Respiratory Processes Defined by Electron Donor Flashcards
What type of molecule serves as the electron donor for chemoorgano(hetero)trophs?
Organic molecules
What type of molecule serves as the electron donor for chemolitho(auto)trophs?
Inorganic molecules
What is the major difference between aerobic and anaerobic respiration?
Aerobic respiration uses oxygen as the terminal electron acceptor, while anaerobic respiration uses other electron acceptors.
What is the major differences between anaerobic respiration and fermentation?
Anaerobic respiration uses an electron transport chain, while fermentation does not.
Why did aerobic respiration become the dominant form of respiration on Earth?
It is more efficient in producing ATP compared to anaerobic processes.
Why are anoxic habitats still widely spread in nature? (2 reasons)
- They provide niches for specialized organisms. 2. They are formed in environments with limited oxygen availability.
Why are organisms that use more electronegative electron acceptors typically obligate anaerobes?
They cannot survive in the presence of oxygen, which is toxic to them.
What happens to nitrate, sulfate, and carbon dioxide during assimilative reduction?
They are converted into organic compounds.
What happens to nitrate, sulfate, and carbon dioxide during dissimilative reduction?
They are reduced to gases or other inorganic compounds.
What are the major differences between assimilative and dissimilative reductions?
Assimilative reduction incorporates substrates into biomass, while dissimilative reduction does not.
What is a mixotroph?
An organism that can use both organic and inorganic compounds for energy.
The reactions of what trophic group of microbes form the heart of the major nutrient cycles?
Decomposers
What is the overall chemical reaction used by aerobic ‘hydrogen bacteria’ to produce ATP? What enzyme catalyzes this reaction?
2H2 + O2 → 2H2O
Catalyzed by hydrogenase.
What is the source of most of the hydrogen that is oxidized by hydrogen bacteria?
Hydrogen gas produced by anaerobic processes.
Some hydrogen bacteria make two different hydrogenase enzymes. What advantage do these bacteria have over ones that only make a membrane-bound hydrogenase?
They can utilize hydrogen more efficiently under varying environmental conditions.
Most hydrogen bacteria are facultative chemolithotrophs. What does this mean?
They can switch between using inorganic compounds and organic compounds for energy.
What method is used by most hydrogen bacteria to fix carbon when growing autotrophically?
Calvin cycle
Why do oxic environments typically contain very low levels of H2? (2 reasons)
- H2 is rapidly oxidized. 2. Oxygen is a more favorable electron acceptor.
What are the four most common sulfur compounds used as electron donors?
Sulfide, thiosulfate, sulfate, and elemental sulfur.
In most cases, what is the final product of sulfur-compound oxidation?
Sulfate
The first step of sulfide oxidation produces what substance? How is this substance ‘stored’ by bacterial cells?
Sulfite
Stored as intracellular granules.
Why have many sulfur bacteria evolved to be acid-tolerant or acidophilic?
To thrive in acidic environments where they can outcompete other organisms.
What is the Sox system?
A biochemical pathway for the oxidation of sulfur compounds.
Elements of the Sox system have been found in what two trophic groups of prokaryotes? How do these two groups differ in their use of sulfur compound oxidation?
Chemolithotrophs and phototrophs; chemolithotrophs use sulfur compounds for energy, while phototrophs use light.
