Body Fluids & Circulation: 50 Tricky MCQs (NCERT Class 11, With Answers)
1. Human blood transports crucial gases efficiently between the lungs and tissues despite having a closed circulatory system. What specialized substance in red blood cells allows this high efficiency of oxygen carriage and release under varying pH?
- (A) Fibrinogen
- (B) Platelets
- (C) Haemoglobin
- (D) Albumin
Answer: (C)
2. If a person loses a large amount of blood in a road accident, rapid replacement of which major component is initially essential to stabilize blood pressure and maintain circulation?
- (A) Erythrocytes
- (B) Plasma
- (C) Platelets
- (D) Lymphocytes
Answer: (B)
3. Which among the following describes the double circulation in humans, keeping in mind the routes and oxygen content in each chamber of the heart?
- (A) Blood passes twice through the right atrium with oxygenated blood
- (B) Blood flows once through the lungs and once through the body tissues in one complete cycle
- (C) Simultaneous mixing of oxygenated and deoxygenated blood in right ventricle
- (D) Pulmonary vein carries deoxygenated blood
Answer: (B)
4. There is a natural “pacemaker” embedded in the wall of the right atrium that ensures regular electrical impulses for heartbeats. What is the medical abbreviation for this vital structure?
- (A) AV node
- (B) SA node
- (C) Bundle of His
- (D) Purkinje fibers
Answer: (B)
5. A patient’s ECG shows abnormal delay between the contraction of atria and ventricles. Failure of which node would most likely result in this delay?
- (A) Sinoatrial node
- (B) Atrioventricular node
- (C) Purkinje fibers
- (D) Bundle of His
Answer: (B)
6. Clotting of blood is a complex process involving several plasma proteins. Which protein is converted into insoluble threads that form the meshwork of a clot?
- (A) Fibrinogen
- (B) Heparin
- (C) Thrombin
- (D) Albumin
Answer: (A)
7. The walls of ventricles are thicker than atria. Which function justifies this difference in thickness?
- (A) Atria act as main pump of the heart
- (B) Ventricles need to pump blood forcefully to lungs and rest of the body
- (C) Atria receive blood under high pressure
- (D) None of the above
Answer: (B)
8. In a healthy adult, what is the approximate average lifespan of a red blood cell (erythrocyte)?
- (A) 10 days
- (B) 60 days
- (C) 120 days
- (D) 365 days
Answer: (C)
9. During tissue metabolism, most of the carbon dioxide released diffuses into blood and is carried as:
- (A) Dissolved in plasma
- (B) Carbamino-hemoglobin
- (C) Bicarbonate ions
- (D) None of these
Answer: (C)
10. If a person’s blood group is AB+, what antibodies are present in his/her plasma under normal physiological conditions?
- (A) Anti-A
- (B) Anti-B
- (C) Both Anti-A and Anti-B
- (D) None
Answer: (D)
11. Which component of human blood plays the principal role in the immune response by producing antibodies?
- (A) Platelets
- (B) Neutrophils
- (C) Lymphocytes
- (D) Erythrocytes
Answer: (C)
12. A patient is found to have a lack of clotting factor VIII, leading to excessive and uncontrolled bleeding even from minor injuries. What is this condition called?
- (A) Thalassemia
- (B) Anaemia
- (C) Hemophilia
- (D) Leukemia
Answer: (C)
13. The human heart is unique among vertebrates for its complete separation of oxygenated and deoxygenated blood. Which chamber receives only oxygenated blood?
