Biology Question Bank – 54 MCQs on “Circulatory System and Immunity” – Answered!

(b) cow

(c) camel

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(d) cockroach.

Answer and Explanation:

1. (b): RBCs do not occur in the blood of cockroach. The circulatory system of cockroach is of open type. Viscera lie in the haemocoel immersed in blood called haemolymph. The latter consists of colourless plasma and irregular white corpuscles, the leucocytes. There are no blood vessels except aorta that carries blood from the heart to the haemocoel.

2. Breakdown product of haemoglobin is

(a) bilirubin

(b) iron

(c) biliverdin

(d) calcium.

Answer and Explanation:

2. (a, b): The haemoglobin is broken down into haem i.e. iron and globin protein which is then converted into yellowish substance bilirubin which is extracted by the liver cells from the blood and stored in the form of bile in gall bladder.

3. Child death may occur in the marriage of

(a) Rh+ man and Rh’ woman

(b) Rh man and Rli woman

(c) Rh man and Rh woman

(d) Rh man and Rh’ woman.

Answer and Explanation:

3. (b): Rh factor plays a crucial role in child’s birth born out of a marriage between Rh woman and a Rh- man. In such a case, the mother becomes sensitive while carrying a first Rh+ child within her womb. The reason for such sensitivity is that some of the RBCs from the developing embryo get into the blood stream of the mother during development, causing her to produce anti-Rh antibodies.

In fact, the first child of such parents is nearly normal and is delivered safely. However, if such a mother gets pregnant again, the subsequent Rh+ foetuses will be exposed to the anti-Rh antibodies produced by the mother. As a result serious damage to the red blood cells of the developing embryo will occur causing haemolytic disease of the newborn (HDN) or erythroblastosis foetalis. This disease leads to the death of the developing embryo before birth or after parturition.

4. Presence of RBC in urine is

(a) alkaptonuria

(b) urothiasis

(c) hematuria

(d) proteinuria.

Answer and Explanation:

4. (c): Presence of RBCs in the blood is known as hematuria. Alkaptonuria is the excretion of large amount of alkapton in urine which when comes in contact with light turns black. Proteinuria is the presence of proteins in the blood.

5. Sickle cell disease is characterised by

(a) leukemia

(b) polycythemia

(c) mental retardation

(d) hemolytic anaemia.

Answer and Explanation:

5. (d): Sickle cell disease is a generic term for a group of genetic disorders characterized by the predominance of hemoglobin S (Hb S). These disorders include sickle cell anemia, the sickle beta thalassemia syndromes, and hemoglobinopathies in which Hb S is in association with another abnormal hemoglobin that not only can participate in the formation of hemoglobin polymers but also is present in sufficient concentration to enable the red cells to sickle.

There are two cardinal pathophysiologic features of sickle cell disorders: chronic hemolytic anemia and vasoocclusion (which results in ischemic tissue injury). Hemolytic anemia may be related to repeated cycles of sickling and unsickling, which interact to produce irreversible red cell membrane changes, red cell dehydration, and erythrocyte destruction. Tissue injury is usually produced by hypoxia secondary to the obstruction of blood vessels by an accumulation of sickled erythrocytes.

6. Haemophilia is

(a) royal disease

(b) faulty blood clotting

(c) both a and b

(d) mosquito having haemocoel.

Answer and Explanation:

6. (a): Haemophilia disease (Royal Disease) has been | quite common in the royal families of Europe. The disease spread to them through the children of Queen Victoria.

The ancestors of the queen did not possess the disease, j It appears that the gene for haemophilia developed either in the germ cells of her father or herself through mutation. : Haemophilia is sex-linked disease which is also known as bleeder’s disease as the patient continues to bleed even from a minor cut since he or she does not possess the natural phenomenon of blood clotting due to absence of antihaemophiliac globulin or factor VIII (haemophilia- A) and plasma thromboplastin factor IX (haemophilia-B. Christmas disease) essential for it. As a result of continuous bleeding, the patient may die of blood loss.

There is no permanent cure of the disease. Haemophilia (= hemophilia) is genetically due to the presence of a recessive sex linked gene h, carried by X- chromosome.

7. Which one engulfs pathogens rapidly?

(a) acidophils

(b) monocytes

(c) basophils

(d) neutrophils.

