Microbiology Practice Exam

Test yourself under real exam conditions: 50 timed questions, 60 on the clock, pass mark 70%%. Instant score with a full review of everything you got wrong. Free — no account needed.

📝 50 questions · ⏱ 60 minutes · 🎯 Pass mark 70% · 🆓 Free, no signup

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Exam details

✓50 questions drawn from 200 cards
✓Countdown timer — auto-submits when time runs out
✓Pass mark 70% (real certification threshold)
✓Full review of wrong answers at the end
✓No signup required — save your score with a free account

Sample Questions

5 shown

What is the basic structural difference between Gram-positive and Gram-negative cell walls?

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Gram-positive bacteria have a thick peptidoglycan layer and no outer membrane; Gram-negative bacteria have a thin peptidoglycan layer plus an outer membrane containing lipopolysaccharide (LPS).

What color do Gram-positive bacteria appear after Gram staining?

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Purple/violet (retain crystal violet-iodine complex).

What color do Gram-negative bacteria appear after Gram staining?

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Pink/red (crystal violet is washed out by decolorizer; counterstained with safranin).

What are the four main steps of the Gram stain procedure, in order?

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1) Crystal violet (primary stain) 2) Gram's iodine (mordant) 3) Alcohol/acetone decolorizer 4) Safranin (counterstain).

What molecule in the outer membrane of Gram-negative bacteria acts as an endotoxin?

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Lipopolysaccharide (LPS), specifically its lipid A component.

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