- (A) Right atrium
- (B) Left atrium
- (C) Right ventricle
- (D) Vena cava
Answer: (B)
14. Lymph differs from blood primarily in which of the following characteristics?
- (A) Higher oxygen content
- (B) Absence of white blood cells
- (C) Low protein and RBC content
- (D) It does not transport fatty acids
Answer: (C)
15. If a tricuspid valve is not functioning properly, which event is most affected?
- (A) Blood flow from left atrium to left ventricle
- (B) Blood flow from right atrium to right ventricle
- (C) Blood flow from right ventricle to lungs
- (D) Blood flow from body to right atrium
Answer: (B)
16. Blood pressure is usually measured in which artery, and why is this artery chosen?
- (A) Femoral artery, easily accessible
- (B) Brachial artery, superficial and close to heart
- (C) Carotid artery, gives pulse directly to brain
- (D) Renal artery, represents systemic pressure
Answer: (B)
17. What abnormality characterizes atherosclerosis and can lead to ischemic heart diseases?
- (A) Calcium deposition in veins
- (B) Fat and cholesterol build up in artery walls
- (C) Formation of excessive RBCs
- (D) Low sodium in plasma
Answer: (B)
18. In cardiac physiology, what is referred to as “systole”?
- (A) Relaxation of ventricles
- (B) Contraction of atria or ventricles
- (C) Opening of heart valves only
- (D) None of these
Answer: (B)
19. Which blood component is responsible for the transport of most carbon dioxide in human blood?
- (A) Plasma as bicarbonate ions
- (B) Erythrocytes as carbamino-hemoglobin
- (C) Platelets as CO2 carriers
- (D) Lymphocytes as gas exchangers
Answer: (A)
20. A newborn turns yellow in skin color within a few days of birth. This is most likely due to excess bilirubin in blood as a result of:
- (A) Persistent fetal hemoglobin
- (B) Rapid breakdown of fetal RBCs
- (C) High blood oxygen
- (D) Excess plasma proteins
Answer: (B)
21. Capillaries have unique thin walls made of:
- (A) Single layer of squamous epithelium
- (B) Multiple muscle layers
- (C) Elastic tissue and valves
- (D) Dense connective tissue
Answer: (A)
22. Which one of the following carries oxygenated blood in the adult human body?
- (A) Pulmonary artery
- (B) Pulmonary vein
- (C) Superior vena cava
- (D) Right atrium
Answer: (B)
23. Which chamber of the human heart receives deoxygenated blood from the whole body?
- (A) Right atrium
- (B) Right ventricle
- (C) Left atrium
- (D) Left ventricle
Answer: (A)
24. The correct average values for hemoglobin and total blood volume in a healthy adult male are:
- (A) 12-16g/dL; 3L
- (B) 14-18g/dL; 5-6L
- (C) 5-10g/dL; 2L
- (D) 15-20g/dL; 10L
Answer: (B)
25. What major role do platelets play in the body’s internal defense system?
- (A) Carry oxygen to tissues
- (B) Initiate blood clotting
- (C) Regulate osmosis in blood
- (D) Neutralize toxins
Answer: (B)
26. The “lub-dub” sound in the heart is mainly produced by:
- (A) Contraction of heart muscles
- (B) Closing of heart valves
- (C) Flow of blood through arteries
- (D) Opening of tricuspid valve
Answer: (B)
27. Which blood vessel is the main supplier of oxygenated blood to the lower half of the human body?
- (A) Pulmonary vein
- (B) Inferior vena cava
- (C) Aorta
- (D) Subclavian artery
Answer: (C)
28. During intense physical exercise, the cardiac output increases mainly by:
- (A) Increasing heart rate and stroke volume
- (B) Decreasing blood viscosity
- (C) Expanding arterial walls
- (D) Opening the foramen ovale
Answer: (A)
29. In human circulation, which vein uniquely carries oxygenated blood?
- (A) Pulmonary vein
- (B) Hepatic portal vein
- (C) Renal vein
- (D) Subclavian vein
Answer: (A)
30. Which of the following is NOT a direct function of plasma proteins?
- (A) Clotting of blood
- (B) Transportation of hormones
- (C) Immunity
- (D) Synthesis of hemoglobin
Answer: (D)
31. Which term describes the condition when a blood clot forms inside a blood vessel and may obstruct blood flow?
- (A) Anemia
- (B) Thrombosis
- (C) Leukemia
- (D) Polycythemia
Answer: (B)
32. The normal diastolic blood pressure (in mm Hg) in a healthy adult is:
- (A) 90
- (B) 120
- (C) 80
- (D) 60
Answer: (C)
