Consider these statements about the biochemical cascade of blood clotting:
(i) Fibrins are formed by the conversion of inactive fibrinogen in plasma by the enzyme thrombokinase. (ii) Thrombin is formed from inactive prothrombin by the enzyme complex thrombokinase. (iii) The thrombokinase enzyme complex is formed by a series of linked enzymic reactions (cascade process) involving several inactive plasma factors. (iv) Calcium ions play a very important role in blood clotting.
Explanation: Statements (ii), (iii), and (iv) are correct. Statement (i) is incorrect because thrombin converts fibrinogen into fibrin, whereas thrombokinase converts prothrombin into thrombin.
Question 82 of 100
📘 CLASS XI
Read the following statements regarding heart chambers and their partitions:
(i) The human heart has four chambers: two relatively small upper atria and two larger lower ventricles. (ii) The walls of the ventricles are much thicker than those of the atria. (iii) A thin, muscular wall called the inter-atrial septum separates the right and left ventricles. (iv) A thick-walled inter-ventricular septum separates the left and the right ventricles.
Explanation: Statements (i), (ii), and (iv) are correct. Statement (iii) is incorrect because the inter-atrial septum separates the right and left atria, while the ventricles are separated by the inter-ventricular septum.
Question 83 of 100
📘 CLASS XI
Examine these statements about the valves guarding human cardiac openings:
(i) The tricuspid valve, consisting of three muscular flaps, guards the opening between the right atrium and the right ventricle. (ii) The bicuspid (mitral) valve guards the opening between the left atrium and left ventricle. (iii) The openings of the right ventricle into the aorta and the left ventricle into the pulmonary artery are guarded by semilunar valves. (iv) Heart valves strictly enforce unidirectional blood flow and prevent backflow.
Explanation: Statements (i), (ii), and (iv) are correct. Statement (iii) is incorrect because the right ventricle opens into the pulmonary artery and the left ventricle opens into the aorta. The statement reverses these vessels.
Question 84 of 100
📘 CLASS XI
Study the statements regarding the endocrine and neural regulation of cardiac activity:
(i) The autonomic nervous system regulates heart activity via a specialized neural center located in the pons. (ii) Sympathetic neural signals can increase the rate of heartbeat, the strength of ventricular contraction, and thereby the cardiac output. (iii) Parasympathetic neural signals decrease the rate of heartbeat, the speed of action potential conduction, and the cardiac output. (iv) Adrenal medullary hormones can also act to increase the cardiac output.
Explanation: Statements (ii), (iii), and (iv) are correct. Statement (i) is incorrect because the cardiac regulatory center is located in the medulla oblongata, not the pons.
Question 85 of 100
📘 CLASS XI
Read these statements regarding coronary artery disease (CAD) and angina pectoris:
(i) Angina pectoris refers to acute chest pain that appears when insufficient oxygen is reaching the heart muscle. (ii) Angina is a chronic inflammatory condition restricted exclusively to elderly males. (iii) Coronary Artery Disease (CAD), often referred to as atherosclerosis, affects the vessels that supply blood to the heart muscle. (iv) CAD is caused by deposits of calcium, fat, cholesterol, and fibrous tissues, which make the arterial lumen narrower.
Explanation: Statements (i), (iii), and (iv) are correct. Statement (ii) is incorrect because angina can occur in both men and women, although it is more common among middle-aged and elderly individuals.
Question 86 of 100
📘 CLASS XI
Consider these statements regarding the clinical parameters of Stroke Volume and Cardiac Output:
(i) Stroke volume is the volume of blood pumped out by each ventricle during a single cardiac cycle, which is approximately 70 mL. (ii) Cardiac output is defined as the volume of blood pumped out by both ventricles combined per minute. (iii) Cardiac output averages about 5000 mL (5 litres) in a healthy individual. (iv) The body has the ability to alter cardiac output by modifying either the stroke volume, the heart rate, or both.
Explanation: Statements (i), (iii), and (iv) are correct. Statement (ii) is incorrect because cardiac output refers to the volume of blood pumped by each ventricle per minute, not both ventricles combined.
Question 87 of 100
📘 CLASS XI
Read the statements below regarding the physical mechanisms producing heart sounds:
(i) During each cardiac cycle, two prominent heart sounds can be easily heard through a stethoscope. (ii) The first heart sound, 'lub', is associated with the opening of the tricuspid and bicuspid valves. (iii) The second heart sound, 'dub', is associated with the closure of the semilunar valves. (iv) Heart sounds are of high clinical diagnostic significance.
Explanation: Statements (i), (iii), and (iv) are correct. Statement (ii) is incorrect because the first heart sound (lub) is produced by the closure, not the opening, of the tricuspid and bicuspid valves.
Question 88 of 100
📘 CLASS XI
Examine these statements about the prevention and pathology of Erythroblastosis Foetalis:
(i) Erythroblastosis foetalis occurs due to Rh incompatibility between an Rh-negative mother and an Rh-positive foetus. (ii) During the first pregnancy, Rh antigens of the foetus do not expose maternal blood because the two bloods are separated by the placenta. (iii) During subsequent pregnancies, maternal Rh antibodies leak into the foetal blood, causing severe anemia and jaundice. (iv) The condition can be avoided by administering anti-Rh antibodies to the newborn baby immediately after birth.
Explanation: Statements (i), (ii), and (iii) are correct. Statement (iv) is incorrect because anti-Rh antibodies are administered to the Rh-negative mother immediately after the delivery of the first Rh-positive child.
Question 89 of 100
📘 CLASS XI
Study the properties of the Sino-Atrial Node (SAN) in the cardiac conduction system:
(i) The sino-atrial node (SAN) is a specialized patch of cardiac musculature located in the right upper corner of the right atrium. (ii) SAN has the ability to generate action potentials without any external stimuli (making it autoexcitable). (iii) The SAN generates 70–75 action potentials per minute, which is the highest rate in the nodal system. (iv) The SAN is called the pacemaker because it initiates and maintains the rhythmic contractile activity of the heart.
Explanation: All four statements are correct. The sino-atrial node is autoexcitable, generates action potentials at the highest rate (70–75 per minute), and acts as the natural pacemaker of the heart.
Question 90 of 100
📘 CLASS XI
Read the statements below regarding human portal and specialized circulations:
(i) A unique vascular connection exists between the digestive tract and the liver, called the hepatic portal system. (ii) The hepatic portal vein carries blood from the liver directly to the systemic vena cava. (iii) The blood from the digestive tract passes through the liver before entering the general systemic circulation. (iv) A special coronary system of blood vessels exists solely to circulate blood to and from the cardiac musculature.
Explanation: Statements (i), (iii), and (iv) are correct. Statement (ii) is incorrect because the hepatic portal vein carries blood from the digestive tract to the liver, not from the liver to the vena cava.
