Consider the following statements regarding the biochemistry of blood coagulation:
(i) Inactive prothrombin is converted to active thrombin by the enzyme complex thrombokinase. (ii) Soluble fibrinogen is converted into insoluble fibrin threads by the enzyme thrombin. (iii) Thrombokinase is a single protein factor synthesized directly by the liver in an active state. (iv) Calcium ions are not required for the final conversion of fibrinogen to fibrin.
Explanation: Statements (i) and (ii) are correct. Statement (iii) is incorrect because thrombokinase is an enzyme complex generated through a clotting cascade, not a single liver protein. Statement (iv) is incorrect because calcium ions are essential for blood coagulation.
Question 32 of 100
📘 CLASS XI
Read the statements regarding the components and functions of lymph (tissue fluid):
(i) Lymph contains larger proteins and all formed elements of blood. (ii) Lymph has the same mineral distribution as that found in plasma. (iii) Lymph is a colour-rich fluid because it contains specialized lymphocytes. (iv) Fats are absorbed through lymph in the lacteals present in the intestinal villi.
Explanation: Statements (ii) and (iv) are correct. Statement (i) is incorrect because larger plasma proteins and most formed elements remain in the blood vessels. Statement (iii) is incorrect because lymph is a colourless fluid containing lymphocytes.
Question 33 of 100
📘 CLASS XI
Study these statements about vertebrate circulatory pathways:
(i) Fishes possess a 2-chambered heart with single circulation. (ii) Amphibians have incomplete double circulation due to a single ventricle where oxygenated and deoxygenated blood mix. (iii) Reptiles, including crocodiles, show incomplete double circulation. (iv) Birds and mammals have 4-chambered hearts with complete double circulation.
Explanation: Statements (i), (ii), and (iv) are correct. Statement (iii) is incorrect because crocodiles are an exception among reptiles and possess a four-chambered heart with complete double circulation.
Question 34 of 100
📘 CLASS XI
Examine the following statements regarding human heart anatomy and septa:
(i) The inter-atrial septum is a thin, muscular wall separating the right and left atria. (ii) The inter-ventricular septum is a thick-walled structure separating the left and right ventricles. (iii) The atrium and ventricle of the same side are separated by a thick, highly muscular septum. (iv) The muscular walls of the ventricles are much thinner than those of the atria.
Explanation: Statements (i) and (ii) are correct. Statement (iii) is incorrect because the atrium and ventricle are separated by a thick fibrous atrio-ventricular septum, not a muscular septum. Statement (iv) is incorrect because ventricular walls are much thicker than atrial walls.
Question 35 of 100
📘 CLASS XI
Read these statements regarding heart valves and their roles:
(i) The tricuspid valve guards the opening between the right atrium and the right ventricle. (ii) The mitral valve is a bicuspid valve guarding the opening between the left atrium and left ventricle. (iii) The openings of the right and left ventricles into the pulmonary artery and aorta are provided with semilunar valves. (iv) Heart valves allow blood to flow in both directions to maximize pumping efficiency.
Explanation: Statements (i), (ii), and (iii) are correct. Statement (iv) is incorrect because heart valves ensure one-way blood flow and prevent backflow.
Question 36 of 100
📘 CLASS XI
Consider these statements regarding the structural parts of the cardiac nodal tissue:
(i) The sino-atrial node (SAN) is located in the upper right corner of the right atrium. (ii) The atrio-ventricular node (AVN) is situated in the lower left corner of the right atrium close to the AV septum. (iii) The AV bundle continues from the AVN and immediately divides into right and left bundles at the top of the inter-ventricular septum. (iv) Purkinje fibres are minute fibres arising from bundle branches throughout the atrial musculature.
Explanation: Statements (i), (ii), and (iii) are correct. Statement (iv) is incorrect because Purkinje fibres are distributed throughout the ventricular musculature, not the atrial musculature.
Question 37 of 100
📘 CLASS XI
Read the following statements regarding heart muscle and its electrical characteristics:
(i) The entire heart is made of smooth muscles. (ii) The nodal tissue can generate action potentials without any external stimuli, making it autoexcitable. (iii) The rate of action potential generation is completely uniform throughout all parts of the nodal system. (iv) The SAN generates the maximum number of action potentials, about 70–75 min-1.
Explanation: Statements (ii) and (iv) are correct. Statement (i) is incorrect because the heart is composed of cardiac muscle. Statement (iii) is incorrect because different parts of the nodal system generate action potentials at different intrinsic rates, with the SAN having the highest rate.
Question 38 of 100
📘 CLASS XI
Analyze these statements regarding the Joint Diastole phase of the cardiac cycle:
(i) All four chambers of the heart are in a relaxed state. (ii) Tricuspid and bicuspid valves are closed to prevent backflow of blood. (iii) Semilunar valves of the aorta and pulmonary artery are closed. (iv) Blood from pulmonary veins and vena cava flows into the left and right ventricles respectively.
Explanation: Statements (i), (iii), and (iv) are correct. Statement (ii) is incorrect because during joint diastole the atrio-ventricular (tricuspid and bicuspid) valves are open, allowing blood to flow from the atria into the ventricles.
Question 39 of 100
📘 CLASS XI
Read the statements below regarding the events of Atrial Systole:
(i) Atrial systole is initiated by an action potential generated by the AVN. (ii) It involves the simultaneous contraction of both atria. (iii) It increases the flow of blood into the ventricles by about 30 percent. (iv) During atrial systole, semilunar valves are forced open.
Explanation: Statements (ii) and (iii) are correct. Statement (i) is incorrect because atrial systole is initiated by the sino-atrial node (SAN), not the AVN. Statement (iv) is incorrect because the semilunar valves remain closed during atrial systole.
Question 40 of 100
📘 CLASS XI
Study the statements regarding Ventricular Systole and associated valve actions:
(i) Ventricular contraction is triggered by action potentials conducted via the AVN, AV bundle, and bundle of His. (ii) Ventricular systole increases ventricular pressure, causing the opening of the tricuspid and bicuspid valves. (iii) Closure of atrioventricular (AV) valves prevents blood backflow and is associated with the first heart sound, 'lub'. (iv) As ventricular pressure increases further, semilunar valves are forced open, allowing blood into the arteries.
Explanation: Statements (i), (iii), and (iv) are correct. Statement (ii) is incorrect because increased ventricular pressure closes the tricuspid and bicuspid valves to prevent backflow into the atria.
