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The Vault
RowQ
The Vault
CBSE Class 11 Biology · 10 questions · 24 marks
Every cell in the body depends on a moving fluid to bring it food and oxygen and to carry away waste, and this chapter follows that fluid through two connected loops: blood and lymph. It builds from the composition of blood plasma and cells up through the pumping heart, its own electrical wiring, and the double circulation that keeps oxygenated and deoxygenated blood from mixing, ending with the disorders that arise when the pressure in this system runs too high or too low.
The blood cells that lack a nucleus in mature mammals and are packed with haemoglobin are the:
Answer
Erythrocytes is correct — mature mammalian red blood cells extrude their nucleus during development, leaving the cell biconcave and filled with haemoglobin to maximise its oxygen-carrying capacity, unlike leucocytes, which remain nucleated.
The natural pacemaker of the human heart, which initiates each heartbeat, is the:
Answer
Sinoatrial node is correct — located in the wall of the right atrium, it generates rhythmic electrical impulses faster than any other part of the conducting system, so it sets the pace for the whole heart and is therefore called the pacemaker.
In an ECG trace, the QRS complex specifically represents:
Answer
Ventricular depolarisation is correct — the QRS complex is the sharp spike recorded as the electrical wave spreads through the ventricular muscle just before ventricular systole, while the earlier P wave marks atrial depolarisation and the later T wave marks ventricular repolarisation.
The plasma protein directly responsible for forming the fibre meshwork of a blood clot is:
Answer
Fibrinogen is correct — thrombin, generated during the clotting cascade, converts soluble fibrinogen in the plasma into insoluble fibrin threads that weave together to trap blood cells and form the clot.
Assertion (A): An Rh-negative mother's first Rh-positive child is usually born without complications, but a second Rh-positive child can be at serious risk. Reason (R): Exposure to foetal Rh antigen during the first delivery causes the mother to produce anti-Rh antibodies, which can cross the placenta in a later pregnancy and attack the next Rh-positive foetus's red blood cells.
Answer
Both A and R are true and R is the correct explanation of A — significant mixing of foetal and maternal blood typically happens only at delivery, so antibody formation begins afterward; these antibodies then persist and can cross into a subsequent pregnancy, causing erythroblastosis foetalis in an Rh-positive foetus.
Distinguish between pulmonary circulation and systemic circulation in the human double circulatory system.
Answer
Pulmonary circulation carries deoxygenated blood from the right ventricle through the pulmonary artery to the lungs, where it is oxygenated, and returns it via the pulmonary veins to the left atrium; this is a short, low-pressure loop dedicated purely to gas exchange. Systemic circulation carries oxygenated blood from the left ventricle through the aorta to all body tissues, where oxygen and nutrients are delivered and carbon dioxide and wastes are picked up, and returns deoxygenated blood via the venae cavae to the right atrium; this is a much longer, higher-pressure loop supplying the entire body. Because these two loops are kept separate by the four-chambered heart, oxygenated and deoxygenated blood do not mix.
Describe the sequence of events in the cardiac cycle and explain what produces the characteristic heart sounds.
Answer
The cardiac cycle begins with joint diastole, in which all four chambers are relaxed and blood flows passively from the veins into the atria and then into the ventricles through the open atrioventricular valves. This is followed by atrial systole, a brief contraction of the atria that pushes the remaining blood into the ventricles, completing ventricular filling. Ventricular systole then follows: the ventricles contract, pressure inside them rises sharply, the atrioventricular valves snap shut to prevent backflow into the atria (producing the first heart sound, 'lub'), and the semilunar valves at the base of the aorta and pulmonary artery open, ejecting blood into these great vessels. As ventricular pressure falls after ejection, the semilunar valves close to prevent blood flowing back into the ventricles, producing the second heart sound ('dub'), and the cycle returns to joint diastole. The whole cycle takes about 0.8 seconds at a resting heart rate of 72 beats per minute.
Describe the structure of the human heart and trace the path of blood through its chambers during one complete cardiac cycle.
