Chapter 15: Body Fluids and Circulation Long Questions | biology Class 11 CBSE

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Chapter 15: Body Fluids and Circulation Long Questions | biology Class 11 CBSE | ByteNotes.in

Long Answer

Hard difficulty • Structured explanation

Hard

Question 1

Long Form

Compare and contrast the composition and functions of the different types of leucocytes, and explain how they collectively defend the body.

Leucocytes (WBCs) are nucleated, colourless cells averaging 6,000–8,000 per mm3, divided into granulocytes (with granular cytoplasm) and agranulocytes (non-granular).
Neutrophils (60–65%) are the most abundant granulocytes; they are phagocytic, engulfing and destroying bacteria and foreign organisms that enter the body.
Eosinophils (2–3%) resist infections and are associated with allergic reactions; basophils (0.5–1%) secrete histamine, serotonin, and heparin, mediating inflammatory responses.
Monocytes (6–8%) are phagocytic agranulocytes that differentiate into macrophages in tissues, providing a second line of defence against pathogens.
Lymphocytes (20–25%) are agranulocytes of two major types — B lymphocytes produce antibodies (humoral immunity) and T lymphocytes carry out cell-mediated immunity.
Together, these cells provide layered protection: immediate phagocytosis by neutrophils and monocytes, histamine-based inflammation by basophils, anti-parasitic action by eosinophils, and antigen-specific immunity by lymphocytes.

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Long Answer

Hard difficulty • Structured explanation

Hard

Question 2

Long Form

Trace the evolutionary changes in the pattern of heart structure and circulation across vertebrates, from fishes to mammals.

All vertebrates possess a muscular, chambered heart, but its complexity increases with evolutionary advancement in adaptation to terrestrial life.
Fishes have a 2-chambered heart (one atrium, one ventricle) with single circulation — deoxygenated blood is pumped to the gills for oxygenation and then to the body.
Amphibians and most reptiles (except crocodiles) have a 3-chambered heart (two atria, one ventricle) with incomplete double circulation — though oxygenated and deoxygenated blood both reach the ventricle, they get mixed, reducing oxygen delivery efficiency.
Crocodiles, birds, and mammals have a 4-chambered heart (two atria, two ventricles), enabling complete double circulation with no mixing of oxygenated and deoxygenated blood.
In complete double circulation, pulmonary circulation oxygenates blood and delivers it to the left side, while systemic circulation distributes oxygenated blood to all tissues from the left side.
The evolutionary progression from single to complete double circulation reflects increasing metabolic demand and thermoregulatory requirements in higher vertebrates.

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Long Answer

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Question 3

Long Form

Describe the complete sequence of events in a cardiac cycle, including the role of valves and nodal tissue at each stage.

The cardiac cycle begins with joint diastole — all four chambers relax, tricuspid and bicuspid valves are open, and blood flows from pulmonary veins and vena cava into the ventricles through the atria; semilunar valves remain closed.
The SAN generates an action potential, triggering simultaneous atrial systole — both atria contract, increasing blood flow into the ventricles by about 30%; the AVN receives the impulse.
The impulse travels via the AV bundle (Bundle of His) and Purkinje fibres to all ventricular muscle cells, triggering ventricular systole — ventricles contract powerfully while atria relax (atrial diastole).
Rising ventricular pressure causes closure of the AV valves (producing 'lub' sound), preventing backflow; further pressure rise forces open the semilunar valves, ejecting blood into the pulmonary artery and aorta.
Ventricles then relax (ventricular diastole), pressure falls, semilunar valves close (producing 'dub' sound) preventing backflow; AV valves open as atrial pressure exceeds ventricular pressure.
Blood again flows freely into the ventricles from the atria (joint diastole), the SAN fires again, and the cycle of 0.8 seconds repeats approximately 72 times per minute.

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Hard

Question 4

Long Form

Analyse the mechanism of blood coagulation, naming all key molecules involved and explaining the cascade process.

