Circulatory System

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.

70. Which altered sixth codon of the beta-globin gene produces the haemoglobin change associated with sickle-cell anaemia?

[NEET — 3 May 2026]

• (A) CAG
• (B) GUG
• (C) AUG
• (D) GAG

Answer: (B) GUG

Explanation: Sickle-cell disease results from a point mutation in the beta-globin coding sequence. The sixth mRNA codon changes from GAG, encoding glutamic acid, to GUG, encoding valine. The resulting haemoglobin S can polymerise under low oxygen conditions, distorting red cells.

69. Why do veins possess valves whereas most arteries do not?

[RRB Technician Grade III — 10 March 2026, Shift 3]

• (A) Veins carry low-pressure blood and need backflow prevention
• (B) Arteries are deep and muscle-supported
• (C) Arteries always carry oxygen-rich blood
• (D) Veins carry higher-pressure blood

Answer: (A) Veins carry low-pressure blood and need backflow prevention

Explanation: Venous blood generally returns towards the heart at lower pressure than arterial blood. Valves within many veins prevent reversal of flow, especially in the limbs where blood moves against gravity. Arteries withstand strong pulses using thick, elastic muscular walls.

68. What are the smallest vessels with walls only one cell thick, formed by branching arteries?

[RRB ALP CBT-I — 17 February 2026, Shift 1]

• (A) Arteries
• (B) Capillaries
• (C) Veins
• (D) Arterioles

Answer: (B) Capillaries

Explanation: Arterioles branch into capillary networks within organs. Capillaries have walls mainly one endothelial cell thick, allowing short diffusion distances for gases, nutrients and waste. Their blood ultimately drains through venules into veins. Arteries and arterioles possess thicker muscular walls.

67. What is the fluid matrix of blood in which its cellular elements remain suspended?

[RRB Group D — 6 February 2026, Shift 1]

• (A) Platelets
• (B) Red blood cells
• (C) Plasma
• (D) White blood cells

Answer: (C) Plasma

Explanation: Plasma is the straw-coloured liquid matrix of blood and makes up approximately fifty-five percent of blood volume. It consists predominantly of water with proteins, salts, nutrients, hormones and wastes. Red cells, white cells and platelets are suspended within it.

66. Which of these is not itself a tissue?

[RRB Group D — 4 February 2026, Shift 3]

• (A) Nerves
• (B) Red blood cells
• (C) Muscles
• (D) Blood

Answer: (B) Red blood cells

Explanation: Blood is classified as specialised connective tissue, and muscles and nerves consist of organised tissue structures. A red blood cell is an individual cellular component of the blood tissue, not a distinct tissue in itself. Mature human RBCs also lack nuclei.

65. In human blood, oxygen is mainly transported by which component?

[RRB Group D — 3 February 2026, Shift 1]

• (A) Blood platelets
• (B) Lymph
• (C) Red blood corpuscles
• (D) White blood corpuscles

Answer: (C) Red blood corpuscles

Explanation: Red blood corpuscles contain haemoglobin, which binds oxygen reversibly in lung capillaries and releases it in tissue capillaries. Their biconcave shape increases exchange efficiency. White cells defend against infection and platelets support clotting; neither is the principal oxygen carrier.

64. The blood pressure observed when the heart relaxes is called ______.

[RRB NTPC Graduate Level CBT-II — 13 October 2025, Shift 2]

• (A) Diastolic pressure
• (B) Pulse pressure
• (C) Venous pressure
• (D) Systolic pressure

Answer: (A) Diastolic pressure

Explanation: Diastolic pressure is the minimum arterial pressure during ventricular relaxation between heartbeats. In a commonly quoted reading of 120/80 mmHg, 80 represents the diastolic component. Systolic pressure is measured during ventricular contraction, while pulse pressure is their numerical difference.

63. Which statements about blood are correct?
(1) It contains plasma and different cell types.
(2) Haemoglobin gives blood its red appearance.

[UPPSC PCS Prelims — 2025, GS Paper I]

• (A) Only statement 1
• (B) Both statements 1 and 2
• (C) Neither statement
• (D) Only statement 2

Answer: (B) Both statements 1 and 2

Explanation: Blood comprises liquid plasma and formed elements: erythrocytes, leucocytes and platelets. Its familiar red colour is mainly due to haemoglobin, an iron-bearing oxygen transport protein inside erythrocytes. Both statements correctly describe the composition and appearance of circulating blood.

62. Which vessels carry oxygenated blood away from the heart to most parts of the body?

[RRB NTPC Undergraduate CBT-I — 18 August 2025, Shift 2]

• (A) Veins
• (B) Venules
• (C) Capillaries
• (D) Arteries

Answer: (D) Arteries

Explanation: Systemic arteries convey oxygen-rich blood from the left ventricle through the aorta towards tissues. The pulmonary artery is a notable exception: it carries oxygen-poor blood from the right ventricle to the lungs. Veins usually direct blood back towards the heart.