Answer and Explanation:

7. (d): Neutrophils, are the most abundant type of white blood cells and form an integral part of the immune system. These phagocytes are normally found in the blood stream. However, during the acute phase of inflammation, particularly as a result of bacterial infection, neutrophils leave the vasculature and migrate toward the site of inflammation in a process called chemotaxis.

They are the predominant cells in pus, accounting for its whitish/ yellowish appearance. Neutrophils react within an hour of tissue injury and are the hallmark of acute inflammation. Monocytes are also phagocytes but take 7-8 hours to reach at the site of iiijuryvAcidophils and basophils are not phagocytic in nature.

8. Tricuspid valve is found in between

(a) sinus venosus and right auricle

(b) right auricle and right ventricle

(c) left ventricle and left auricle

(d) ventricle and aorta.

Answer and Explanation:

8. (b): The right auricle opens into the right ventricle through a wide passage, the right auriculoventricular or

A-V aperture. This aperture is guarded by a one-way valve called the tricuspid valve. The valve consists of three membranous flaps which are attached to the margin of the right auriculoventricular aperture above but project freely into the ventricle below. Their free lower edges are fixed to the papillary muscles of the right ventriele by a number of tough, white cords, the chordae tendineae.

9. A person with blood group A requires blood. The blood group which can be given is

(a) A and B

(b) A and AB

(c) A and O

(d) A, B, AB and O.

Answer and Explanation:

9. (c): Karl Landsteiner recognized four types of blood groups in human beings. The ABO blood groups are determined by the gene I having three alleles (1A, 1B and 1°) In human beings, there are present two antigens A and B produced by 1A and 1B alleles respectively. These antigens are always present on the surface of red blood cells.

Also are present two antibodies in the plasma anti A and anti B Blood group A has antigen A and antibody B so a person having this blood group can receive blood from the person having the same blood group. Persons with blood group O have no antigens on the surface of RBCs but have both the antibodies in the plasma. Hence, these can donate blood to anyone (universal donors). However, such persons can receive blood only from those persons who have blood group O.

10. Removal of calcium from freshly collected blood would

(a) cause delayed clotting

(b) prevent clotting

(c) cause immediate clotting

(d) prevent destruction of haemoglobin.

Answer and Explanation:

10. (b): Thromboplastin, a lipoprotein, helps in clot formation. Thromboplastin helps in the formation of an enzyme prothrombinase. This enzyme inactivates heparin and it also converts the inactive plasma protein prothrombin into its active form, thrombin. Both the changes require calcium ions. Thrombin converts fibrinogen molecule to insoluble fibrin.

The fibrin monomers polymerize to form long, sticky fibres. The fibrin threads form a fine network over the wound and trap blood corpuscles (RBCs, WBCs, platelets) to form a crust, the clot. Thus, if calcium is removed from the blood, clotting process will not occur.

11. Arteries carry oxygenated blood except

(a) pulmonary

(b) cardiac

(c) hepatic

(d) systemic.

Answer and Explanation:

11. (a): Pulmonary artery carries the blood from the right ventricle of the heart to the lungs for oxygenation so it carries deoxygenated blood.

12. A vein possesses a large lumen because

(a) tunica media and tunica externa form a single coat

(b) tunica interna and tunica media form a single coat

(c) tunica interna, tunica nicuiu and tunica externa are thin

(d) tunica media is a thin coat.

Answer and Explanation:

12. (d): Wall of a vein consists of tunic externa, tunic media and tunica interna. All these layers are also present in the wall of artery. However, in the wall of a vein, the elastic membrane of tunica interna is relatively thin, and muscle fibres and elastic fibres in tunica media are fewer. Therefore, a vein has a thinner and less elastic wall but a wider cavity than an artery of the same diameter.

13. Splenic artery arises from

(a) anterior mesenteric artery

(b) coeliac artery

(c) posterior mesenteric artery

(d) intestinal artery.

Answer and Explanation:

13. (b): The splenic artery is the blood vessel that supplies oxygenated blood to the spleen. It branches from the coeliac artery, and follows a course superior to the pancreas. The coeliac artery is the first major branch of the abdominal aorta and branches from the aorta around the level of the T12 vertebra in humans. It is one of three anterior/ midline branches of the abdominal aorta.

14. Wall of blood capillary is formed of

(a) haemocytes

(b) parietal cells

(c) endothelial cells

(d) oxyntic cells.

