Domain Bacteria and Archaea

Which domain includes extremophiles like halophiles and thermophiles?
A. Eukarya
B. Bacteria
C. Archaea
D. Protista

Answer: C (Key: Archaea thrive in extreme environments like salt lakes and hydrothermal vents.)

What structural feature distinguishes gram-negative bacteria from gram-positive bacteria?
A. Thick peptidoglycan layer
B. Outer membrane with lipopolysaccharides
C. Absence of a cell wall
D. Presence of a nucleus

Answer: B (Key: Gram-negative bacteria have an outer membrane; gram-positive bacteria have a thick peptidoglycan layer.)

Which bacterial shape describes Streptococcus species?
A. Bacillus (rod-shaped)
B. Coccus (spherical)
C. Spirillum (spiral)
D. Vibrio (comma-shaped)

Answer: B (Key: Streptococcus are spherical cocci, often forming chains.)

What is the primary role of methanogens in ecosystems?
A. Photosynthesis
B. Methane production in anaerobic conditions
C. Oxygen synthesis
D. Decomposition of cellulose in aerobic environments

Answer: B (Key: Methanogens produce methane as a metabolic byproduct in oxygen-free environments like swamps.)

Which term describes bacteria that can survive with or without oxygen?
A. Obligate aerobes
B. Facultative anaerobes
C. Obligate anaerobes
D. Aerotolerant anaerobes

Answer: B (Key: Facultative anaerobes switch between aerobic respiration and fermentation.)

How do cyanobacteria contribute to ecosystems?
A. By decomposing organic matter
B. By fixing nitrogen and producing oxygen via photosynthesis
C. By causing diseases in animals
D. By fermenting dairy products

Answer: B (Key: Cyanobacteria are photoautotrophs that perform oxygenic photosynthesis.)

Which of the following is a harmful effect of bacteria?
A. Fermentation of yogurt
B. Production of antibiotics
C. Causing tuberculosis (Mycobacterium tuberculosis)
D. Serving as probiotics in digestion

Answer: C (Key: Tuberculosis is a bacterial lung infection.)

What color do gram-negative bacteria appear after Gram staining?
A. Purple
B. Pink
C. Blue
D. Green

Answer: B (Key: Gram-negative bacteria stain pink due to their thin peptidoglycan layer.)

Which archaean group thrives in high-temperature environments like hot springs?
A. Halophiles
B. Thermophiles
C. Methanogens
D. Acidophiles

Answer: B (Key: Thermophiles survive in extreme heat, e.g., Vulcanisaeta distributa.)

What is a key difference between Archaea and Bacteria?
A. Archaea have membrane-bound organelles.
B. Archaea lack cell walls.
C. Archaea have unique lipid membranes and thrive in extremes.
D. Archaea are always pathogenic.

Answer: C (Key: Archaea have distinct membrane lipids and adapt to extreme conditions.)