61. What is the scientific name for white blood cells?

[SSC Stenographer — 6 August 2025, Shift 1]

• (A) Erythrocytes
• (B) Leucocytes
• (C) Thrombocytes
• (D) Platelets

Answer: (B) Leucocytes

Explanation: Leucocytes, also spelt leukocytes, are the nucleated defensive cells of blood. They include neutrophils, eosinophils, basophils, lymphocytes and monocytes. Erythrocytes are red blood cells, while thrombocytes or platelets chiefly participate in arresting bleeding after vessel damage.

60. Which blood cells protect the body against infections?

[SSC Selection Post, Matriculation Level — 2 August 2025, Shift 1]

• (A) Red blood cells
• (B) White blood cells
• (C) Platelets
• (D) Plasma

Answer: (B) White blood cells

Explanation: White blood cells form a crucial cellular component of innate and adaptive immunity. Some engulf pathogens, while lymphocytes mediate targeted defence and antibody responses. Red blood cells transport oxygen; platelets support clot formation, and plasma is the liquid transport medium.

59. Blood pressure is measured with which apparatus?

[BSSC Group D — 11 May 2025]

• (A) Thermometer
• (B) Barometer
• (C) Crescograph
• (D) Sphygmomanometer

Answer: (D) Sphygmomanometer

Explanation: A sphygmomanometer records arterial pressure through an inflatable cuff and pressure measuring system. The device yields systolic and diastolic values, commonly expressed in mmHg. A barometer measures atmospheric pressure, a thermometer measures temperature, and a crescograph measures plant growth.

58. Which instrument is used for manually measuring a person’s blood pressure?

[UPSC CDS-I, General Knowledge — 13 April 2025]

• (A) Sphygmomanometer
• (B) Centrifuge
• (C) Electrophoresis apparatus
• (D) Thermal cycler

Answer: (A) Sphygmomanometer

Explanation: Manual pressure assessment uses a sphygmomanometer cuff with a gauge, often alongside a stethoscope to detect arterial Korotkoff sounds. The pressure at sound appearance estimates systolic pressure; disappearance usually estimates diastolic pressure. The other instruments serve laboratory separation or amplification functions.

57. Which activity is NOT a function of circulating blood?

[RRB Technician Grade III — 30 December 2024, Shift 1]

• (A) Making starch
• (B) Transporting gases
• (C) Carrying hormones
• (D) Carrying wastes

Answer: (A) Making starch

Explanation: Blood transports oxygen, carbon dioxide, hormones, nutrients and metabolic waste throughout the body. Starch synthesis occurs chiefly in photosynthetic plant tissues and is not a function of human blood. Circulating blood additionally assists temperature regulation, immunity and internal fluid balance.

56. Which of the following is classified as a connective tissue?

[RRB Technician Grade III — 27 December 2024, Shift 3]

• (A) Cuboidal epithelium
• (B) Muscle
• (C) Blood
• (D) Columnar epithelium

Answer: (C) Blood

Explanation: Blood is specialised fluid connective tissue because living cellular elements are suspended within an extracellular matrix called plasma. Its transport role links different tissues throughout the body. Epithelial tissues mainly line surfaces, and muscle tissue specialises in contraction and movement.

55. Which human organ pumps blood around the body?

[RRB Technician Grade III — 27 December 2024, Shift 3]

• (A) Pancreas
• (B) Heart
• (C) Stomach
• (D) Liver

Answer: (B) Heart

Explanation: The muscular heart maintains blood circulation by alternating relaxation and contraction. Its right half pumps blood to the lungs, while the left half pumps oxygenated blood into systemic arteries. Four chambers and coordinated valves maintain efficient, largely one-way flow throughout the body.

54. Which substance is NOT normally present as a dissolved constituent of blood plasma?

[RRB Technician Grade III — 27 December 2024, Shift 3]

• (A) Salts
• (B) Proteins
• (C) Undigested food
• (D) Hormones

Answer: (C) Undigested food

Explanation: Plasma contains water, proteins, electrolytes, nutrients, hormones and metabolic wastes. Food is first digested into absorbable molecules before entering the circulation; undigested food remains within the digestive tract. Albumin, globulins and fibrinogen are major classes of plasma proteins.

53. Which statements about vessels are correct?
(i) Arteries carry blood away from the heart;
(ii) arteries have thin elastic walls;
(iii) venous valves prevent backflow.