Answer and Explanation:

14. (c): The wall of capillaries is very thin (usually less than one micron) and have numerous minute pores and made up of only endothelium. Exchange-of material takes place between blood and tissue fluid across the endothelial membrane of capillaries through active diffusion.

The wall of blood vessels (arteries and veins) is made up of mainly 3 layers – the outer external has connective tissue, collagen fibres, lymph vessels and the middle tunica media has circular smooth muscle fibres some elastic fibres and the inner most tunica interna in a single layered endothelium of polyhedral squamous cells. If the arteries reach organs they form arterioles which are thinner and mainly consist smooth muscles and when they subdivide in the tissues they make capillaries.

15. Carbonic anhydrase occurs in

(a) lymphocytes

(b) blood plasma

(c) RBC

(d) leucocytes.

Answer and Explanation:

15. (c): During transport of CO, in the blood, about 70% of CO, released by respiring tissue cells is transported as bicarbonate ions. It diffuses into the plasma and then into the RBCs. Here, CO combines with water to form carbonic acid. This reaction is catalyzed by a zinc containing enzyme carbonic anhydrase. Carbonic- acid dissociates into bicarbonate and hydrogen ions. A small amount of bicarbonate ions is transported in the RBCs, whereas most of them diffuse into the plasma to be carried by it.

16. Blood group AB has

(a) no antigen

(b) no antibody

(c) neither antigen nor antibody

(d) both antigen and antibody.

Answer and Explanation:

16. (b): ABO blood groups are determined by the gene I (isoagglutinin). There are three alleles, 1A, 1B and 1° of this gene. Proteins produced by the IA and IB alleles are called A antigen and B antigen. People with blood group A have the A antigen on the surface of their RBCs, and antibodies to antigen B in their plasma.

Persons with blood group B have B antigen on their RBCs, and antibodies against A antigen in their plasma, individuals with AB blood group have both antigen A and antigen B on their RBCs, and no antibodies for either of the antigens in their plasma. Type O individuals are without A and B antigens on their RBCs, but have antibodies for both these antigens in their plasma.

18. Cells formed in bone marrow include

(a) RBC

(b) RBC and leucocytes

(c) leucocytes

(d) lymphocytes.

Answer and Explanation:

18. (b): In the embryo and foetal stage of vertebrates, RBCs and leucocytes are formed in the bone marrow, lymph nodes, yolk sac, liver, spleen and thymus but after birth they are formed in red bone marrow only.

19. Blood capillaries are made of

(a) endothelium, connective tissue and muscle fibres

(b) endothelium and muscle fibres

(c) endothelium and connective tissue

(d) endothelium only.

Answer and Explanation:

19. (b): Refer answer 14.

20. Cells involved in immune mechanism are

(a) erythrocytes

(b) lymphocytes

(c) eosinophils

(d) thrombocytes.

Answer and Explanation:

20. (b): The resistance that an individual acquires during life, is called acquired immunity. Two major groups of cells are involved in acquired immunity: lymphocytes and antigen presenting cells. A healthy person has about a trillion lymphocytes. Lymphocytes are of two types: T lymphocytes or T cells and B lymphocytes or B cells. Both types of lymphocytes and other cells of the immune system are produced in the bone marrow.

21. The pace setter in the heart is called

(a) sino-atrial node (SAN)

(b) atrio-ventricular node (AVN)

(c) Purkinje fibres

(d) papillary muscle.

Answer and Explanation:

21. (b): AV (atrioventricular) node is a mass of modified heart muscle situated in the lower middle part of the right atrium. It receives the impulse to contract from the SA node via the atria and transmits it through the atrioventricular bundles to the ventricles. AV node is called the pace setter. Here, the impulses are delayed for 0.1 second to ensure that the auricles will contract first and empty fully before the ventricles contract.

22. The heart sound dup is produced when

(a) mitral valve is closed

(b) semi-lunar valves at the base of aorta get closed

(c) tricuspid valve is opened

(d) mitral valve is opened.

Answer and Explanation:

22. (b): The “dup” sound is produced by the closure of the semilunar valves at the start of ventricular relaxation. It lasts for 0.1 seconds and its principle frequency is 50 cycles/sec. It is higher pitched, louder, sharper and of short duration as compared to ‘lub’. The semilunar valves close to prevent any backflow of blood from aorta to the ventricles.

23. The main reason why antibodies could not solve all the problems of bacteria mediated disease is

(a) decreased efficiency of the immune system

(b) insensitivity of the individual following prolonged exposure to antibiotics

(c) development of mutant strains resistant to antibodies

(d) inactivation of antibiotics by bacterial enzymes.

