Question

22. (a) A person inhales dust and pathogens but does not always fall sick. Explain how the body protects against such infections.

(b) Name and describe any two barriers involved in this protection.

Hint:

Innate immunity is the first defence. It has four barriers: physical, physiological, cellular and cytokine.

Answer 1

Step 1: Understand the question:
Dust and germs enter the nose with every breath, yet we do not fall ill each time.
This is because the body has a defence system called immunity.
Part (a) asks how the body protects itself, and part (b) asks for two named barriers.

Step 2: Part (a): Innate immunity stops the entry and growth of germs:
Innate immunity is the non-specific defence present from birth.
It puts up barriers at the entry points and kills most pathogens before they cause disease.
If a pathogen still gets through, acquired immunity (B and T lymphocytes with memory) deals with it.

Step 3: Part (b): Barrier 1 - physical barrier:
The skin is the main physical barrier of the body.
Mucus coating the epithelium of the respiratory, gastrointestinal and urogenital tracts traps microbes and dust.
Cilia in the nose and windpipe then sweep the trapped particles out.

Step 4: Part (b): Barrier 2 - physiological barrier:
Acid in the stomach, saliva in the mouth and tears from the eyes stop the growth of microbes.
For example, the low pH of the stomach kills most swallowed germs.

Step 5: Other barriers for reference:
Cellular barrier: leukocytes such as neutrophils, monocytes and natural killer cells, and macrophages, engulf microbes by phagocytosis.
Cytokine barrier: virus-infected cells secrete interferons, which protect nearby cells from infection.

Final Answer:
The body protects itself by innate immunity, which works through barriers. Two such barriers are the physical barrier (skin and mucus) and the physiological barrier (stomach acid, saliva, tears).