[RRB Technician Grade III — 23 December 2024, Shift 2]

• (A) Only (i) and (iii)
• (B) Only (i) and (ii)
• (C) All three
• (D) Only (i)

Answer: (A) Only (i) and (iii)

Explanation: Arteries conduct blood outward from the heart and require thick muscular elastic walls to handle pulsatile pressure. Therefore the assertion that their walls are thin is false. Many veins contain valves which prevent reverse flow during low-pressure venous return.

52. Which pigment is present in human red blood corpuscles?

[RRB Technician Grade III — 23 December 2024, Shift 3]

• (A) Melanin
• (B) Xanthophyll
• (C) Haemoglobin
• (D) Chlorophyll

Answer: (C) Haemoglobin

Explanation: Haemoglobin is a protein containing iron-bearing haem groups, which gives red blood cells their characteristic colour. It reversibly binds oxygen in the lungs and releases it to body tissues. Melanin colours skin and hair; chlorophyll and xanthophyll are plant pigments.

51. Which blood component carries dissolved nutrients, carbon dioxide and nitrogenous wastes?

[RRB Technician Grade III — 23 December 2024, Shift 2]

• (A) Plasma
• (B) Blood platelets
• (C) Lymph
• (D) Red blood corpuscles

Answer: (A) Plasma

Explanation: Plasma carries dissolved materials, including glucose, mineral ions, hormones and urea. Some carbon dioxide is carried as dissolved gas, but most travels in the blood as bicarbonate. The fluid plasma matrix distributes these substances among organs responsible for nutrition and excretion.

50. Complete the analogy: Blood : connective tissue :: Bone : ______.

[RRB Technician Grade III — 20 December 2024, Shift 3]

• (A) Muscular tissue
• (B) Epithelial tissue
• (C) Nervous tissue
• (D) Connective tissue

Answer: (D) Connective tissue

Explanation: Bone and blood both belong to the connective tissue family, although their matrices differ greatly. Bone has a mineralised solid matrix for support and protection, whereas blood has a fluid plasma matrix for transport. Muscle and nervous tissues have separate primary functions.

49. Deficiency of which vitamin may lead to prolonged bleeding from wounds?

[SSC MTS — 21 October 2024, Shift 1]

• (A) Vitamin E
• (B) Vitamin A
• (C) Vitamin B12
• (D) Vitamin K

Answer: (D) Vitamin K

Explanation: Vitamin K is required for activation of several coagulation proteins, including prothrombin and factors VII, IX and X. Deficiency impairs normal clot formation, sometimes producing abnormal bleeding. The vitamin is therefore important to the haemostatic function of the circulatory system.

48. Which agglutinogens occur on the red cells of a person with blood group O?

[RPSC RAS Prelims — 2023]

• (A) Both A and B
• (B) Only B
• (C) Neither A nor B
• (D) Only A

Answer: (C) Neither A nor B

Explanation: In the ABO classification, type O red cells possess neither A nor B antigen on their surfaces. Their plasma normally contains anti-A and anti-B antibodies. Rh status is a separate feature; therefore O positive and O negative are not interchangeable for every recipient.

47. Which of these medical-specialist pairings is incorrect?

[WBCS (Executive) Prelims — 2023]

• (A) Kidney diseases — urologist
• (B) Blood diseases — haematologist
• (C) Stomach diseases — gastroenterologist
• (D) Cancer — oncologist

Answer: (A) Kidney diseases — urologist

Explanation: A haematologist specialises in conditions involving blood and its forming tissues, including anaemia and leukaemia. Although urologists treat the urinary tract surgically, a nephrologist is the more specific physician for many medical kidney diseases; therefore that pairing is the incorrect one.

46. A sphygmomanometer is primarily used to measure what?

[SSC CGL — 14 July 2023, Memory-Based Paper]

• (A) Blood glucose
• (B) Blood pressure
• (C) Cholesterol
• (D) Uric acid

Answer: (B) Blood pressure

Explanation: A sphygmomanometer measures pressure exerted by flowing blood on arterial walls. Traditional readings are expressed as systolic over diastolic pressure, in millimetres of mercury. Blood glucose requires a glucometer, while cholesterol and uric acid are generally determined through laboratory blood analysis.

45. Which vessels carry blood from the heart to the different organs of the body?

[SSC MTS — 15 June 2023, Shift 1]

• (A) Veins
• (B) Tracheae
• (C) Arteries
• (D) Plasma

Answer: (C) Arteries

Explanation: Arteries carry blood away from the pumping heart. Their branches, the arterioles, feed capillary networks where exchange with tissues occurs. The pulmonary artery carries oxygen-poor blood, showing that direction of flow, not oxygen content, defines an artery.