Answer and Explanation:

23. (c): Bacteria develop mutant strains that become resistant to antibodies, so these antibodies become incapable of removing bacteria mediated diseases.

24. Antigens are present

(a) inside the cytoplasm

(b) on nuclear membrane

(c) inside the nucleus

(d) on cell surface.

26. In veins, valves are present to check backward flow of blood flowing at

(a) atmospheric pressure

(b) high pressure

(c) low pressure

(d) all of these.

Answer and Explanation:

26. (c): Veins carry blood at low pressure as compared to blood carried by arteries. Arteries carry blood from the heart whose function is to pump blood at high pressure so that blood can reach each and every part of the body. Veins carry blood from tissues to the heart, so they carry blood at low pressure. Valves are present in the veins to prevent backflow of flood due to force of gravity.

27. The lymph serves to

(a) return the interstitial fluid to the blood

(b) return the WBCs and RBCs to the lymph nodes

(c) transport CO2 to the lungs

(d) transport O2 to the brain.

Answer and Explanation:

27. (a): Lymph (also called tissue fluid in the intercellular spaces) is the colourless liquid found within the lymphatic system. An important function of lymph is to return interstitial fluid back to the blood.

The interstitial fluid is the filtered form of the blood without the cellular components and plasma proteins. It consists of water containing dissolved materials. It receives CO2, nitrogenous waste products, hormones and other synthetic substances from the tissue cells and enters the lymph capillaries to discharge them into blood.

28. The correct route through which pulse-making impulse travels in the heart is

(a) SA node —> Purkinje fibres —> bundle of His —> AV node —> heart muscles

(b) SA node —> AV node —> bundle of His —> Purkinje fibres —> heart muscles

(c) AV node —> bundle of His —> SA node —> Purkinje fibres —> heart muscles

(d) AV node —> SA node —> Purkinje fibres —> bundle of His —> heart muscles.

Answer and Explanation:

28. (b): The heart beat results from an action potential generated at SA node which is located in the wall of the right auricle. The wave of depolarization is then passed to AV node, located in the wall between the right auricle and right ventricle.

The bundle of His originates from AV node and passes downward, dividing into the right and left bundle branches, one going into the wall of each ventricle. In the walls, the two branches break up into a large number of Purkinje fibres that are distributed to the entire musculature of the ventricles. This shows that the pulse making impulse travels in the heart in the following order.

29. Antibodies are produced by

(a) leucocytes

(b) monocytes

(c) lymphocytes

(d) spleen.

Answer and Explanation:

29. (c): Lymphocytes [type of leucocytes (WBCs)] secrete antibodies to destroy microbes and their toxins, reject grafts and kill tumor cells. Antibodies are protein in nature. Monocytes (type of WBC) is phagocytic in nature and engulf bacteria and cellular debris. Spleen is an organ that produces lymphocytes.

30. The interferons are

(a) antigen proteins

(b) antiviral proteins

(c) antibiotic proteins

(d) all of these.

Answer and Explanation:

30. (b): Interferons are antiviral proteins that increase the resistance of a cell to attack by viruses. In humans, three groups of interferons have been discovered: a- interferons from WBCs, P-interferons from connective tissue fibroblasts and y-interferons from lymphocytes.

31. Which of the following is the false statement about “antibiotics”?

(a) some persons have allergy from antibiotics

(b) antibiotics are capable of curing any disease

(c) this term was given by Waksman in 1942

(d) antibiotics is produced by micro-organisms.

Answer and Explanation:

31. (b): Antibiotics are not capable of curing any disease. Antibiotics are those substances that destroy or inhibit the growth of micro-organisms, particularly disease producing bacteria and fungi. The term antibiotic was introduced by Waksman in 1942. Antibiotics are obtained from micro-organisms (especially moulds) or synthesized. Common antibiotics include penicillins, streptomycin and tetracyclines. They are used to treat various infections but tend to weaken the body’s natural defence mechanisms and can cause allergies. Overuse of antibiotic can lead to the development of resistant strains of micro-organism.

32. If a person shows production of interferons in his body, the chances are that he has got an infection of

(a) tetanus

(b) malaria

(c) typhoid

(d) measles.