Blood coagulation is initiated when an injury or trauma stimulates platelets to release clotting factors; tissues at the injury site also release factors that trigger the cascade.
These factors activate a series of linked enzymic reactions (cascade process) involving multiple plasma proteins present in inactive form, ultimately producing the enzyme complex thrombokinase.
Thrombokinase catalyses the conversion of inactive prothrombin (present in plasma) into active thrombin — this is the critical regulatory step of the cascade.
Thrombin then acts on soluble fibrinogen (a plasma protein) and converts it into insoluble fibrin threads that form a mesh at the wound site.
The fibrin network traps dead and damaged formed elements of blood — RBCs, platelets, WBCs — forming a dark reddish-brown clot (coagulum) that physically seals the wound.
Calcium ions (Ca2+) play a vital role throughout the cascade, acting as cofactors for multiple enzymic reactions; without calcium, efficient clotting cannot occur.

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Long Answer

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Medium

Question 5

Long Form

Explain the ABO and Rh blood grouping systems and discuss why accurate blood grouping is critical before transfusion.

ABO grouping is based on the presence or absence of surface antigens A and B on RBCs and corresponding natural antibodies (anti-A, anti-B) in plasma — giving four blood groups: A, B, AB, and O.
Group O has no antigens (universal donor) and both antibodies; Group AB has both antigens but no antibodies (universal recipient); Groups A and B carry one antigen each with its opposing antibody.
Rh grouping is based on the presence (Rh+ve, ~80% of humans) or absence (Rh-ve) of the Rh antigen on RBC surfaces; Rh+ve and Rh-ve groups must also be matched for transfusion.
An Rh-ve recipient who receives Rh+ve blood forms Rh antibodies; a subsequent transfusion of Rh+ve blood triggers a severe haemolytic reaction.
During transfusion, if donor antigens encounter recipient antibodies, agglutination (clumping and destruction of RBCs) occurs, which can be life-threatening and may cause organ failure.
Therefore, both ABO and Rh matching are mandatory before any blood transfusion to prevent immune-mediated haemolysis and to ensure patient safety.

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Long Answer

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Medium

Question 6

Long Form

Describe the structure of the human heart, including its chambers, septa, valves, and the nodal tissue system.

The human heart is a mesodermally derived, fist-sized muscular organ located in the thoracic cavity between the lungs, slightly tilted to the left, and protected by the double-walled pericardium enclosing pericardial fluid.
It has four chambers: two smaller upper atria (separated by the inter-atrial septum) and two larger lower ventricles (separated by the thick inter-ventricular septum); atria and ventricles on the same side are separated by the atrio-ventricular septum.
The tricuspid valve (three cusps) guards the right atrio-ventricular opening; the bicuspid or mitral valve (two cusps) guards the left; semilunar valves guard the exits to the pulmonary artery and aorta, ensuring unidirectional blood flow.
Specialised nodal tissue is distributed in the heart: the SAN (right upper corner of right atrium) generates 70–75 action potentials/min and is the pacemaker; the AVN (lower left corner of right atrium) relays impulses to the ventricles.
The AV bundle (Bundle of His) conducts impulses from the AVN through the atrio-ventricular septa, splits into right and left bundle branches, and terminates as Purkinje fibres that spread excitation throughout the ventricular musculature.
All of these structural features ensure coordinated, efficient pumping of approximately 5 litres of blood per minute through both pulmonary and systemic circulatory pathways.

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Long Answer

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Medium

Question 7

Long Form

Compare the composition and properties of blood and lymph, and explain the route by which lymph is formed and returned to blood.

Blood consists of plasma (55%) and formed elements (45% — RBCs, WBCs, platelets), while lymph is a colourless fluid derived from tissue fluid and contains specialised lymphocytes but lacks RBCs and most plasma proteins.
Both blood and lymph share the same mineral distribution; however, lymph contains far fewer proteins and no formed elements such as RBCs and platelets, making it less viscous.
Lymph is formed when blood capillaries in tissues allow water and small soluble molecules to filter out into intercellular spaces due to capillary pressure, forming tissue (interstitial) fluid.
This tissue fluid is collected by an elaborate network of lymphatic vessels (the lymphatic system) and the fluid within this system is called lymph.
Lymph flows through lymph nodes (where pathogens are filtered and lymphocytes are added) and is eventually drained back into major veins through the thoracic duct and right lymphatic duct.
Lymph also transports fats absorbed from intestinal lacteals, hormones, and metabolic waste, playing a crucial role in both nutrition and immune surveillance.

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Long Answer

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Hard

Question 8

Long Form

Explain double circulation in humans. Why is it considered more efficient than single or incomplete circulation?