44. Which vitamin helps blood clot normally in humans?

[MPPSC State Services Prelims 2022 — held 21 May 2023]

• (A) Vitamin A
• (B) Vitamin B
• (C) Vitamin K
• (D) Vitamin D

Answer: (C) Vitamin K

Explanation: Vitamin K supports activation of important coagulation factors through gamma-carboxylation in the liver. Without adequate vitamin K, the clotting cascade functions poorly and bleeding may persist. It also participates in the metabolism of proteins involved in maintaining healthy bone tissue.

43. In which component of human blood is the respiratory pigment haemoglobin present?

[RRB Group D — 11 October 2022, Shift 2]

• (A) White blood corpuscles
• (B) Red blood corpuscles
• (C) Blood platelets
• (D) Blood plasma

Answer: (B) Red blood corpuscles

Explanation: Haemoglobin is concentrated inside erythrocytes, or red blood corpuscles. Each molecule contains four haem groups capable of binding oxygen reversibly. This arrangement enables blood to transport much more oxygen than could dissolve in plasma alone, supporting aerobic respiration in tissues.

42. The pulmonary vein of the human heart opens into which chamber?

[RRB Group D — 6 October 2022, Shift 2]

• (A) Right atrium
• (B) Left ventricle
• (C) Left atrium
• (D) Right ventricle

Answer: (C) Left atrium

Explanation: Pulmonary veins return oxygenated blood from lung capillaries to the left atrium, also called the left auricle. Blood then flows through the mitral valve into the left ventricle. From there it enters the aorta and supplies the systemic circulation.

41. Which blood constituent provides immune protection against germs?

[RRB Group D — 6 October 2022, Shift 2]

• (A) White blood cells
• (B) Platelets
• (C) Plasma
• (D) Red blood cells

Answer: (A) White blood cells

Explanation: White blood cells collectively protect the body from invading microorganisms and other foreign substances. Phagocytic cells engulf many pathogens, while B and T lymphocytes support specific immune responses. In contrast, erythrocytes convey oxygen and platelets help plug damaged blood vessels.

40. Match: I. Heart; II. Arteries; III. Veins

with A. Pumping organ; B. Carry deoxygenated blood; C. Carry oxygenated blood (usual systemic pattern).

[RRB Group D — 22 September 2022, Shift 1]

• (A) I–C, II–B, III–A
• (B) I–A, II–B, III–C
• (C) I–C, II–A, III–B
• (D) I–A, II–C, III–B

Answer: (D) I–A, II–C, III–B

Explanation: The heart functions as a muscular pump. In systemic circulation, arteries generally deliver oxygen-rich blood to tissues and veins return oxygen-poor blood to the heart. The pulmonary artery and pulmonary veins are major exceptions to this oxygenation pattern, but not to flow direction.

39. What carries most digested and absorbed fats away from the intestine?

[RRB Group D — 14 September 2022, Shift 3]

• (A) Plasma
• (B) Lymph
• (C) Platelets
• (D) Veins

Answer: (B) Lymph

Explanation: Intestinal lacteals, which are specialised lymphatic capillaries, absorb many dietary fats packaged as chylomicrons. The fat-rich lymph later enters the bloodstream through large lymphatic ducts. This route differs from many water-soluble nutrients, which enter the hepatic portal blood.

38. Which fluid transports dissolved food, carbon dioxide and nitrogenous wastes in blood?

[RRB Group D — 13 September 2022, Shift 1]

• (A) Plasma
• (B) White blood cells
• (C) Red blood cells
• (D) Platelets

Answer: (A) Plasma

Explanation: Plasma forms the liquid phase of blood, carrying soluble nutrients, electrolytes and waste materials. Urea travels through plasma towards the kidneys for removal. Most carbon dioxide travels as bicarbonate, with smaller amounts dissolved or bound to blood proteins, including haemoglobin.

37. Which statement about blood circulation in fish is FALSE?

[RRB Group D — 13 September 2022, Shift 1]

• (A) Ventricular blood flows towards the gills
• (B) Gills send oxygenated blood to the body
• (C) Blood from the body enters an atrium
• (D) A two-chambered heart produces double circulation

Answer: (D) A two-chambered heart produces double circulation

Explanation: Fish typically have a single circulatory circuit. Their two-chambered heart pumps oxygen-poor blood towards the gills, where it is oxygenated before travelling to body tissues. Blood then returns to the heart without passing through a separate pulmonary circuit as in mammals.

36. Which hormone raises the heartbeat in mammals during an emergency?

[UPSC NDA-II, General Ability Test — 4 September 2022]

• (A) Insulin
• (B) Melatonin
• (C) Thyroxine
• (D) Adrenaline

Answer: (D) Adrenaline

Explanation: Adrenaline, released by the adrenal medulla during stress, activates sympathetic responses. It raises heart rate and contractility and helps redirect blood flow towards actively responding tissues. This rapid fight-or-flight action differs from insulin’s glucose-lowering role or melatonin’s circadian regulation.

