Question

which of the following is not a physical barrier that helps prevent entry of microbes into the body?
a intact skin
b mucous membranes
c stomach acid
d ciliated cells

Explanation:

To solve this, we analyze each option:

• Option A (Intact skin): It is a physical barrier as it physically blocks microbes from entering the body.
• Option B (Mucous membranes): These are physical barriers (e.g., in the respiratory, digestive tracts) that trap or block microbes.
• Option C (Stomach acid): Stomach acid is a chemical barrier (due to its acidic nature, it kills microbes chemically), not a physical barrier.
• Option D (Ciliated cells): Ciliated cells (e.g., in the respiratory tract) physically move mucus (with trapped microbes) out, acting as a physical barrier.

So, stomach acid is not a physical barrier.

Answer:

C. Stomach acid