80. Oxygen in human blood is chiefly carried by binding to which pigment?
[RRB Group D — 21 August 2026, Shift 2]
- (A) Chlorophyll
- (B) Haemoglobin
- (C) Myoglobin
- (D) Plasma
Answer: (B) Haemoglobin
Explanation: Haemoglobin is an iron-containing protein inside red blood cells. Each haemoglobin molecule can reversibly bind four oxygen molecules, enabling oxygen pickup in the lungs and delivery to tissues. Myoglobin mainly stores oxygen in muscle, whereas plasma carries only a small dissolved fraction.
79. Consider:
Assertion (A): Veins have thinner walls than arteries.
Reason (R): Veins transport blood under high pressure.
Choose the correct relation.
[RRB Group D — 21 August 2026, Shift 1]
- (A) A false, R true
- (B) Both true, R explains A
- (C) A true, R false
- (D) Both true, R does not explain A
Answer: (C) A true, R false
Explanation: Veins typically carry blood back to the heart under comparatively low pressure, so their walls contain less smooth muscle and elastic tissue than arteries. The assertion is correct but the reason reverses the actual pressure difference. Many veins also possess valves.
78. Assertion (A): Blood pressure rises temporarily during exercise.
Reason (R): Exercise raises heart rate and blood pumped per minute.
[RRB Group D — 19 August 2026, Shift 3]
- (A) Both true, R not explanation
- (B) A false, R true
- (C) A true, R false
- (D) Both true, R explains A
Answer: (D) Both true, R explains A
Explanation: During exercise, the heart usually beats faster and cardiac output rises to deliver oxygen to active muscles. Systolic arterial pressure generally increases, although diastolic pressure may change little. Thus both statements are true and the reason explains the temporary rise in pressure.
77. Which vessels allow rapid exchange of respiratory gases and nutrients with tissues?
[RRB Group D — 17 August 2026, Shift 3]
- (A) Arteries
- (B) Capillaries
- (C) Veins
- (D) Lymph vessels
Answer: (B) Capillaries
Explanation: Capillaries are microscopic vessels whose thin endothelial walls separate blood from surrounding tissue fluid. Their extensive branching provides a large surface for diffusion of oxygen, carbon dioxide and nutrients. Arteries mainly distribute blood, while veins return it to the heart.
76. What is measured using a sphygmomanometer?
[RRB Group D — 10 August 2026, Shift 3]
- (A) Heart rate
- (B) Blood glucose
- (C) Blood pressure
- (D) Body temperature
Answer: (C) Blood pressure
Explanation: A sphygmomanometer measures arterial blood pressure, usually reported in millimetres of mercury. Its reading has systolic and diastolic values corresponding to ventricular contraction and relaxation. It is distinct from a glucometer, thermometer, and instruments used for monitoring pulse rate.
75. Complete the analogy: Platelets : Clotting :: White blood cells : ______.
[RRB Group D — 4 August 2026, Shift 1]
- (A) Mineral storage
- (B) Fighting inflammation
- (C) Oxygen transport
- (D) Connecting joints
Answer: (B) Fighting inflammation
Explanation: Platelets aggregate at sites of vascular injury to help stop bleeding. White blood cells participate in immune defence and inflammatory responses. Neutrophils attack microorganisms, lymphocytes coordinate adaptive immunity, and monocytes develop into tissue macrophages. Red blood cells chiefly transport oxygen.
74. Which structures prevent backward movement of blood during heart contractions?
[RRB Group D — 4 August 2026, Shift 1]
- (A) Arteries
- (B) Valves
- (C) Muscles
- (D) Septa
Answer: (B) Valves
Explanation: The four cardiac valves maintain one-way blood flow by opening and closing according to pressure differences. The tricuspid and mitral valves guard the atrioventricular openings; pulmonary and aortic semilunar valves guard ventricular outlets. Septa instead separate the heart’s chambers.
73. What is the wave of arterial expansion produced when the heart forces blood into an artery called?
[CGPSC Prelims — 2026]
- (A) Heartbeat
- (B) Pulse
- (C) Flow
- (D) Ticking
Answer: (B) Pulse
Explanation: The pulse is a pressure wave travelling along an artery after ventricular systole ejects blood into the aorta. It can be felt over superficial arteries such as the radial artery. The pulse rate normally reflects the number of heartbeats per minute.
72. Which human blood cells directly defend the body against infectious pathogens?
[DSSSB Court Attendant — 3 June 2026, Shift 1]
- (A) White blood cells
- (B) Red blood cells
- (C) Platelets
- (D) Plasma proteins
Answer: (A) White blood cells
Explanation: Leukocytes, or white blood cells, recognise and combat infectious agents. Neutrophils engulf bacteria, lymphocytes provide targeted immune responses, and monocytes help remove invading organisms. Red cells transport respiratory gases and platelets are primarily involved in haemostasis rather than direct pathogen defence.
71. A blood sample contains 8,000 WBCs per mm³. Approximately how many eosinophils and lymphocytes would it contain, respectively?
[NEET — 3 May 2026]
- (A) 160–240 and 1,600–2,000
- (B) 100–120 and 160–200
- (C) 300–500 and 500–700
- (D) 300–500 and 1,200–1,500
Answer: (A) 160–240 and 1,600–2,000
Explanation: Eosinophils ordinarily account for about two to three percent of circulating leucocytes, giving 160–240 cells from a total of 8,000. Lymphocytes commonly constitute twenty to twenty-five percent, yielding 1,600–2,000 cells per cubic millimetre of blood.