35. Which organism has a three-chambered heart?

[RRB Group D — 2 September 2022, Shift 2]

• (A) Bird
• (B) Frog
• (C) Fish
• (D) Human

Answer: (B) Frog

Explanation: Adult frogs possess two atria and one ventricle, giving a three-chambered heart. Fish generally have two main chambers, while birds and mammals have four. Amphibian circulation allows some mixing of oxygenated and deoxygenated blood within the single ventricle.

34. Which ABO blood group is traditionally known as the universal donor?

[RRB Group D — 30 August 2022, Shift 3]

• (A) A
• (B) B
• (C) AB
• (D) O

Answer: (D) O

Explanation: Within the ABO system, group O red cells lack both A and B surface antigens. When the Rh factor is also considered, O-negative red cells are the standard emergency universal donor type. Modern transfusion practice still requires careful compatibility testing whenever feasible.

33. Which statement about the circulatory system is incorrect?

[RRB Group D — 22 August 2022, Shift 3]

• (A) Hypertension results from constriction of veins
• (B) Platelets help clotting
• (C) Lymph is tissue fluid
• (D) Capillaries drain through vessels forming veins

Answer: (A) Hypertension results from constriction of veins

Explanation: Systemic arterial resistance is important in determining blood pressure; constriction of arteries and arterioles can increase it. Constriction of veins is not the standard explanation of hypertension. Platelets assist coagulation, and capillaries drain into venules that unite to form larger veins.

32. Which vitamin is involved in normal clotting of blood?

[WBCS (Executive) Prelims — 2022]

• (A) Vitamin A
• (B) Vitamin D
• (C) Vitamin B
• (D) Vitamin K

Answer: (D) Vitamin K

Explanation: Vitamin K is required to produce functionally active forms of several clotting proteins. When levels are inadequate, clot formation may be delayed and bleeding risk increases. Green leafy vegetables supply phylloquinone, one major dietary form of this fat-soluble vitamin.

31. The watery portion of blood containing salts and proteins is called ______.

[RRB NTPC CBT-II, Level 3 — 14 June 2022, Shift 1]

• (A) Platelets
• (B) Red blood cells
• (C) Plasma
• (D) White blood cells

Answer: (C) Plasma

Explanation: Plasma is the liquid portion of whole blood, consisting mostly of water together with salts, proteins, hormones and dissolved nutrients. It generally accounts for roughly fifty-five percent of total blood volume. Removing clotting factors from plasma produces serum, a related but distinct fluid.

30. Which of these animals has a four-chambered heart?

[RRB NTPC CBT-II, Level 6 — 9 May 2022, Shift 1]

• (A) Peacock
• (B) Seahorse
• (C) Frog
• (D) Fish

Answer: (A) Peacock

Explanation: Peacocks are birds, and birds possess two atria and two ventricles that keep oxygenated and deoxygenated blood separate. Frogs have a three-chambered heart, whereas most fish and seahorses have two principal chambers. Four-chambered hearts support efficient systemic oxygen delivery.

29. Rh incompatibility between mother and foetus can arise when the mother is ______ and the foetus is ______.

[RPSC RAS Prelims — 27 October 2021]

• (A) Rh-positive; Rh-negative
• (B) Rh-negative; Rh-positive
• (C) Rh-negative; Rh-negative
• (D) Rh-positive; Rh-positive

Answer: (B) Rh-negative; Rh-positive

Explanation: An Rh-negative pregnant person can develop anti-D antibodies after exposure to Rh-positive foetal red cells. In a subsequent sensitised pregnancy, these antibodies may cross the placenta and destroy foetal erythrocytes. Antenatal anti-D immunoglobulin markedly reduces this preventable risk.

28. How many chambers does the heart of a crocodile have?

[RRB NTPC CBT-I — 23 July 2021, Shift 2]

• (A) Six
• (B) Four
• (C) One
• (D) Two

Answer: (B) Four

Explanation: Crocodilians are unusual among reptiles because their hearts have four chambers, structurally separating right and left atria and ventricles. They also possess specialised connections that can shunt blood in particular conditions. Most non-crocodilian reptiles have incompletely divided ventricles.

27. On which date is World Blood Donor Day observed?

[RRB NTPC CBT-I — 23 July 2021, Shift 1]

• (A) 10 June
• (B) 14 June
• (C) 12 June
• (D) 16 June

Answer: (B) 14 June

Explanation: World Blood Donor Day is observed on 14 June, the birth anniversary of Karl Landsteiner. It promotes safe blood donation and recognises voluntary donors. Donated blood and its separated components are vital in treating severe blood loss and several haematological disorders.

