AP-Micro Microbiology: Microbial Ecology and Pathogenesis 2 — Questions and Answers
Question 1: Which term describes the relationship where one organism benefits and the other is neither helped nor harmed?
- Mutualism
- Commensalism (Correct answer)
- Parasitism
- Amensalism
Correct answer: Commensalism
Commensalism is a symbiotic relationship in which one partner benefits while the other experiences no significant effect.
Question 2: A bacterium that can only cause disease when the host's immune system is compromised is classified as a:
- Primary pathogen
- Opportunistic pathogen (Correct answer)
- Commensal organism
- Saprophyte
Correct answer: Opportunistic pathogen
Opportunistic pathogens exploit immunocompromised states and do not normally cause disease in healthy hosts.
Question 3: The term 'Koch's postulates' refers to criteria used to:
- Classify bacteria by Gram stain
- Establish causation between a microbe and a disease (Correct answer)
- Measure bacterial growth rate
- Determine antibiotic resistance
Correct answer: Establish causation between a microbe and a disease
Koch's postulates provide a logical framework for proving that a specific microorganism is the causative agent of a specific disease.
Question 4: Which of the following best describes a biofilm?
- A single-layer suspension of bacteria in liquid
- A structured community of microbes encased in a self-produced matrix (Correct answer)
- A thin film of nutrients on laboratory media
- A viral protein coat surrounding host cells
Correct answer: A structured community of microbes encased in a self-produced matrix
Biofilms are structured microbial communities embedded in an extracellular polymeric substance (EPS) matrix attached to surfaces.
Question 5: Nitrogen fixation in ecosystems is primarily performed by:
- Fungi and protozoa
- Certain bacteria and archaea (Correct answer)
- Algae and diatoms
- Viruses integrated into plant DNA
Correct answer: Certain bacteria and archaea
Prokaryotes such as Rhizobium, Azotobacter, and certain cyanobacteria contain nitrogenase and can fix atmospheric N₂ into usable ammonia.
Question 6: Exotoxins differ from endotoxins primarily because exotoxins are:
- Part of the outer membrane of Gram-negative bacteria
- Secreted proteins produced by living bacteria (Correct answer)
- Always heat-stable lipopolysaccharides
- Released only upon bacterial death
Correct answer: Secreted proteins produced by living bacteria
Exotoxins are proteinaceous molecules actively secreted by bacteria (both Gram-positive and Gram-negative) and are generally heat-labile.
Question 7: Which ecological concept describes the role a microorganism plays in its environment, including its resource use and interactions?
- Habitat
- Niche (Correct answer)
- Biome
- Ecotone
Correct answer: Niche
An organism's niche encompasses its functional role, resource use, and interactions within an ecosystem.
AP-Micro Microbiology: Microbial Ecology and Pathogenesis 2
Which term describes the relationship where one organism benefits and the other is neither helped nor harmed?