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Biology MCQ, Class-12, Chapter-8, Microbes in Human Welfare
NCERT Based MCQ with Explanation:
1. Which of the following is not a component of blood plasma?
(a) Fibrinogen
(b) Lymphocytes
(c) Albumins
(d) Globulins
Explanation: Lymphocytes are formed elements (cells) found in blood, not a component of plasma. Plasma primarily contains water, proteins (fibrinogen, albumins, and globulins), and dissolved substances.
2. What is the average life span of human erythrocytes?
(a) 60 days
(b) 90 days
(c) 120 days
(d) 180 days
Explanation: Erythrocytes, or red blood cells, have an average lifespan of 120 days, after which they are destroyed in the spleen.
3. Which plasma protein is primarily responsible for blood clotting?
(a) Albumin
(b) Fibrinogen
(c) Globulin
(d) Hemoglobin
Explanation: Fibrinogen is a key protein involved in the coagulation of blood, forming fibrin threads that create a clot.
4. Which blood group is known as the universal donor?
(a) A
(b) B
(c) AB
(d) O
Explanation: Blood group O lacks A and B antigens, so it can be donated to individuals of any blood type.
5. What is the function of basophils in the body?
(a) Oxygen transport
(b) Blood clotting
(c) Secretion of histamine
(d) Phagocytosis
Explanation: Basophils secrete histamine, serotonin, and heparin, playing a role in inflammatory reactions.
6. Which heart valve prevents backflow of blood from the left ventricle to the left atrium?
(a) Tricuspid valve
(b) Pulmonary valve
(c) Bicuspid (Mitral) valve
(d) Aortic valve
Explanation: The bicuspid valve is located between the left atrium and left ventricle and prevents backflow during ventricular contraction.
7. What is the primary function of lymph?
(a) Transport of respiratory gases
(b) Absorption of fats
(c) Regulation of blood pressure
(d) Destruction of pathogens
Explanation: Lymph absorbs fats from the digestive tract through the lacteals and is also involved in immune responses.
8. Which of the following is true about the sino-atrial node (SAN)?
(a) It generates action potentials at the lowest rate.
(b) It is located in the left atrium.
(c) It acts as the pacemaker of the heart.
(d) It contracts the ventricles directly.
Explanation: The SAN generates the highest rate of action potentials (70–75 per minute) and initiates the heart's rhythmic activity.
9. What is the average cardiac output of a healthy individual?
(a) 2 liters/min
(b) 3 liters/min
(c) 5 liters/min
(d) 7 liters/min
Explanation: Cardiac output is the product of stroke volume and heart rate, averaging around 5 liters per minute in a healthy adult.
10. Which of the following conditions is characterized by the narrowing of coronary arteries?
(a) Angina
(b) Hypertension
(c) Atherosclerosis
(d) Heart failure
Explanation: Atherosclerosis involves the deposition of plaques in the coronary arteries, leading to reduced blood flow to the heart muscle.
11. Which formed element is involved in blood clotting?
(a) Erythrocytes
(b) Platelets
(c) Lymphocytes
(d) Neutrophils
Explanation: Platelets (thrombocytes) are cell fragments essential for blood clotting. They release substances that promote coagulation.
12. Which blood group lacks both A and B antigens?
(a) A
(b) B
(c) AB
(d) O
Explanation: Blood group O lacks A and B antigens on red blood cells, making it the universal donor.
13. What is the normal range of white blood cell (WBC) count in humans?
(a) 4,000–6,000 mm³
(b) 6,000–8,000 mm³
(c) 8,000–10,000 mm³
(d) 10,000–12,000 mm³
Explanation: A healthy adult typically has 6,000–8,000 white blood cells per cubic millimeter of blood.
14. Which type of WBC is primarily responsible for allergic reactions?
(a) Neutrophils
(b) Eosinophils
(c) Monocytes
(d) Lymphocytes
Explanation: Eosinophils combat allergies and parasitic infections by releasing histamines and other chemicals.
15. What does the P-wave in an ECG represent?
(a) Ventricular depolarization
(b) Atrial depolarization
(c) Atrial repolarization
(d) Ventricular repolarization
Explanation: The P-wave indicates the electrical excitation of the atria, leading to their contraction.
Science MCQ, Class 9th, Chapter-13, Why Do We Fall Ill?16. The hepatic portal system connects which two organs?
(a) Heart and lungs
(b) Liver and intestines
(c) Kidneys and bladder
(d) Brain and spinal cord
Explanation: The hepatic portal vein carries blood from the intestines to the liver for processing before it enters systemic circulation.
17. Which of the following valves is located between the right atrium and the right ventricle?
(a) Mitral valve
(b) Tricuspid valve
(c) Aortic valve
(d) Pulmonary valve
Explanation: The tricuspid valve prevents backflow of blood from the right ventricle to the right atrium.
18. What is the primary function of lymphocytes?
(a) Gas transport
(b) Immune response
(c) Blood clotting
(d) Protein synthesis
Explanation: Lymphocytes, including B and T cells, are vital for the body’s defense against pathogens.
19. Which ion plays a crucial role in the blood clotting process?
(a) Sodium
(b) Potassium
(c) Calcium
(d) Magnesium
Explanation: Calcium ions are necessary for the activation of clotting factors during the coagulation cascade.
20. What is the primary cause of erythroblastosis fetalis?
(a) ABO incompatibility
(b) Rh incompatibility
(c) Low platelet count
(d) High WBC count
Explanation: Erythroblastosis fetalis occurs when an Rh-negative mother carries an Rh-positive fetus, leading to the formation of maternal antibodies against the fetal blood.
21. Which type of circulation is observed in fish?
(a) Single circulation
(b) Double circulation
(c) Pulmonary circulation
(d) Systemic circulation
22. What happens during ventricular systole?
(a) Atria contract, and ventricles relax.
(b) Ventricles contract, pushing blood into the arteries.
(c) Atria and ventricles both contract simultaneously.
(d) Atria relax, filling the ventricles.
23. What triggers the initiation of the cardiac cycle?
(a) Atrial contraction
(b) Ventricular relaxation
(c) Action potential generated by the SAN
(d) Closure of semilunar valves
24. What is the significance of the atrioventricular node (AVN)?
(a) It pumps blood into the ventricles.
(b) It delays the action potential from the SAN to ensure proper ventricular filling.
(c) It generates the action potential for ventricular contraction.
(d) It prevents backflow of blood.
25. Which of the following cells are phagocytic in nature?
(a) Eosinophils and basophils
(b) Neutrophils and monocytes
(c) Lymphocytes and erythrocytes
(d) Platelets and thrombocytes
26. Which valve prevents backflow of blood from the pulmonary artery into the right ventricle?
(a) Tricuspid valve
(b) Mitral valve
(c) Aortic valve
(d) Pulmonary valve
27. What is the primary function of the hepatic portal vein?
(a) Transport oxygenated blood to the liver
(b) Carry deoxygenated blood from the liver to the heart
(c) Transport nutrient-rich blood from the intestine to the liver
(d) Drain lymph from the liver to the vena cava
28. What is the purpose of coronary circulation?
(a) To supply blood to the lungs
(b) To supply blood to the digestive system
(c) To provide oxygen and nutrients to the heart muscle
(d) To transport hormones to the heart
29. What is the average stroke volume in a healthy adult?
(a) 50 mL
(b) 70 mL
(c) 90 mL
(d) 120 mL
30. Which structure is known as the "graveyard of RBCs"?
(a) Liver
(b) Bone marrow
(c) Spleen
(d) Lymph nodes
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