Q.The main barrier that prevents the entry of micro-organisms into our body is (A) Antibodies (B) Macrophages (C) Monocytes (D) Skin
You're viewing a preview — the full solution, concept, methods & PYQ mapping are locked.
Start your 14-day free trial to unlock the full solution →The skin acts as a physical and chemical barrier that blocks the entry of most microorganisms into the body. The correct answer is (D) Skin.
The Concept: First Line of Defence
The human body has multiple layers of defence against pathogens. The very first line is non-specific — it doesn't target a particular germ, but blocks all of them from getting in. This is like the outer wall of a fortress. The skin is the most important part of this first line.
Antibodies, macrophages, and monocytes are all part of the second and third lines of defence — they act after a pathogen has already entered the body. The question asks for the barrier that prevents entry, not the system that fights an infection already inside.
A common mistake is to pick antibodies because they are so famous for fighting disease. But antibodies work inside the blood and tissues — they cannot stop a microbe from touching your skin. They only neutralise pathogens that have already breached the outer defences.
Step-by-Step Reasoning
-
Identify what the question is asking
The phrase "prevents the entry" is key. We need a structure that physically or chemically stops microbes from getting into the body at all — not something that kills them after they are already inside.
-
Evaluate each option against this criterion
-
(A) Antibodies — These are Y-shaped proteins produced by B-lymphocytes. They bind to specific antigens on pathogens. But they are found in blood, lymph, and mucosal secretions — not on the outer surface of the body. A microbe on your skin has not yet encountered an antibody. So antibodies do not prevent entry; they act after entry.
-
(B) Macrophages — These are large phagocytic cells that engulf and digest pathogens. They reside in tissues (like the lungs, liver, spleen) and patrol the body. They are part of the second line of defence — they only see microbes that have already crossed a barrier.
-
(C) Monocytes — These are a type of white blood cell that circulates in the blood. When they enter tissues, they mature into macrophages. Again, they are internal defenders, not external barriers. …
-
Unlock everything free for 14 days
- Full step-by-step solutions
- Concept-first explanations
- Methods, shortcuts & mistakes
- PYQ mapping + timed mock tests
Full access for 14 days. No credit card required.