26. For which discovery is Karl Landsteiner especially remembered?

[RRB NTPC CBT-I — 7 April 2021, Shift 1]

• (A) Research on the nervous system
• (B) Isolation of DNA
• (C) Identification of Zika virus
• (D) Classification of blood groups

Answer: (D) Classification of blood groups

Explanation: Karl Landsteiner established the basis of the ABO blood group system by identifying differences in red-cell antigens and corresponding serum reactions. His work made blood transfusions much safer and earned him the Nobel Prize in Physiology or Medicine in 1930.

25. Which statement about mammals is incorrect?

[RRB NTPC CBT-I — 6 April 2021, Shift 2]

• (A) Most have hair
• (B) Some mammals lay eggs
• (C) Their heart is three-chambered
• (D) Mammary glands nourish young

Answer: (C) Their heart is three-chambered

Explanation: Mammals generally have a four-chambered heart with fully separated pulmonary and systemic circulation. They characteristically possess hair and mammary glands. Although most give birth to live young, monotremes such as platypuses and echidnas lay eggs, making that statement accurate.

24. The commonly cited normal systolic blood pressure in adults is approximately ______.

[RRB NTPC CBT-I — 5 April 2021, Shift 1]

• (A) 110 mmHg
• (B) 120 mmHg
• (C) 80 mmHg
• (D) 130 mmHg

Answer: (B) 120 mmHg

Explanation: Systolic pressure is the maximum pressure recorded in arteries during ventricular contraction. A familiar illustrative blood-pressure reading is 120/80 mmHg, where 120 is systolic and 80 is diastolic. Clinical interpretation depends on repeat readings, patient circumstances and applicable guidelines.

23. Which glands help regulate blood pressure in the human body?

[RRB NTPC CBT-I — 19 March 2021, Shift 2]

• (A) Adrenal glands
• (B) Pituitary glands
• (C) Pancreas
• (D) Pineal gland

Answer: (A) Adrenal glands

Explanation: The adrenal glands secrete hormones involved in circulatory regulation. Aldosterone supports sodium and water retention, influencing blood volume, while adrenaline affects heart rate and vascular responses. Both mechanisms can alter arterial pressure as part of the body’s broader homeostatic systems.

22. Which of these cell types is NOT normally a constituent of human blood?

[RRB NTPC CBT-I — 14 March 2021, Shift 1]

• (A) Leucocyte
• (B) Lymphocyte
• (C) Monocyte
• (D) Chondrocyte

Answer: (D) Chondrocyte

Explanation: Leucocytes circulate in the blood, and lymphocytes and monocytes are particular leucocyte types. Chondrocytes are mature cells embedded in cartilage, where they maintain the cartilaginous matrix. They are not normal circulating components of human blood under healthy conditions.

21. Which vessel supplies blood from the main arterial circulation to the kidneys?

[RRB NTPC CBT-I — 22 February 2021, Shift 2]

• (A) Vena cava
• (B) Renal vein
• (C) Renal artery
• (D) Coronary artery

Answer: (C) Renal artery

Explanation: Each renal artery branches from the abdominal aorta to deliver blood to a kidney for filtration and tissue nourishment. Blood returns through the renal veins. Coronary arteries instead supply the heart muscle, while the venae cavae return systemic venous blood to the heart.

20. Which medium transports dissolved salts around the human body?

[RRB NTPC CBT-I — 16 February 2021, Shift 1]

• (A) Blood
• (B) Plasma only is a blood vessel
• (C) Haemoglobin alone
• (D) Oxygen gas

Answer: (A) Blood

Explanation: Blood transports dissolved mineral salts throughout the body, chiefly within its plasma component. Sodium, potassium and chloride ions support fluid balance, nerve conduction and muscle function. Haemoglobin mainly transports respiratory gases, not the full range of dissolved blood constituents.

19. What is the liquid component of human blood?

[SSC Junior Engineer (Mechanical) — 11 December 2020]

• (A) Plasma
• (B) White blood cells
• (C) Red blood cells
• (D) Platelets

Answer: (A) Plasma

Explanation: Plasma is the water-rich extracellular fluid portion of blood that keeps formed elements suspended. It carries albumin, globulins, fibrinogen, hormones, salts and metabolites. Serum differs because it is obtained after blood has clotted and lacks many active clotting factors.

18. Which statement about the rare Bombay blood group is NOT correct?

[SSC CPO Tier I — 11 December 2019, Shift 1]

• (A) A Bombay-group patient can safely receive ordinary group O blood
• (B) The phenotype was identified in 1952 by Y. M. Bhende
• (C) The H antigen is absent on red cells
• (D) A and B antigens are absent on red cells

Answer: (A) A Bombay-group patient can safely receive ordinary group O blood

Explanation: Individuals with the Bombay phenotype lack the H antigen required for normal ABO antigen expression and may produce anti-H antibodies. Ordinary group O red cells still carry H antigen, so these patients generally require Bombay-phenotype compatible blood, not routine group O units.

