NCERT Exemplar MCQs

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(c) Phagocytes have the ability to phagocytose or kill foreign cells and particles like pathogens by ingesting them. Many blood cells have this function, including monocytes, neutrophils, and macrophages. Basophils do not have phagocytic activity.

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(c) Dengue is a type of fever caused by the dengue virus and propagated by mosquitoes. A significant decrease in the number of platelets is observed in this disease.

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(a) During a cardiac cycle, each ventricle pumps out approximately \(70 \mathrm{~mL}\) of blood, thus, both the ventricles pump out the same volume of blood in each cardiac cycle.

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(b) Cardiac activity could be moderated by the autonomous neural system. The action of sympathetic nerve fibres increases the heart rate and the stroke volume, while that of the parasympathetic nerve fibres decrease these. Thus, the correct answer is “The sympathetic system stimulates the heart rate and stroke volume.’

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(b) Calcium ions and platelets are essential factors for the clotting of blood. During some injuries, the platelets release inactivated platelet factors that are involved in the activation of other factors involved in the formation of clots in the blood. Calcium ions in the blood catalyze the activation of many factors involved in clot formation like factor VIII, factor IX, factor V, and factor XIII.

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(b) An electrocardiogram or an ECGuses an instrument to record the electrical activities of the heart. It records the electrical impulses, more specifically the change in the electrical impulses of the heart, and plots it on a graph. The readings of an individual’s ECG are compared with a standard ECG to evaluate the working of the heart and checking it for any abnormalities or diseases. Different waves in ECG represent different events in the cardiac cycle but none of them depicts the repolarization of the atria.

A normal ECG represents P-wave atrial depolarisation QRS complex-ventricular depolarisation T-wave ventricular repolarisation. Therefore, atrial repolarisation is not represented in an electrocardiogram (ECG).

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(a) RBCs (Red Blood Corpuscles) in humans lack nucleus. The absence of nucleus in the cell reduces the \(\mathrm{O}_{2}\) consumption by the cell in various cellular activities. Therefore, the cell is able to transport the maximum amount of \(\mathrm{O}_{2}\) to other cells of the body.

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(a) Antibodies are proteins released by \(B\)-cells that target and work against specific antigens. These \(B\)-cells are a type of lymphocytes and hence are also referred to as \(B\)-lymphocytes. Thus, the correct answer is ‘ \(B\)-Lymphocytes.’

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(c) SA Node It is situated in the walls of the right auricle near the opening of the superior vena cava. In the myogenic heart, the contraction is initiated by the SA node.

AV Node The wave of contraction reaches the AV node which is stimulated to emit an impulse of contraction spreading to the ventricular muscle via the atrioventricular bundle and then to the Purkinje fibres stimulating heartbeat.

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(a) The blood cells are of three major types they are erythrocytes(RBC), leucocytes(WBC), and platelets. Two main categories of WBCs are granulocytes and agranulocytes. Neutrophils, eosinophils, and basophils are different types of granulocytes, while lymphocytes and monocytes are the agranulocytes. When basophils are encountered with allergin they release histamine which causes increased blood flow to damaged tissues, resulting in swelling and inflammation. Hence blood cells involved in inflammatory reactions are Basophils. So, the correct answer is ‘Basophils’.

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(b) The closing of different valves in the heart produces different characteristic sound commonly known as the lubb-dubb sounds. The lubb sound is the first sound of the heart. The dubb sound is the second sound of the heart that is produced by the closing of the semilunar valves in the heart. Thus, the correct answer is ‘Semilunar valves.’

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(b) QRS Complex QRS wave (complex) begins after a fraction of second after the P wave. It begins as a small downward deflection (Q) and continues as a large upright (R) and triangular wave, ending as downward wave (S) at its base.

This represents ventricular depolarisation (ventricular contraction). Thus, the other options are wrong.

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(c) ABO blood grouping in human is based on the presence or absence of two surface antigens on the RBCs namely A and B. Similarly, the plasma of different individuals contain two natural antibodies. This distribution of antigens and antibodies in the four groups of blood \(A, B, A B\) and \(O\) are as follows
\(
\begin{aligned}
&\text { Blood Groups and Donors Compatibility }\\
&\begin{array}{c|c|c|c}
\hline \begin{array}{c}
\text { Blood } \\
\text { Group }
\end{array} & \begin{array}{c}
\text { Antigens on } \\
\text { RBCs }
\end{array} & \begin{array}{c}
\text { Antibodies } \\
\text { in Plasma }
\end{array} & \begin{array}{c}
\text { Donor’s } \\
\text { Group }
\end{array} \\
\hline \text { A } & \text { A } & \text { anti-B } & \text { A, O } \\
\text { B } & \text { B } & \text { anti-A } & \text { B, O } \\
\text { AB } & \text { A, B } & \text { nil } & \text { AB, A, B, O } \\
\text { O } & \text { nil } & \text { anti-A, B } & O \\
\hline
\end{array}
\end{aligned}
\)
Thus, the blood group in universal donor 4 blood group \(A B\) is the universal recipient and the other options are correct.

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(b) Cardiac output \(=\) Heart beats \(/\) min \(\times\) stroke volume
\(
=72 \text { beats } / \min \times 50 \mathrm{~mL} / \text { beat }=3600 \mathrm{~mL} / \mathrm{min} \text {. }
\)

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(b)

A. Lymphatic system: It permeates the entire body. It drains excess tissue fluid from the extracellular spaces back into the blood.
B. Pulmonary vein: Blood takes up oxygen and becomes oxygenated. Four great veins, called pulmonary veins, two from each lung, return the oxygenated blood from the alveolar capillaries to the left auricle.

C. Thrombocytes: They are found in vertebrates other than mammals. The spindle cells aid in the clotting of blood like the platelets of mammals.

D. Lymphocytes: They secrete antibodies to destroy microbes and their toxins, reject grafts, and kill tumour cells.

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(d) The superior vena cava pours venous blood into the right atria and the left atria receives blood from the lungs. This then flows into the ventricles. The contraction of muscles of atria arises from SA nodes and passes to the AV node and then to the Purkinje fibres.