UPSC CSE Prelims
Human Body Systems Previous Year Questions (PYQs)
Practice solved questions for Human Body Systems with detailed step-by-step solutions, key insights, and trend analysis for UPSC CSE PRELIMS.
Solved Previous Year Questions
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Which one of the following is synthesised in human body that dilates blood vessels and increases blood flow ?
Detailed Explanation:
Correct Answer: ✅ Option 1 (Nitric Oxide)
Nitric Oxide (NO) is a signaling molecule naturally produced in the human body from the amino acid L-arginine by the enzyme nitric oxide synthase (NOS). It relaxes the smooth muscles of blood vessels, causing vasodilation (widening of blood vessels), which increases blood flow and helps regulate blood pressure.
✅ Nitric Oxide – Correct: Causes vasodilation and improves blood circulation.
❌ Nitrous Oxide (N₂O) – Incorrect: Commonly known as "laughing gas"; used as an anesthetic and analgesic.
❌ Nitrogen Dioxide (NO₂) – Incorrect: A harmful air pollutant that can damage the respiratory system.
❌ Nitrogen Pentoxide (N₂O₅) – Incorrect: A reactive chemical compound with no role in human vasodilation.
Short Notes: Nitric Oxide (NO)
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Discovered as an important biological messenger; awarded the 1998 Nobel Prize in Physiology or Medicine.
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Produced from L-arginine by nitric oxide synthase (NOS).
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Causes vasodilation, increasing blood flow and lowering blood pressure.
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Plays a key role in cardiovascular health.
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Involved in neurotransmission and immune responses.
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Drugs like Nitroglycerin act by releasing nitric oxide.
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Deficiency of NO may contribute to hypertension and vascular diseases.
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Acts as a short-lived gaseous signaling molecule.
Which one of the following statements best describes the role of B cells and T cells in the human body?
Detailed Explanation:
Answer: Option 4 — They protect the body from the diseases caused by pathogens.
B cells and T cells are both lymphocytes and key components of the adaptive immune system that specifically defend the body against pathogens like viruses, bacteria, fungi, and parasites. B cells produce antibodies that recognize and neutralize specific antigens on pathogens, while T cells either directly kill infected cells (cytotoxic T cells) or help coordinate the immune response (helper T cells).
❌ Option 1 – Incorrect: While immune cells can respond to allergens, the primary role of B and T cells is pathogen defense, not allergen protection.
❌ Option 2 – Incorrect: Pain and inflammation alleviation is not the primary function of B and T cells; they are involved in immune response.
❌ Option 3 – Incorrect: B and T cells are immunoactive, not immunosuppressants; they enhance rather than suppress immune function.
✅ Option 4 – Correct: This accurately describes the primary role of B and T cells in adaptive immunity against pathogenic diseases.
📝 Short Notes: B Cells and T Cells
| Feature | B Cells (B Lymphocytes) | T Cells (T Lymphocytes) |
|---|---|---|
| Maturation Site | Bone marrow | Thymus gland |
| Primary Function | Produce antibodies (humoral immunity) | Cell-mediated immunity |
| Types | Plasma cells, Memory B cells | Helper T cells (CD4+), Cytotoxic T cells (CD8+), Regulatory T cells, Memory T cells |
| Mechanism | Recognize antigens and secrete specific antibodies | Directly kill infected cells or regulate immune response |
| Response Type | Humoral/antibody-mediated immunity | Cell-mediated immunity |
| Memory | Memory B cells provide long-term immunity | Memory T cells enable faster response upon re-exposure |
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