Double circulation means that blood passes through the heart twice in one complete circuit — once through pulmonary circulation (right side of heart to lungs and back) and once through systemic circulation (left side to body and back).
In pulmonary circulation, deoxygenated blood from the right ventricle is pumped via the pulmonary artery to the lungs, oxygenated, and returned to the left atrium via pulmonary veins.
In systemic circulation, oxygenated blood from the left ventricle enters the aorta, is distributed to all body tissues through arteries, arterioles, and capillaries, and returns via venules, veins, and vena cava to the right atrium.
Because the left and right sides of the heart are completely separated by septa, oxygenated and deoxygenated blood never mix — providing maximum oxygen delivery to tissues.
In contrast, fishes have single circulation (blood oxygenated once and pumped to body), and amphibians/reptiles have incomplete double circulation where blood mixes in the single ventricle, reducing oxygen supply efficiency.
The complete separation of oxygenated and deoxygenated pathways in humans and other mammals supports high metabolic rates and endothermy, making double circulation evolutionarily superior.

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Long Answer

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Hard

Question 9

Long Form

Analyse the significance of the ECG in evaluating cardiac health, describing how each wave correlates with mechanical events in the heart.

The ECG (electrocardiogram) is a graphical record of the electrical activity of the heart during a cardiac cycle, obtained using an electrocardiograph with leads attached to the wrists and left ankle.
The P-wave represents the depolarisation of the atria, which triggers atrial contraction (atrial systole) — the first mechanical event of the cycle.
The QRS complex represents the rapid depolarisation of the ventricles; ventricular contraction begins shortly after Q and produces the powerful ventricular systole that ejects blood into the aorta and pulmonary artery.
The T-wave represents the repolarisation of the ventricles — their return to a resting state; its end marks the conclusion of systole and the onset of ventricular diastole.
By counting QRS complexes per unit time, the heart rate can be determined; the intervals between waves reflect the conduction velocity through different parts of the nodal system.
Deviations from the normal ECG shape for a given lead configuration indicate possible cardiac abnormalities such as arrhythmia, myocardial infarction, or conduction blocks, making ECG of great clinical diagnostic significance.

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Long Answer

Hard difficulty • Structured explanation

Hard

Question 10

Long Form

Describe the regulation of cardiac activity through neural and hormonal mechanisms, and explain how the heart achieves both intrinsic and extrinsic control.

The heart is myogenic — it is intrinsically regulated by specialised nodal tissue (SAN) that generates action potentials autonomously without external stimuli, maintaining a basal rate of 70–75 beats per minute.
This intrinsic auto-regulation means the heart can continue beating even when isolated from the nervous system, as seen in transplanted hearts.
Extrinsic regulation is achieved through a special neural centre in the medulla oblongata that moderates cardiac function via the autonomic nervous system (ANS).
Sympathetic nerve signals increase heart rate, enhance the strength of ventricular contraction, and elevate cardiac output — responses seen during exercise, stress, or emergencies.
Parasympathetic nerve signals (via the vagus nerve) decrease heart rate, slow impulse conduction through the AV node, and reduce cardiac output — dominant during rest and recovery.
In addition, hormones from the adrenal medulla (epinephrine and norepinephrine) can increase cardiac output, providing hormonal reinforcement of sympathetic effects during acute stress.

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Chapter 15: Body Fluids and Circulation | Long Questions

Compare and contrast the composition and functions of the different types of leucocytes, and explain how they collectively defend the body.

Trace the evolutionary changes in the pattern of heart structure and circulation across vertebrates, from fishes to mammals.

Describe the complete sequence of events in a cardiac cycle, including the role of valves and nodal tissue at each stage.

Analyse the mechanism of blood coagulation, naming all key molecules involved and explaining the cascade process.

Explain the ABO and Rh blood grouping systems and discuss why accurate blood grouping is critical before transfusion.

Describe the structure of the human heart, including its chambers, septa, valves, and the nodal tissue system.

Compare the composition and properties of blood and lymph, and explain the route by which lymph is formed and returned to blood.

Explain double circulation in humans. Why is it considered more efficient than single or incomplete circulation?

Analyse the significance of the ECG in evaluating cardiac health, describing how each wave correlates with mechanical events in the heart.

Describe the regulation of cardiac activity through neural and hormonal mechanisms, and explain how the heart achieves both intrinsic and extrinsic control.

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