Answer and Explanation:

32. (d): Interferons are antiviral proteins that increase the resistance of a cell to attack by viruses. As measles is a viral disease, so body produces interferons. Measles is an acute infectious eruptive viral disease of childhood, caused by an RNA containing Rubeola virus/Polynosa morbillorum. Typhoid and tetanus are bacterial diseases caused by Salmonella typhi and Clostridium tetani respectively. Malaria is a protozoan disease caused by Plasmodium species.

33. An adult human with average health has systolic and diastolic pressures as

(a) 120 mm Hg and 80 mm Hg

(b) 50 mm Hg and 80 mm Hg

(c) 80 mm Hg and 80 mm Hg

(d) 70 mm Hg and 120 mm Hg.

Answer and Explanation:

33. (a): The temporary rise in blood pressure during the contraction of the heart is called systolic pressure and the temporary fall in blood pressure during relaxation of the heart is called diastolic pressure. Blood pressure is expressed as the ratio of the systolic pressure over the diastolic pressure. For a healthy resting adult person, the average systolic/diastolic pressures are 120/80 mm Hg.

34. The thickening of walls of arteries is called

(a) arteriosclerosis

(b) arthritis

(c) aneurysm

(d) both (b) and (c).

Answer and Explanation:

34. (a): Arteriosclerosis is the hardening of arteries and arterioles due to thickening of the fibrous tissue, and the consequent loss of elasticity. In this disease, calcium salts precipitate with the cholesterol. This calcification ultimately makes the wall of arteries stiff and rigid. Arthritis is the inflammation of one or more joints, characterised by swelling, warmth, redness of the overlying skin, pain and restriction of motion. Aneurysm is a balloon like swelling in the wall of an artery due to degenerative disease or infection.

35. The antibodies are

(a) proteins

(b) carbohydrates

(c) lipids

(d) germs.

Answer and Explanation:

35. (a): Antibody is a protein produced by lymphocytes in response to entry into the body of a foreign substance (antigen) in order to render it harmless. It is typically a “Y”-shaped structure consisting of four polypeptide chains – two heavy chains and two light chains.

36. The term ‘active immunity’ means

(a) increasing rate of heart beat

(b) increasing quantity of blood

(c) resistance developed after disease

(d) resistance developed before disease.

Answer and Explanation:

36. (c): Active immunity is the immune response generated in an individual due to previous contact with disease or vaccination. In many cases, it is lifelong.

37. The blood group, with antibody-A and antibody- B is

(a) O

(b) B

(c) A

(d) AB.

Answer and Explanation:

37. (a): In human beings are present two antigens A and B produced by IA and ID alleles respectively. These antigens are always present on the surface of RBCs. Also are present two antibodies in the plasma anti A and anti B. The ABO blood groups are determined by the gene I having three alleles – IA, IB, 1°. Blood group O has both the antibodies – A and B but no antigens.

38. Which is the principal cation in the plasma of the blood?

(a) potassium

(b) magnesium

(c) calcium

(d) sodium.

Answer and Explanation:

38. (d): Blood consists of a watery fluid called plasma. Plasma is a faint yellow, slightly alkaline, viscous fluid. It consists of 90% water, 1% inorganic salts, 7% or 8% proteins and 1 % of other substances. The inorganic salts in plasma occur as ions. Sodium is the main cation of plasma and chloride, the main anion. Potassium, calcium and magnesium occur in small amount.

39. Rate of heart beat is determined by

(a) Purkinje fibres

(b) papillary muscles

(c) AV-node

(d) SA-node.

Answer and Explanation:

39. (d): The SA-node is located in the wall of the right auricle. It has a unique property of self excitation, which enables it to act as the pace maker of the heart. By determining the rate of discharge of the cardiac impulse the SA node determines the heart beat of the heart. It sets up cardiac impulses 72 times per minute.

40. In which point, pulmonary artery is different from pulmonary vein?

(a)

its lumen is broad

(b) its wall is thick

(c) it has valves

(d) it does not possess endothelium.

Answer:

(b) its wall is thick

41.

Difference between pulmonary artery and pulmonary vein is that, the pulmonary artery has

(a) no endothelium

(b) valves

(c) thicker walls

(d) oxygenated blood.

Answer and Explanation:

41. (b): An artery has thick and more elastic wall but its lumen is narrow as compared to vein. Pulmonary artery carries deoxygenated blood from the right ventricle to the lungs for oxygenation. Pulmonary vein carries oxygerated blood from the lungs io the left auricle.

