AP® BIOLOGY
SCORING GUIDELINES
Question 6
1.
Bacteria play central biological roles.
(a) Bacteria may act as
 producers
 parasites
 mutualistic symbionts
 decomposers
Select THREE of the ecological roles above. For each one you choose, describe how bacteria carry out
the role and discuss its ecological importance.
(b) Explain the role of bacteria in any two biogeochemical cycles.
* Credit will only be given for the first THREE roles discussed.
6 points max, must include at least one item from each column
Role
How Bacteria Carry out the Role
Producers
 Photosynthetic bacteria
 Cyanobacteria act as
photoautotrophs
 Chemoautotrophs oxidize inorganic
substances
Parasites
 Examples of pathogenic bacteria.
 Cellular parasites
 Internal parasites
 External parasites
Mutualistic Symbionts
 Ruminants and Ungulates
 Nitrogen Fixation
 Nutrient synthesis
 Microbial antagonism
Decomposers
 Chemoheterotrophs
 Digesting organic molecules
Ecological Importance
 Provide energy for an ecosystem.
 Primary producers form first level of
pyramid of energy.


Provide nutrition for other organisms
Maintain population equilibrium


Provide nutrients for organisms
Prevent disease in populations


Recycle nutrients from biomass
Nitrogen, Carbon, Phosphorus
(B) Explain the role of bacteria in any two biogeochemical cycles. (4 points max)
Nitrogen Cycle
 Biological Nitrogen Fixation
 Rhizobia in legumes
 Nitrogen fixing archaea free living
 Decomposers break amino acids into ammonia (ammonification)
 Nitrifying bacteria convert ammonia into nitrites and nitrates
 Denitrification converts nitrates into atmospheric N2
 Denitrifying bacteria use nitrates as final electron acceptor.
Carbon Cycle
 Carbon fixation by Photoautotrophs
 Carbon fixation by Cyanobacteria
 Breakdown and release of carbon through respiration
 Heterotrophic bacteria produce CO2 in repspiration
 Heterotrophic Decomposers produce CO2 in the presence of O2
Phosphorus Cycle
 Bacteria decompose nucleotides into inorganic phosphorus
 Bacteria incorporate ionic phosphates into nucleotides
 Bacteria incorporate ionic phosphates into phospholipids
 Bacteria convert excreted phophate waste into inorganic phosphorus