Chapter 18: Body Fluids and Circulation – Long Answer Type Questions

CBSE Class 11 Biology Long Answer Questions – Body Fluids and Circulation (NCERT)

Course & Examination Details

• Course: CBSE Class 11 Biology
• Prescribed By: Central Board of Secondary Education
• Based On: NCERT
• Unit: Unit V – Human Physiology
• Chapter: Chapter 18 – Body Fluids and Circulation
• Question Type: Long Answer Questions (LAQs)
• Answer Length: 120–150 words
• Exam Relevance: CBSE Class 11 Annual Examination, School Assessments

Section A: Blood (Q1–Q8)

Q1. Describe blood as a connective tissue and explain its functions.

Answer:
Blood is a specialized fluid connective tissue that circulates throughout the human body. It consists of plasma and formed elements and acts as a medium of transport. Blood transports oxygen from lungs to tissues and carbon dioxide from tissues to lungs. It carries nutrients from the digestive tract, hormones from endocrine glands, and metabolic wastes to excretory organs. Blood also helps regulate body temperature by distributing heat. Plasma proteins maintain osmotic balance and blood volume. White blood cells provide defense against pathogens, while platelets play a key role in blood clotting. Thus, blood connects various organs functionally and maintains internal stability or homeostasis.

Q2. Explain the composition of blood in detail.

Answer:
Blood is composed of plasma and formed elements. Plasma constitutes about 55 percent of blood volume and is mainly water. It contains plasma proteins such as albumins, globulins, and fibrinogen. Albumins maintain osmotic balance, globulins are involved in immunity, and fibrinogen aids in clotting. Plasma also transports nutrients, hormones, gases, and waste materials. The formed elements include red blood cells, white blood cells, and platelets. Red blood cells contain haemoglobin and transport oxygen and carbon dioxide. White blood cells provide immunity, while platelets help in blood clotting. Together, these components enable blood to perform transport, regulatory, and protective functions.

Q3. Describe the structure and functions of red blood cells.

Answer:
Red blood cells are biconcave, circular, and enucleated cells found in blood. Their biconcave shape increases surface area for efficient gas exchange and allows flexibility to pass through narrow capillaries. They contain haemoglobin, an iron-containing respiratory pigment. The absence of a nucleus provides more space for haemoglobin, enhancing oxygen-carrying capacity. Red blood cells transport oxygen from lungs to tissues in the form of oxyhaemoglobin and carry a small amount of carbon dioxide back to lungs. Their average lifespan is about 120 days, after which they are destroyed mainly in the spleen and liver.

Q4. Explain the role of white blood cells in body defense.

Answer:
White blood cells are nucleated, colorless cells that play a vital role in immunity. They are classified into granulocytes and agranulocytes. Neutrophils and monocytes perform phagocytosis by engulfing and destroying pathogens. Eosinophils are involved in allergic responses and defense against parasites, while basophils release histamine during inflammation. Lymphocytes are central to immune responses; B-lymphocytes produce antibodies, and T-lymphocytes regulate cell-mediated immunity. White blood cells protect the body from infections, remove dead cells, and help maintain internal defense mechanisms essential for survival.

Q5. Describe the process of blood clotting.

Answer:
Blood clotting is a protective mechanism that prevents excessive blood loss during injury. When a blood vessel is damaged, platelets accumulate at the site and release thromboplastin. In the presence of calcium ions and vitamin K, thromboplastin converts prothrombin into thrombin. Thrombin then converts soluble fibrinogen into insoluble fibrin threads. These fibrin threads form a mesh that traps blood cells, resulting in formation of a clot. The clot seals the wound and prevents further bleeding. After healing, the clot dissolves naturally. This mechanism is essential for maintaining blood volume and preventing fatal blood loss.

Q6. Explain the significance of plasma proteins.

Answer:
Plasma proteins are essential components of blood plasma. Albumins are the most abundant and help maintain osmotic pressure, regulating fluid exchange between blood and tissues. Globulins include antibodies that provide immunity against pathogens. Fibrinogen plays a key role in blood clotting by forming fibrin during coagulation. These proteins also help in transport of substances, buffering of blood pH, and maintenance of blood viscosity. Thus, plasma proteins are crucial for circulatory stability, immune defense, and prevention of excessive blood loss.

Q7. Differentiate between tissue fluid and lymph.

Answer:
Tissue fluid is formed when plasma filters out of capillaries into intercellular spaces. It surrounds body cells and facilitates exchange of nutrients, gases, and wastes. Lymph is formed when excess tissue fluid enters lymphatic vessels. Unlike plasma, lymph contains fewer proteins and no red blood cells. Lymph transports absorbed fats from intestines, returns excess fluid to blood circulation, and plays a role in immunity by carrying lymphocytes. Both fluids support circulation and tissue nourishment but differ in composition and function.

Q8. Explain erythropoiesis and its regulation.

Answer:
Erythropoiesis is the process of formation of red blood cells in the bone marrow. It occurs throughout life to replace aged and destroyed RBCs. This process is regulated by the hormone erythropoietin, secreted mainly by kidneys in response to low oxygen levels in blood. Adequate supply of iron, vitamin B₁₂, and folic acid is essential for normal erythropoiesis. Proper regulation ensures sufficient oxygen transport capacity of blood and prevents disorders such as anaemia.

Section B: Heart & Blood Vessels (Q9–Q16)

Q9. Describe the structure of the human heart.

