Thermal resistance of bacteria — Identify the statement that is NOT true (i.e., false) about how bacterial cell traits affect heat resistance.
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ACocci are usually more resistant than rods
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BThe higher the optimal and maximal growth temperatures, the higher the heat resistance tends to be
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CBacteria that clump considerably or form capsules are more difficult to kill
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DCells low in lipid content are harder to kill than other cells
Answer
Correct Answer: Cells low in lipid content are harder to kill than other cells
Explanation
Introduction / Context:Heat resistance of bacteria varies with morphology, physiology, and cell envelope composition. Recognizing which features increase resistance guides process selection in food preservation, sterilization, and healthcare decontamination.
Given Data / Assumptions:
- We compare shape (cocci vs rods), temperature adaptation, clumping/capsules, and lipid content effects.
- We are looking for the one statement that is NOT true.
Concept / Approach:Gram-positive cocci often exhibit higher resistance than many Gram-negative rods. Thermophiles and organisms adapted to high temperatures usually have more thermostable proteins/membranes, correlating with higher resistance. Clumping or capsules impede heat transfer and protect inner cells. In contrast, high lipid content (for example, in mycobacteria) tends to increase resistance to many agents; therefore, saying “cells low in lipid content are harder to kill” is contrary to general trends and is the false statement.
Step-by-Step Solution:
Evaluate cocci vs rods: cocci commonly more heat-resistant → true.Evaluate growth temperature adaptation: thermophiles more resistant → true.Evaluate clumping/capsules: protective effects → true.Evaluate lipid content claim: low-lipid cells harder to kill → false.Verification / Alternative check:Food microbiology texts cite increased resistance in organisms with waxy, lipid-rich envelopes (e.g., mycobacteria) and in thermophiles; process lethality tables reflect these differences.
Why Other Options Are Wrong:
- Cocci more resistant: consistent with many comparative studies.
- Higher optimal growth temperature → higher resistance: aligns with thermophile biology.
- Clumping/capsules: physical shielding from heat and chemicals.
Common Pitfalls:Overgeneralizing across all taxa; exceptions exist, but the false statement here is the one about low lipid content increasing resistance.
Final Answer:Cells low in lipid content are harder to kill than other cells