42. What is correct for blood group O?

(a) no antigens but both a and b antibodies are i present

(b) A antigen and b antibody present

(c) antigen and antibody both absent

(d) A and B antigens and a, b, antibodies present,

Answer and Explanation:

42. (c): Refer answer 40.

43. Impulse of heart beat originates from

(a) S.A. node

(b) A.V. node

(c) vagus nerve

(d) cardiac nerve.

Answer and Explanation:

43. (a): Refer answer 37.

44. Bundle of His is a network of

(a) muscle fibres distributed throughout the heart walls

(b) muscle fibres found only in the ventricle wall

(c) nerve fibres distributed in ventricles

(d) nerve fibres found throughout the heart

Answer and Explanation:

44. (a): Refer answer 39

45. Short-lived immunity acquired from mother to foetus across placenta or through mother’s milk to the infant is categorised as

(a) active immunity

(b) passive immunity

(c) cellular immunity

(d) innate non-specific immunity

Answer and Explanation:

45. (b): Short-lived immunity acquired from mothers to foetus across placenta or through mother’s milk to the infant is categorised as passive immunity. Passive immunity, an acquired immunity, is resistance based on antibodies performed in another host. In this case, the foetus is not directly responsible for its body immunity but it becomes immunised by mother’s milk across placenta.

46. In the ABO system of blood groups, if both antigens are present but no antibody, the blood group of the individual would be

(a) B

(b) O

(c) AB

(d) A

Answer and Explanation:

46. (c): Human blood groups are special characteristics of blood in human and related primates due to presence of genetically controlled antigens and antibodies. ABO blood groups were the first to be discovered and are the most important in assuring safe blood transfusion.

This system reflects the presence or absence of A and B agglutinogens (antigen) which are carried on the surface of plasma membrane of red blood cells. The ABO blood groups are determined by the gene 1 having three alleles – 1A, 1B, 1°. In human being, there are present two antigens A and B produced by lA and 1H alleles respectively.

These antigens are always present on the surface of RBCs. Also are present two antibodies in the plasma-anti A and anti B. Blood group AB has both antigens A and B but no antibodies.

47. The cardiac pacemaker in a patient fails to function normally. The doctors find that an artificial pacemaker is to be grafted in him. It is likely that it will be grafted at the site of

(a) atrioventricular bundle

(b) Purkinje system

(c) sinuatrial node

(d) atrioventricular node.

Answer and Explanation:

47. (c): SA node is a specialised bundle of neurons located in the upper part of the right atrium of the heart. SA node is the natural cardiac pacemaker from which the heart beat originates. If this system is damaged, it may send non-coordinated impulses to the heart chambers resulting in symptoms like irregular heart rate, tiredness, dizziness and loss of consciousness. As the pacemaker cells create this rhythmical impulse therefore an artificial pacemaker is implanted at the site of SA node to mimic the actions of the node and conducting system and helps to regulate heart beat.

48. You are required to draw blood from a patient and to keep it in a test tube for analysis of blood corpuscles and plasma. You are also provided with the following four types of test tubes. Which of these will you not use for the purpose?

(a) test tube containing calcium bicarbonate

(b) chilled test tube

(c) test tube containing heparin

(d) test tube containing sodium oxalate.

Answer and Explanation:

48. (c): Clotting of collected blood can be prevented

• coating test tubes with silicon (which produce non wettable surface similar in its smoothness to endothelial lining of blood vessels).

• adding chelating agents (includes trisodium citrate, sodium oxalate and sodium EDTA) which remove calcium which is important for blood coagulation, and prevent blood clotting…

• adding Heparin, most powerful anticoagulant which acts indirectly by activating plasma antithrombin 111. Heparin is effective both in vivo and in vitro. Whereas the option a, b and d are effective in vitro.

Heparinized blood is not suitable for blood counts (as it alters the shape of RBCs and WBCs which affects blood testing), Fragility testing and complement fixation tests, Hence (c) is the correct answer.

49. AIDS is caused by HIV that principally infects

(a) all lymphocytes

(b) activator B cells

(c) cytotoxic T cells

(d) T4 lymphocytes.

Answer and Explanation:

49. (d): The AIDS retrovirus, called human immunodeficiency virus (HIV), mounts a direct attack on CD4 T cells because it recognizes the CD4 coreceptors associated with these cells.

