Question

Read the following statements (A - D) and select the true (T) and false (F) ones regarding physiological barriers.

A.Lysozyme present in saliva and tears kills viruses by destroying their cell walls.
B.Acid in the stomach destroys bacteria.
C.A rise in body temperature is a natural defence mechanism to destroy pathogens.
D.The sweat and oil secreted make the skin surface alkaline.

• A. A - F, B - T, C - F and D - F
• B. A - F, B - T, C - T and D - T
• C. A - T, B - T, C - T and D - F
• D. A - F, B - T, C - T and D - F

Answer 1

The correct option is D A - F, B - T, C - T and D - F

innate immunity is the immunity present in an individual from birth. Physiological barriers are part of innate immunity. Most bacteria prefer a particular pH (nearly neutral pH) and temperature (32°C - 37°C) for their optimum growth and metabolic activities. Physiological barriers resist infections by increasing the body temperature or by the respective pH values of the body fluids (acidic or alkaline). A rise in temperature (fever) due to infection is a natural defence mechanism to resist multiplication of pathogens.


Lysozyme is an enzyme present in the saliva and tears. It kills many bacteria not viruses by lysing the peptidoglycan in their cell walls. As viruses do not have cell walls and they present inside the host cells lysozyme cannot kill viruses.

Parietal cells of the stomach produce HCl. It has a pH of 2-3. This strong acid kills bacteria. The oil and sweat secreted contains fatty acids and lactic acids which make the skin surface acidic (pH 5.4 - 5.9). This prevents the establishment of microbial colonies on the skin and hence kills them. Hence B and C are true statements and A and D are false statements.