LSU ENVS 2126 — Test Questions
Questions with Answers
1. Which domain of life includes organisms that lack a membrane-bound nucleus and
have peptidoglycan cell walls?
A) Eukarya
B) Bacteria
C) Archaea
D) Protista
Answer: B) Bacteria
Rationale: Bacteria are prokaryotic, lack a nucleus, and their cell walls contain
peptidoglycan, distinguishing them from Archaea (different wall chemistry) and Eukarya
(membrane-bound nucleus).
2. What is the primary function of a bacterial flagellum?
A) DNA replication
B) Motility
C) Photosynthesis
D) Nutrient storage
Answer: B) Motility
Rationale: Flagella are whip-like appendages that rotate to propel bacteria through
liquid environments, enabling chemotaxis toward nutrients or away from toxins.
3. Which of the following best describes an obligate anaerobe?
A) An organism that requires oxygen to survive
B) An organism that is poisoned or killed by oxygen
C) An organism that can survive with or without oxygen
D) An organism that only grows at low oxygen levels
Answer: B) An organism that is poisoned or killed by oxygen
Rationale: Obligate anaerobes lack enzymes like catalase and superoxide dismutase to
detoxify reactive oxygen species, so oxygen exposure is lethal to them.
4. Gram-positive bacteria stain purple/violet because:
A) They have a thin peptidoglycan layer that lets stain wash out
, B) They have a thick peptidoglycan layer that retains crystal violet
C) They contain an outer lipopolysaccharide membrane
D) They lack a cell wall entirely
Answer: B) They have a thick peptidoglycan layer that retains crystal violet
Rationale: The thick peptidoglycan layer in gram-positive cell walls traps the crystal
violet-iodine complex during the decolorization step, retaining the purple color.
5. Which structure allows some bacteria to survive extreme heat, desiccation, or
chemical exposure for long periods?
A) Pilus
B) Capsule
C) Endospore
D) Ribosome
Answer: C) Endospore
Rationale: Endospores are dormant, highly resistant structures formed by some bacteria
(e.g., Bacillus, Clostridium) under stress, protecting DNA until conditions improve.
6. Binary fission in bacteria results in:
A) Genetically diverse offspring via meiosis
B) Two genetically identical daughter cells
C) Four haploid spores
D) A single fused diploid cell
Answer: B) Two genetically identical daughter cells
Rationale: Binary fission is asexual reproduction; the parent cell replicates its DNA and
divides into two clonal daughter cells.
7. Which of the following is NOT one of the three domains of life?
A) Bacteria
B) Archaea
C) Eukarya
D) Protozoa
Answer: D) Protozoa
Rationale: Protozoa is an informal classification within Eukarya, not one of the three
domains (Bacteria, Archaea, Eukarya).
,8. Viruses are considered non-living by most biologists because they:
A) Cannot mutate
B) Lack independent metabolism and cannot reproduce without a host cell
C) Are too small to be observed
D) Do not contain genetic material
Answer: B) Lack independent metabolism and cannot reproduce without a host cell
Rationale: Viruses have no ribosomes or metabolic machinery of their own; they must
hijack a host cell's machinery to replicate, so they don't meet the criteria of independent
life.
9. Which term describes microorganisms that thrive in the presence of oxygen but can
also grow without it?
A) Obligate aerobe
B) Facultative anaerobe
C) Obligate anaerobe
D) Microaerophile
Answer: B) Facultative anaerobe
Rationale: Facultative anaerobes can switch between aerobic respiration and
fermentation/anaerobic respiration depending on oxygen availability.
10. What is the main role of decomposer microorganisms in an ecosystem?
A) Fixing atmospheric nitrogen only
B) Breaking down organic matter and recycling nutrients
C) Producing oxygen via photosynthesis
D) Causing disease in plants and animals
Answer: B) Breaking down organic matter and recycling nutrients
Rationale: Decomposers (bacteria and fungi) mineralize dead organic material, releasing
carbon, nitrogen, and other nutrients back into the environment for reuse.
11. Which of the following best defines a pathogen?
A) Any bacterium found in soil
B) A microorganism capable of causing disease
C) A virus that only infects bacteria
D) An organism that lives symbiotically without harm
Answer: B) A microorganism capable of causing disease
, Rationale: Pathogens are microorganisms (bacteria, viruses, fungi, protozoa) that can
cause disease in a host organism.
12. The process by which bacteria take up free DNA from their environment is called:
A) Conjugation
B) Transduction
C) Transformation
D) Binary fission
Answer: C) Transformation
Rationale: Transformation is the uptake and incorporation of naked extracellular DNA
by a competent bacterial cell, a mechanism of horizontal gene transfer.
13. Which type of microscopy is typically used to observe internal cell structures at the
highest resolution?
A) Light microscopy
B) Electron microscopy
C) Naked eye observation
D) Phase-contrast microscopy
Answer: B) Electron microscopy
Rationale: Electron microscopes use electron beams with much shorter wavelengths
than light, achieving far higher resolution needed to see organelles and viruses.
14. Nitrogen-fixing bacteria such as Rhizobium are ecologically important because
they:
A) Convert atmospheric N2 into a usable form (ammonia) for plants
B) Decompose dead plant matter into CO2
C) Convert nitrate into atmospheric nitrogen
D) Produce oxygen during photosynthesis
Answer: A) Convert atmospheric N2 into a usable form (ammonia) for plants
Rationale: Rhizobium species live symbiotically in legume root nodules and fix inert N2
gas into ammonia, making nitrogen bioavailable to plants.
15. Which of these is a characteristic unique to Archaea that distinguishes them from
Bacteria?
