Questions on Bacteria Classification
Multiple-Choice Questions: Bacteria Classification: Morphology, Gram Staining, Shape, Metabolism, and Taxonomy
Morphology & Shape
1. Which of the following is a spherical shaped bacterium?
A) Bacillus
B) Spirillum
C) Vibrio
D) Coccus
E) Filamentous
2. The rod-shaped bacteria are classified as:
A) Cocci
B) Spirilla
C) Bacilli
D) Vibrios
E) Spirochetes
3. Bacteria that are comma-shaped are called:
A) Spirilla
B) Vibrios
C) Bacilli
D) Cocci
E) Actinomycetes
4. Spiral-shaped bacteria with rigid structure are called:
A) Spirochetes
B) Cocci
C) Vibrios
D) Spirilla
E) Filamentous
5. Which of the following describes Streptococcus correctly?
A) Rod-shaped in chains
B) Spherical in clusters
C) Spiral in chains
D) Spherical in chains
E) Rod-shaped in clusters
Gram Staining & Cell Wall
6. Gram-positive bacteria have:
A) Thin peptidoglycan layer and outer membrane
B) No peptidoglycan
C) Thick peptidoglycan layer and no outer membrane
D) Only a cell membrane
E) Lipopolysaccharide-rich outer shell
7. Gram-negative bacteria are characterized by:
A) Thick cell wall
B) No peptidoglycan
C) Absence of lipids
D) Outer membrane and thin peptidoglycan
E) Green pigmentation
8. Which dye is retained by Gram-positive bacteria in staining?
A) Methylene blue
B) Safranin
C) Crystal violet
D) Malachite green
E) Carbol fuchsin
9. After Gram staining, Gram-negative bacteria appear:
A) Purple
B) Blue
C) Yellow
D) Red or pink
E) Colorless
10. The Gram stain technique is used to:
A) Identify bacterial metabolism
B) Determine genetic structure
C) Distinguish between types of cell walls
D) Count bacterial colonies
E) Measure bacterial size
Metabolic Classification
11. Obligate aerobes require:
A) No oxygen at all
B) Oxygen to grow
C) Sunlight for photosynthesis
D) Nitrogen gas only
E) Glucose exclusively
12. Obligate anaerobes:
A) Require oxygen
B) Prefer oxygen but can survive without it
C) Die in the presence of oxygen
D) Live only in sunlight
E) Require carbon dioxide
13. Facultative anaerobes are bacteria that:
A) Die in oxygen
B) Only ferment sugars
C) Can grow with or without oxygen
D) Need UV light
E) Live in acidic conditions only
14. Photoautotrophic bacteria obtain energy from:
A) Organic chemicals
B) Inorganic oxidation
C) Light and CO₂
D) Oxygen and ATP
E) Only from hosts
15. Chemoheterotrophs get both carbon and energy from:
A) Sunlight
B) Carbon dioxide
C) Organic compounds
D) Inorganic salts
E) Water and light
Taxonomy & Other Classifications
16. The two domains where bacteria are classified are:
A) Protista and Plantae
B) Archaea and Bacteria
C) Bacteria and Fungi
D) Monera and Eukarya
E) Eukarya and Archaea
17. Cyanobacteria are classified as:
A) Gram-negative, oxygenic photosynthetic bacteria
B) Gram-positive anaerobes
C) Eukaryotic algae
D) Parasites
E) Viruses
18. Archaea differ from true bacteria (Eubacteria) by:
A) Lacking DNA
B) Having different cell wall components
C) Having mitochondria
D) Being multicellular
E) Possessing chloroplasts
19. Actinobacteria are known for:
A) Nitrogen fixation in roots
B) Being strict pathogens
C) Producing antibiotics
D) Causing the flu
E) Living in extreme cold
20. Enterobacteriaceae is a family that includes:
A) Staphylococcus
B) Bacillus
C) E. coli
D) Mycobacterium
E) Treponema
Answer Key with Explanations
1. D – Cocci are spherical-shaped bacteria.
2. C – Bacilli are rod-shaped.
3. B – Vibrios are comma-shaped.
4. D – Spirilla are rigid spiral-shaped bacteria (spirochetes are flexible).
5. D – Streptococcus refers to spherical cells arranged in chains.
6. C – Gram-positive bacteria have a thick peptidoglycan wall and lack an outer membrane.
7. D – Gram-negative bacteria have a thin peptidoglycan wall and an outer lipid membrane.
8. C – Crystal violet stains Gram-positive bacteria purple.
9. D – Gram-negative bacteria appear pink/red due to the safranin counterstain.
10. C – Gram staining distinguishes types of bacterial cell walls.
11. B – Obligate aerobes require oxygen for survival.
12. C – Obligate anaerobes die in the presence of oxygen.
13. C – Facultative anaerobes can survive with or without oxygen.
14. C – Photoautotrophs use light for energy and CO₂ as a carbon source.
15. C – Chemoheterotrophs get both energy and carbon from organic molecules.
16. B – The two domains are Bacteria and Archaea.
17. A – Cyanobacteria are photosynthetic and Gram-negative.
18. B – Archaea have unique cell wall compositions (no peptidoglycan).
19. C – Actinobacteria like Streptomyces produce antibiotics.
20. C – E. coli is a member of Enterobacteriaceae.
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