Answer:
The human heart is a muscular, four-chambered organ located in the thoracic cavity between the lungs. It is enclosed by a double-layered pericardium. The heart consists of two atria and two ventricles separated by septa, preventing mixing of oxygenated and deoxygenated blood. The right atrium receives deoxygenated blood from the body, while the left atrium receives oxygenated blood from lungs. The ventricles pump blood out of the heart. Valves such as tricuspid, bicuspid, and semilunar valves ensure unidirectional flow of blood. This structure supports efficient circulation.

Q10. Explain the working of heart valves.

Answer:
Heart valves regulate the flow of blood through the heart and prevent backflow. The tricuspid valve lies between right atrium and right ventricle, while the bicuspid valve is between left atrium and left ventricle. Semilunar valves are present at the bases of the aorta and pulmonary artery. During atrial systole, atrioventricular valves open to allow blood into ventricles. During ventricular systole, these valves close, producing the first heart sound. Semilunar valves open to allow blood into arteries and close during diastole, producing the second heart sound. Valves ensure efficient circulation.

Q11. Explain the myogenic nature of the human heart.

Answer:
The human heart is myogenic, meaning it generates its own rhythmic impulses for contraction. The sinoatrial (SA) node initiates electrical impulses, acting as the natural pacemaker. These impulses spread across atria, causing atrial contraction. They then reach the atrioventricular (AV) node, which delays the impulse briefly before passing it to ventricles via Bundle of His and Purkinje fibres. This ensures coordinated contraction of atria and ventricles. The autonomic nervous system regulates heart rate but does not initiate the heartbeat.

Q12. Describe different types of blood vessels.

Answer:
Blood vessels form a closed network for blood circulation. Arteries carry blood away from the heart and have thick, elastic walls to withstand high pressure. Veins carry blood towards the heart and have thinner walls with valves to prevent backflow. Capillaries are microscopic vessels with walls one cell thick. They connect arteries and veins and allow exchange of gases, nutrients, and wastes between blood and tissues. Each type of vessel is structurally adapted to its function.

Q13. Explain double circulation in humans.

Answer:
Double circulation refers to blood passing through the heart twice during one complete cycle. It includes pulmonary and systemic circulation. In pulmonary circulation, deoxygenated blood flows from right ventricle to lungs and returns oxygenated to left atrium. In systemic circulation, oxygenated blood flows from left ventricle to body tissues and returns deoxygenated blood to right atrium. Double circulation ensures efficient oxygen supply and prevents mixing of oxygenated and deoxygenated blood.

Q14. Describe coronary circulation.

Answer:
Coronary circulation supplies oxygenated blood to the heart muscles. Coronary arteries arise from the base of the aorta and branch over the heart surface. Coronary veins collect deoxygenated blood from heart muscles and drain it into the right atrium. Adequate coronary circulation is essential for continuous functioning of the heart. Blockage of coronary arteries can lead to coronary artery disease and heart attack.

Q15. Explain hypertension and its effects.

Answer:
Hypertension is a condition of persistently high blood pressure. It increases workload on the heart and damages blood vessels. Prolonged hypertension may lead to heart failure, stroke, and kidney damage. It is often caused by stress, obesity, lack of exercise, or genetic factors. Early detection and lifestyle changes are essential to prevent complications.

Q16. Explain heart failure.

Answer:
Heart failure occurs when the heart is unable to pump sufficient blood to meet the body’s needs. It may result from coronary artery disease, hypertension, or heart muscle damage. Symptoms include fatigue, breathlessness, and fluid accumulation. Proper medical management is required to maintain circulation.

Section C: Cardiac Cycle & Blood Groups (Q17–Q25)

Q17. Explain the cardiac cycle.

Answer:
The cardiac cycle includes all events during one heartbeat and lasts about 0.8 seconds. It consists of atrial systole, ventricular systole, and joint diastole. During atrial systole, atria contract and fill ventricles. Ventricular systole pumps blood into arteries. During joint diastole, all chambers relax and refill with blood.

Q18. Explain heart sounds.

Answer:
Heart sounds are produced by valve closure. The first sound, “lub,” occurs due to closure of atrioventricular valves. The second sound, “dub,” occurs due to closure of semilunar valves.

Q19. Explain regulation of heart rate.

Answer:
Heart rate is regulated by autonomic nervous system. Sympathetic nerves increase heart rate, while parasympathetic nerves decrease it.

Q20. Describe ABO blood group system.

Answer:
ABO system is based on presence of antigens A and B on RBCs and corresponding antibodies in plasma.

Q21. Explain Rh factor and erythroblastosis fetalis.

Answer:
Rh factor determines Rh positive or negative blood. Rh incompatibility between mother and fetus causes erythroblastosis fetalis.

Q22. Importance of blood grouping before transfusion.

Answer:
Blood grouping prevents agglutination and fatal transfusion reactions.

Q23. Explain agglutination.

Answer:
Agglutination is clumping of RBCs due to antigen–antibody reaction.

Q24. Why is AB called universal recipient?

Answer:
Blood group AB lacks antibodies, allowing safe transfusion from all groups.

Q25. Importance of circulation in homeostasis.

Answer:
Circulation maintains internal balance by distributing substances and regulating temperature and pH.

NCERT & CBSE Compliance Note

✔ Strictly based on NCERT Class 11 Biology
✔ Answer length maintained (120–150 words)
✔ Framework-aligned and board-exam focused
✔ Ideal for CBSE Class 11 examinations