17. Which ABO blood group is traditionally described as the universal donor?

[SSC Junior Engineer (Civil) — 25 September 2019, Morning]

• (A) B
• (B) AB
• (C) O
• (D) A

Answer: (C) O

Explanation: Group O red cells lack A and B antigens, making them widely compatible within the ABO system. Considering Rh type as well, O-negative red cells are the preferred universal emergency donor product. Compatibility and cross-matching should still be performed whenever possible.

16. Which vessel carries oxygenated blood from the lungs back to the heart?

[SSC MTS — 22 August 2019, Shift 3]

• (A) Pulmonary vein
• (B) Aorta
• (C) Vena cava
• (D) Renal artery

Answer: (A) Pulmonary vein

Explanation: Pulmonary veins collect oxygen-rich blood from the lungs and empty into the left atrium. They are an exception to the usual rule that veins carry oxygen-poor blood. By definition, veins return blood towards the heart regardless of its oxygen content.

15. Which heart chamber receives oxygen-rich blood returning from the lungs?

[SSC MTS — 21 August 2019, Shift 2]

• (A) Left atrium
• (B) Right ventricle
• (C) Left ventricle
• (D) Right atrium

Answer: (A) Left atrium

Explanation: The left atrium receives oxygenated blood from pulmonary veins. It then directs the blood through the mitral valve into the left ventricle, which ejects it into the aorta. The right atrium instead receives deoxygenated systemic blood through the venae cavae.

14. Which organism has a two-chambered heart?

[SSC MTS — 19 August 2019, Shift 3]

• (A) Human
• (B) Monkey
• (C) Sparrow
• (D) Fish

Answer: (D) Fish

Explanation: Most fishes have one atrium and one ventricle as their two principal pumping chambers. Blood passes through a single circuit: heart to gills, then body, and back to heart. Birds and mammals possess four-chambered hearts with double circulation.

13. Which reptile possesses a four-chambered heart?

[SSC MTS — 19 August 2019, Shift 2]

• (A) Crocodile
• (B) King cobra
• (C) Chameleon
• (D) Turtle

Answer: (A) Crocodile

Explanation: Crocodilians possess anatomically separate right and left ventricles, unlike most other living reptiles, whose ventricles are not fully divided. This four-chambered structure supports effective separation of circulations, although crocodilians retain specialised vascular shunts associated with diving and other physiological states.

12. Who demonstrated systemic blood circulation through the action of the heart?

[SSC CHSL — 11 July 2019, Shift 2]

• (A) Florence Rena Sabin
• (B) Ernst Heinrich Weber
• (C) Antonie van Leeuwenhoek
• (D) William Harvey

Answer: (D) William Harvey

Explanation: William Harvey described the heart as a pump and established that blood circulates through the body rather than being continuously consumed by tissues. His 1628 work transformed cardiovascular physiology. Later microscopic observations of capillaries helped confirm the complete circulatory pathway.

11. Approximately how much oxygen is carried by 100 mL of normally oxygenated human blood?

[WBCS Prelims — 2018]

• (A) 40 mL
• (B) 10 mL
• (C) 20 mL
• (D) 30 mL

Answer: (C) 20 mL

Explanation: One gram of fully saturated haemoglobin binds approximately 1.34 mL of oxygen. With roughly 15 grams of haemoglobin per 100 mL of blood, oxygen capacity is near 20 mL. Most of this oxygen is haemoglobin-bound, not dissolved in plasma.

10. What is the approximate lifespan of a normal human red blood cell?

[WBCS Prelims — 2018]

• (A) 60 days
• (B) 120 days
• (C) 180 days
• (D) 240 days

Answer: (B) 120 days

Explanation: Mature red blood cells circulate for about 120 days before being removed mainly by macrophages in the spleen, liver and bone marrow. Their biconcave structure and flexible membrane help them traverse narrow vessels. Bone marrow continuously replaces ageing erythrocytes.

9. Oxygenated blood arriving from the lungs is received by the heart’s ______.

[UPSC NDA General Ability Test — 9 September 2018]

• (A) Left auricle
• (B) Left ventricle
• (C) Right auricle
• (D) Right ventricle

Answer: (A) Left auricle

Explanation: The left auricle, or left atrium, receives oxygen-rich blood through the pulmonary veins. It passes this blood to the left ventricle, which pumps it through the aorta to the body. The right side of the heart handles venous return and pulmonary delivery.