A) Presence of ribosomes
Questions with Answers
1. Which domain of life includes organisms that lack a membrane-bound nucleus and
have peptidoglycan cell walls?
A) Eukarya
B) Bacteria
C) Archaea
D) Protista
Answer: B) Bacteria
Rationale: Bacteria are prokaryotic, lack a nucleus, and their cell walls contain
peptidoglycan, distinguishing them from Archaea (different wall chemistry) and Eukarya
(membrane-bound nucleus).
2. What is the primary function of a bacterial flagellum?
A) DNA replication
B) Motility
C) Photosynthesis
D) Nutrient storage
Answer: B) Motility
Rationale: Flagella are whip-like appendages that rotate to propel bacteria through
liquid environments, enabling chemotaxis toward nutrients or away from toxins.
3. Which of the following best describes an obligate anaerobe?
A) An organism that requires oxygen to survive
B) An organism that is poisoned or killed by oxygen
C) An organism that can survive with or without oxygen
D) An organism that only grows at low oxygen levels
Answer: B) An organism that is poisoned or killed by oxygen
Rationale: Obligate anaerobes lack enzymes like catalase and superoxide dismutase to
detoxify reactive oxygen species, so oxygen exposure is lethal to them.
4. Gram-positive bacteria stain purple/violet because:
A) They have a thin peptidoglycan layer that lets stain wash out
, B) They have a thick peptidoglycan layer that retains crystal violet
C) They contain an outer lipopolysaccharide membrane
D) They lack a cell wall entirely
Answer: B) They have a thick peptidoglycan layer that retains crystal violet
Rationale: The thick peptidoglycan layer in gram-positive cell walls traps the crystal
violet-iodine complex during the decolorization step, retaining the purple color.
5. Which structure allows some bacteria to survive extreme heat, desiccation, or
chemical exposure for long periods?
A) Pilus
B) Capsule
C) Endospore
D) Ribosome
Answer: C) Endospore
Rationale: Endospores are dormant, highly resistant structures formed by some bacteria
(e.g., Bacillus, Clostridium) under stress, protecting DNA until conditions improve.
6. Binary fission in bacteria results in:
A) Genetically diverse offspring via meiosis
B) Two genetically identical daughter cells
C) Four haploid spores
D) A single fused diploid cell
Answer: B) Two genetically identical daughter cells
Rationale: Binary fission is asexual reproduction; the parent cell replicates its DNA and
divides into two clonal daughter cells.
7. Which of the following is NOT one of the three domains of life?
A) Bacteria
B) Archaea
C) Eukarya
D) Protozoa
Answer: D) Protozoa
Rationale: Protozoa is an informal classification within Eukarya, not one of the three
domains (Bacteria, Archaea, Eukarya).
,8. Viruses are considered non-living by most biologists because they:
A) Cannot mutate
B) Lack independent metabolism and cannot reproduce without a host cell
C) Are too small to be observed
D) Do not contain genetic material
Answer: B) Lack independent metabolism and cannot reproduce without a host cell
Rationale: Viruses have no ribosomes or metabolic machinery of their own; they must
hijack a host cell's machinery to replicate, so they don't meet the criteria of independent
life.
9. Which term describes microorganisms that thrive in the presence of oxygen but can
also grow without it?
A) Obligate aerobe
B) Facultative anaerobe
C) Obligate anaerobe
D) Microaerophile
Answer: B) Facultative anaerobe
Rationale: Facultative anaerobes can switch between aerobic respiration and
fermentation/anaerobic respiration depending on oxygen availability.
10. What is the main role of decomposer microorganisms in an ecosystem?
A) Fixing atmospheric nitrogen only
B) Breaking down organic matter and recycling nutrients
C) Producing oxygen via photosynthesis
D) Causing disease in plants and animals
Answer: B) Breaking down organic matter and recycling nutrients
Rationale: Decomposers (bacteria and fungi) mineralize dead organic material, releasing
carbon, nitrogen, and other nutrients back into the environment for reuse.
11. Which of the following best defines a pathogen?
A) Any bacterium found in soil
B) A microorganism capable of causing disease
C) A virus that only infects bacteria
D) An organism that lives symbiotically without harm
Answer: B) A microorganism capable of causing disease
, Rationale: Pathogens are microorganisms (bacteria, viruses, fungi, protozoa) that can
cause disease in a host organism.
12. The process by which bacteria take up free DNA from their environment is called:
A) Conjugation
B) Transduction
C) Transformation
D) Binary fission
Answer: C) Transformation
Rationale: Transformation is the uptake and incorporation of naked extracellular DNA
by a competent bacterial cell, a mechanism of horizontal gene transfer.
13. Which type of microscopy is typically used to observe internal cell structures at the
highest resolution?
A) Light microscopy
B) Electron microscopy
C) Naked eye observation
D) Phase-contrast microscopy
Answer: B) Electron microscopy
Rationale: Electron microscopes use electron beams with much shorter wavelengths
than light, achieving far higher resolution needed to see organelles and viruses.
14. Nitrogen-fixing bacteria such as Rhizobium are ecologically important because
they:
A) Convert atmospheric N2 into a usable form (ammonia) for plants
B) Decompose dead plant matter into CO2
C) Convert nitrate into atmospheric nitrogen
D) Produce oxygen during photosynthesis
Answer: A) Convert atmospheric N2 into a usable form (ammonia) for plants
Rationale: Rhizobium species live symbiotically in legume root nodules and fix inert N2
gas into ammonia, making nitrogen bioavailable to plants.
15. Which of these is a characteristic unique to Archaea that distinguishes them from
Bacteria?
A) Presence of ribosomes