Answer
The human heart is a four-chambered muscular organ about the size of a fist, enclosed within a double-layered protective sac called the pericardium and located in the thoracic cavity between the lungs. It has two smaller upper chambers, the right and left atria, and two larger, thicker-walled lower chambers, the right and left ventricles, with the interventricular septum keeping the right and left sides permanently separate. Deoxygenated blood returning from the body through the superior and inferior venae cavae enters the right atrium, which contracts and pushes it through the tricuspid valve into the right ventricle; the right ventricle then contracts, forcing this blood past the pulmonary semilunar valve into the pulmonary artery, which carries it to the lungs for oxygenation. Freshly oxygenated blood returns from the lungs through the pulmonary veins into the left atrium, which contracts and pushes it through the bicuspid (mitral) valve into the left ventricle, the most muscular chamber because it must generate enough pressure to pump blood to the entire body. The left ventricle then contracts forcefully, pushing blood past the aortic semilunar valve into the aorta, from where it is distributed throughout the systemic circulation. At every stage, the atrioventricular and semilunar valves open and close in coordination to ensure blood flows in one direction only, and this entire sequence of atrial and ventricular contraction and relaxation, repeating roughly seventy-two times a minute, constitutes one cardiac cycle.
Explain the process of blood clotting, and describe how the ABO and Rh blood grouping systems determine transfusion compatibility.
Answer
Blood clotting is a protective cascade that seals a wound and prevents excessive blood loss. When a blood vessel is injured, platelets at the site clump together and, along with the damaged tissue, release a substance called thromboplastin. In the presence of calcium ions, thromboplastin converts the inactive plasma protein prothrombin into its active form, thrombin. Thrombin then acts as an enzyme that converts soluble fibrinogen, another plasma protein, into insoluble threads of fibrin; these threads form a mesh that traps blood cells and platelets, forming a solid clot that plugs the wound. The ABO blood grouping system is based on the presence or absence of two antigens, A and B, on the surface of red blood cells: a person with only antigen A is blood group A, only antigen B is group B, both antigens is group AB, and neither is group O; plasma correspondingly contains antibodies against whichever antigen is absent from the person's own cells, so mixing incompatible blood causes the antibodies to agglutinate (clump) the foreign red cells, which is dangerous. Group O individuals, lacking both antigens, are called universal donors, while group AB individuals, lacking both antibodies, are called universal recipients under simplified rules. The Rh system adds a separate antigen, the Rh factor; individuals with this antigen are Rh-positive and those without are Rh-negative, and an Rh-negative person given Rh-positive blood will develop anti-Rh antibodies, making a subsequent transfusion of Rh-positive blood potentially dangerous, so both ABO and Rh compatibility must be checked before any transfusion.
A 55-year-old man reports recurring chest pain during exertion that eases with rest. His blood pressure is recorded at 158/98 mm Hg on three separate visits. Investigation reveals narrowing of one of the coronary arteries supplying his heart muscle. (a) Identify the condition causing his exertional chest pain and explain why it eases with rest. (b) What term describes his elevated blood pressure reading, and what two numbers make up a blood pressure reading? (c) Why does narrowing of a coronary artery specifically threaten heart muscle rather than some other tissue? (d) Suggest one lifestyle change that could help reduce his risk of a more serious cardiac event.
Answer
(a) His symptom is angina, chest pain that arises when the heart muscle temporarily receives insufficient oxygen relative to its demand, typically during physical exertion when the heart works harder; resting reduces the heart's oxygen demand back to a level the narrowed artery can still supply, so the pain eases. (b) His reading describes hypertension, since it exceeds the normal threshold of about 140/90 mm Hg. A blood pressure reading consists of the systolic pressure (the higher number, pressure during ventricular contraction) over the diastolic pressure (the lower number, pressure during ventricular relaxation). (c) The coronary arteries are the specific vessels that branch off the aorta to supply oxygenated blood directly to the heart muscle itself; narrowing of these arteries starves the heart muscle cells of oxygen even while the rest of the body may be adequately supplied, and heart muscle has very limited capacity to work without a continuous oxygen supply. (d) Adopting a lower-fat, lower-salt diet together with regular moderate exercise and avoiding tobacco would help reduce both his blood pressure and the progression of coronary artery narrowing.
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