UPSC Prelims 2002 Q26: Science & Technology – Biology
With reference to the blood in a normal person,
which one of the following statements is correct?
- (a) Compared to arteries, veins are less numerous and hold less of the body’s blood at any given time
- (b) Blood cells constitute about 70 % of the total volume of the blood
- (c) White Blood Cells (WBC) are made by lymph nodes only
- (d) The blood has more platelets than WBC
Answer: (d) The blood has more platelets than WBC
Explanation
Blood in a normal person: which statement is correct
| Statement | Verdict |
|---|---|
| Veins are less numerous and hold less blood than arteries | False — veins hold about 65 per cent of the blood at any time (the capacitance vessels) |
| Blood cells are about 70% of the volume | False — cells are about 45%, plasma about 55% |
| WBC are made by lymph nodes only | False — WBC are made mainly in the bone marrow; lymph nodes make lymphocytes |
| The blood has more platelets than WBC | True — about 1.5-4 lakh platelets against 4,000-11,000 WBC per mm³ |
A normal person has roughly 150,000-400,000 platelets per cubic millimetre of blood, but only 4,000-11,000 white blood cells. So the blood has more platelets than WBC, and statement (d) is the correct one.
Answer: (d) The blood has more platelets than WBC.
Why each option is right or wrong
- (a) Incorrect. Veins hold most of the blood, not less than arteries.
- (b) Incorrect. Blood cells make up about 45 per cent of the volume, not 70.
- (c) Incorrect. WBC are made in the bone marrow, not by lymph nodes only.
- (d) CORRECT. Platelets (lakhs per mm³) outnumber WBC (thousands per mm³).
Key point
Normal counts per mm³: RBC 4.5-5.5 million, platelets 1.5-4 lakh, WBC 4,000-11,000.
Remember
Platelets outnumber WBC in the blood of a normal person.
Common mistakes
- Thinking the arteries hold most blood because they carry it at high pressure.
- Quoting 70% for blood cells instead of about 45%.
- Believing lymph nodes are the only site of WBC production.
Exam tip
Rank by count: RBC, then platelets, then WBC.
Sources
- NCERT Class XI Biology — Body Fluids and Circulation
- John E. Hall — Guyton and Hall Textbook of Medical Physiology (Red Blood Cells, Anemia, and Polycythemia)