triple bond between the two nitrogen atoms, making the molecule almost inert.
What is often the limiting factor for growth and biomass production in all environments where there is suitable climate and availability of water to support life?
Nitrogen.
In order for nitrogen to be used for growth, what must happen?
It must be fixed in the form of ammonium (NH4)*
What does the overuse of ammonia as plant fertilizer result in?
Contaminated ground water, leading to eutrophication.
Increases in nutrient availability results in blooms of algae and cyanobacteria.
N is cycled between:
NH4+ (ammonia, -3 oxidation state) and NO3- (nitrate, +5 oxidation state)
What kind of organisms are critical for nitrogen cycling?
What are these specific processes?
Prokaryotes.
Nitrogen fixation, nitrification, denitrification, ammonification (through biomass decomposition).
Fixing nitrogen is difficult because?
Of the strength of the N2 bond (triple bond).
-Reduction of N2 to NH3 requires a lot of energy to break the triple N2 bond (16 ATP to fix 1 N2 to make 2 NH3).
Nitrogen fixation is critical for agriculture. What’s the deal with plants?
Plants cannot use N2 directly but need N in a usable form like ammonia (NH3).
What is the method for nitrogen fixation?
Haber-Bosch method: ammonia production using catalyst with H2 and N2 at 200 atm and 500 C have negative environmental effect.
-More than 100 million tons of NH3 produced annually via Haber-Bosch method.
More NH3 produced by ________ than Haber-Bosch method (~400 million tons/yr).
Bacteria
Nitrogen fixation is confined to? What kind of organisms cannot fix nitrogen?
Confined to prokaryotes. Eukaryotic species cannot fix nitrogen.
What kind of prokaryotes can fix nitrogen?
Prokaryotes and Archaea
-Symbiotic and free-living
-Aerobic and anaerobic
Where were nitrogen-fixing bacteria first found?
In the nodules of clover roots.
Formation of a root nodule in a legume infected by Rhizobium requires what?
In order to initiate a productive symbiosis, rhizobia must..?
Molecular communication to establish infection.
Rhizobia must recognize and then respond to the presence of host plant roots.
What are the steps for the formation of the nodule?
- Plant roots produce flavonoid compounds.
- Rhizobium cells respond by producing nodulation (nod) factors.
- In response to nod factors, plant roots grow root hairs. Rhizobium infects and grows within the root hair.
- Bacteria in infection thread form a ‘bacteroid’ elongated cell type as they penetrate the root.
- The infected root grows and forms a nodule, in which the Rhizobium fixes N2 and the plant provides sugars, amino acids, etc.
During growth in the rhizosphere of a host plant, rhizobia sense?
Compounds such as flavonoids and betaines secreted by the host root and respond by inducing nod genes.