Microorganisms as pathogens — A/L Biology

How do I practise Microorganisms as pathogens?

1 question with a worked solution

1. Which structural and biological property correctly distinguishes bacterial endotoxins from bacterial exotoxins?
   1. A) Endotoxins are heat-stable lipopolysaccharide complexes integrated into the outer membrane of Gram-negative bacteria
   2. B) Endotoxins are readily neutralized by formalin to produce effective toxoid vaccines
   3. C) Endotoxins exhibit extreme tissue-specific pharmacological toxicity at sub-microgram dosages
   4. D) Endotoxins are enzymatic proteins actively secreted into extracellular fluid by viable Gram-positive bacteria
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   Correct answer: A) Endotoxins are heat-stable lipopolysaccharide complexes integrated into the outer membrane of Gram-negative bacteria

   Endotoxins are lipopolysaccharides (LPS, specifically Lipid A) located within the outer membrane of Gram-negative bacteria, released only upon cell lysis or death. They are heat-stable, weakly immunogenic (cannot form toxoids), and cause systemic fever/septic shock via interleukin release. Exotoxins are heat-labile soluble proteins secreted by living bacteria.

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   Step 1: Compare bacterial toxins: - Chemical nature: Exotoxins = Proteins; Endotoxins = Lipopolysaccharide (Lipid A). - Source: Exotoxins = Gram+ and Gram- (secreted); Endotoxins = Gram- outer membrane. - Heat stability: Exotoxin = Heat labile (except staph enterotoxin); Endotoxin = Heat stable. - Toxoids: Exotoxins form toxoids; Endotoxins do not. Answer: Endotoxins are heat-stable lipopolysaccharide complexes integrated into the outer membrane of Gram-negative bacteria.
   Modelled on: the A/L Biology examination pattern

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Where does Microorganisms as pathogens fit in the syllabus?

Year 2 · Term 3