HIV’s attack on CD4+ T cells cripples the immune system in at least three ways. First, HIV-infected cells die only 1 after releasing replicated viruses that infect other CD4; T cells, until the entire population of CD4+ T cell is, destroyed. Second, HIV causes infected CD4 T cells to 1 secrete a soluble suppressing factor that blocks other T cells from responding to the HIV antigen.

Finally, HIV may block transcription of MHC genes, hindering the recognition and destructure of infected CD4? T cells and thus protecting those cells from any remaining vestiges of the immune system. The combined effect of these responses to HIV infection is to wipe out the human immune defense.

50. Damage to thymus in a child may lead to

(a) a reduction in haemoglobin content of blood

(b) a reduction in stem cell production

(c) loss of antibody mediated immunity

(d) loss of cell mediated immunity.

Answer and Explanation:

50. (d): The thymus is the major gland of our immune system. The thymus is responsible for many immune system functions including the production of T- lymphocytes, a type of white blood cell responsible for cell mediated immunity. Cell mediated immunity is a type of immunity in which specialized cells carry out defensive activities. They protect the body against pathogens including the protists and fungi which have entered the host’s cells. T-cells and B-cells arc the type of lymphocytes that develop from bone marrow cells.

Those lymphocytes that migrate to the thymus and differentiate are called T-cells and those cells that continue to be in the bone marrow for differentiation are known as B-cells. T-cells are responsible for cell mediated immunity, however, B-cells produce antibodies and take part in antibody mediated immunity.

51. Which one of the following has an open circulatory system?

(a) octopus

(b) Pheretima

(c) Periplaneta

(d) Hirudinaria

Answer and Explanation:

51. (c): Periplaneta has open circulatory system i.e. the blood does not flow in blood vessels but flows in a haemocoel (body cavity). The circulatory systems of all vertebrates, as well as of annelids (for example, earthworms) and cephalopods (squid and octopus) are closed, in which the blood never leaves the system of blood vessels consisting of arteries, capillaries and vejns.

52. Antibodies in our body are complex

(a) glycoproteins

(b) lipoproteins

(c) steroids

(d) prostaglandins

Answer and Explanation:

52. (a): Antibody are members of a class of proteins known as immunoglobulins. Immunoglobulins are glycoproteins in the immunoglobulin superfamily. The terms antibody and immunoglobulin are often used interchangeably. They are found in the blood and tissue fluids, as well as many secretions. In structure, they are globulins (in the y-region of protein electrophoresis).

They are synthesized and secreted by plasma cells that are derived from the B cells of the immune system. B cells are activated upon binding to their specific antigen and differentiate into plasma cells. In some cases, the interaction of the B cell with a T helper cell is also necessary. They are used by the immune system to identify and neutralize foreign objects like bacteria and viruses. Each antibody recognizes a specific antigen unique to its target. Production of antibodies is referred to as the humoral immune system.

53. HIV that causes AIDS first starts destroying

(a) helper T-lymphocytes

(b) B-lymphocytes

(c) leucocytes

(d) thrombocytes.

Answer and Explanation:

53. (a): AIDS, also known as acquired immunodeficiency syndrome, is a sexually transmitted disease of the human immune system that is caused by infection with HIV. It is characterized cytologically especially by reduction in the numbers of CD4-bearing helper T cells to 20 percent or less of normal.

HIV (Human Immunodeficiency Virus) is a retrovirus that infects cells of the human immune system. HIV virus can be found in body fluids (blood, semen, and breast milk).

54. Lysozyme that is present in perspiration, saliva and tears, destroys

(a) certain types of bacteria

(b) all viruses

(c) most virus-infected cells

(d) certain fungi

Answer and Explanation:

54. (a): Lysozyme is an antibacterial enzyme with natural antibiotic properties. Normally excreted in the tears, nasal mucus, milk, and saliva in most animals, lysozyme is part of the body’s first natural defence against bacteria and viruses. Lysozyme is enzymes that degrade the polysaccharide protective coating on the surface of many bacteria and viruses (glycoprotein covering) to allow other enzymes and antibodies to find their appropriate attachment sight. Most of the bacteria affected by lysozyme are not pathogenic.

Lysozyme serves as a non-specific innate opsonin by binding to the bacterial surface, reducing the negative charge and facilitating phagocytosis of the bacterium before opsonins from the acquired immune system arrive at the scene. In other words, lysozyme makes it easier for phagocytic white blood cells to engulf bacteria.

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