33. When plasma without clotting factors is separated from blood, what is that clear fluid called?
- (A) Serum
- (B) Lymph
- (C) Myoglobin
- (D) Interstitial fluid
Answer: (A)
34. Which chemical is most responsible for causing vasodilation and drop in blood pressure during allergic reactions?
- (A) Fibrinogen
- (B) Thrombin
- (C) Histamine
- (D) Hemoglobin
Answer: (C)
35. The pulmonary artery is exceptional among arteries, as it carries:
- (A) Oxygenated blood away from heart
- (B) Deoxygenated blood away from heart
- (C) Lymph to lungs
- (D) Oxygenated blood to tissues
Answer: (B)
36. Which instrument is commonly used to measure arterial blood pressure in humans?
- (A) Spirometer
- (B) Sphygmomanometer
- (C) Electrocardiogram
- (D) Stethoscope
Answer: (B)
37. In the heart, the pacemaker sends electrical impulses at a normal rate of:
- (A) 20-30 per minute
- (B) 40-50 per minute
- (C) 70-75 per minute
- (D) 100-120 per minute
Answer: (C)
38. Which physiological mechanism prevents the backflow of blood in veins?
- (A) Muscular wall thickness
- (B) Semilunar valves
- (C) Smooth muscle contraction only
- (D) Capillary sphincters
Answer: (B)
39. Which protein increases in concentration during infection and helps in destroying viruses and bacteria?
- (A) Albumin
- (B) Globulins
- (C) Fibrinogen
- (D) Collagen
Answer: (B)
40. What is the chief benefit of capillary beds in tissues?
- (A) Permit rapid blood flow for pressure regulation
- (B) Increase surface area for exchange of gases and nutrients
- (C) Store extra fluid during dehydration
- (D) Prevent clotting
Answer: (B)
41. During a cardiac cycle, what event signifies the start of ventricular diastole?
- (A) Closure of semilunar valves
- (B) Opening of tricuspid valve
- (C) Closure of bicuspid valve
- (D) Contraction of left atrium
Answer: (A)
42. Which hormone stimulates the production of red blood cells in the bone marrow?
- (A) Thrombopoietin
- (B) Erythropoietin
- (C) Renin
- (D) Insulin
Answer: (B)
43. The term “hematocrit” refers to:
- (A) Volume of plasma in blood
- (B) Percentage of RBCs in blood
- (C) Number of platelets in a microliter of blood
- (D) Volume of lymph in circulation
Answer: (B)
44. Which circulatory change does fetal circulation have that is not present in adults?
- (A) Presence of ductus arteriosus
- (B) Direct connection between left and right atria via foramen ovale
- (C) Both (A) and (B)
- (D) None of the above
Answer: (C)
45. Which structure collects lymph from the lower half of the body and empties it into the venous system?
- (A) Subclavian vein
- (B) Thoracic duct
- (C) Right lymphatic duct
- (D) Jugular vein
Answer: (B)
46. Which of the following statements is correct about venous blood?
- (A) Always oxygenated
- (B) Always deoxygenated
- (C) May be either, but in pulmonary vein is oxygenated
- (D) Carries only nutrients
Answer: (C)
47. Which part of the circulatory system’s automatic nerves decreases the heart rate?
- (A) Sympathetic nervous system
- (B) Parasympathetic nervous system
- (C) Somatic nervous system
- (D) Central nervous system
Answer: (B)
48. Which electrolyte (ion) is essential in converting prothrombin to thrombin during coagulation?
- (A) Fe2+
- (B) Na+
- (C) Ca2+
- (D) K+
Answer: (C)
49. What causes anemia in a person?
- (A) Decreased number of WBCs
- (B) Decreased hemoglobin content
- (C) Increase in plasma proteins
- (D) Excessive clot formation
Answer: (B)
50. When a person ascends quickly to a high altitude, what is one primary short-term effect on their circulatory system?
- (A) Lowering of cardiac output
- (B) Increased production of red blood cells
- (C) Decreased heart rate
- (D) No change in blood composition
Answer: (B)
🧾 Answer Key – 50 MCQs (Body Fluids & Circulation, NCERT)
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