8. Who discovered the human blood group system?

[SSC MTS — 4 October 2017, Shift 2]

• (A) Karl Landsteiner
• (B) Joseph Monier
• (C) William Kelly
• (D) William Sturgeon

Answer: (A) Karl Landsteiner

Explanation: Karl Landsteiner identified fundamental differences among human red cells and serum that became the ABO blood group system. His discovery explained dangerous transfusion reactions and enabled systematic donor–recipient matching. He received the 1930 Nobel Prize in Physiology or Medicine.

7. Which of these is the traditional reference reading for normal adult blood pressure?

[SSC CPO Tier I — 3 July 2017, Shift 2]

• (A) 120/90 mmHg
• (B) 120/80 mmHg
• (C) 140/90 mmHg
• (D) 140/100 mmHg

Answer: (B) 120/80 mmHg

Explanation: The widely taught illustrative blood pressure is 120/80 mmHg, showing systolic pressure first and diastolic second. Systolic pressure reflects ventricular contraction and diastolic pressure ventricular relaxation. In clinical settings, normality is interpreted using measured readings and current guidelines.

6. For emergency red-cell transfusion when the patient’s group is unknown, which blood type is generally preferred?

[RPSC RAS Prelims 2015 (re-examination of 2013)]

• (A) O Rh-positive
• (B) O Rh-negative
• (C) AB Rh-negative
• (D) AB Rh-positive

Answer: (B) O Rh-negative

Explanation: O-negative red cells lack A, B and Rh-D antigens and are commonly used when an urgent transfusion cannot await full typing. This reduces major compatibility risks, but emergency transfusion still follows clinical protocols and testing should continue as soon as possible.

5. A patient with blood group A needs transfusion. His wife is O, brother AB, son A and daughter O. Who can donate compatible ABO red cells?

[RPSC RAS Prelims — 2013]

• (A) Wife and brother
• (B) Brother and son
• (C) Brother, son and daughter
• (D) Wife, son and daughter

Answer: (D) Wife, son and daughter

Explanation: A recipient with blood group A may receive ABO-compatible red cells from donors of group A or O. The wife and daughter are group O, while the son is group A. The brother’s group AB cells carry B antigen and are incompatible.

4. Parents with blood groups AB-positive and O-negative have two biological sons and one adopted son, whose groups are A-positive, B-positive and O-positive. Which son is adopted?

[UPSC CSE Prelims — 2011]

• (A) The O-positive son
• (B) The A-positive son
• (C) The B-positive son
• (D) Cannot be determined

Answer: (A) The O-positive son

Explanation: In ordinary ABO inheritance, an AB parent passes an A or B allele, while an O parent passes an O allele. Biological children can therefore have blood group A or B, but not O. The O-positive son must be the adopted child.

3. Why does excessive inhalation of carbon monoxide decrease oxygen delivery in the human body?

[UPSC CSE Prelims — 2010]

• (A) Carbon monoxide becomes carbon dioxide inside the body
• (B) Carbon monoxide binds haemoglobin much more strongly than oxygen
• (C) Carbon monoxide destroys haemoglobin’s chemical structure
• (D) Carbon monoxide directly disables the brain’s respiratory centre

Answer: (B) Carbon monoxide binds haemoglobin much more strongly than oxygen

Explanation: Carbon monoxide forms carboxyhaemoglobin by occupying oxygen-binding sites on haemoglobin with substantially greater affinity than oxygen. This lowers the oxygen-carrying capacity of blood and impairs tissue delivery. Severe exposure can cause neurological injury, cardiac problems and potentially fatal hypoxia.

2. How many times does a healthy person’s heart beat, on average, in one minute?

[Uttarakhand PCS Prelims — 2007]

• (A) 86 times
• (B) 98 times
• (C) 72 times
• (D) 64 times

Answer: (C) 72 times

Explanation: A commonly taught approximate resting adult heart rate is 72 beats per minute, although a healthy adult resting range is usually much wider. Heart rate changes with exercise, temperature, emotion, medication and physical conditioning. The cardiac pacemaker normally initiates each beat.

1. Which statement about blood in a healthy person is correct?

[UPSC CSE Prelims — 2002]

• (A) Veins are fewer than arteries and contain less blood
• (B) Blood cells constitute about 70% of blood volume
• (C) White blood cells are made only in lymph nodes
• (D) Platelets are more numerous than white blood cells

Answer: (D) Platelets are more numerous than white blood cells

Explanation: Normal blood typically contains roughly 150,000–450,000 platelets per microlitre but only about 4,000–11,000 white blood cells. Therefore platelets greatly outnumber leucocytes. Plasma forms approximately 55% of blood volume, and white cells arise primarily from bone marrow stem cells.