Body Fluids and Circulation — Class 11 Biology NCERT Solutions (Free)
Free step-by-step NCERT solutions for Class 11 Biology chapter "Body Fluids and Circulation" — 8 important questions with detailed answers for CBSE board exam preparation.
TL;DR: Free step-by-step NCERT solutions for Class 11 Biology chapter "Body Fluids and Circulation" — 8 important questions with detailed answers for CBSE bo…
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NCERT Solutions for Class 11 Biology — Body Fluids and Circulation. Step-by-step answers to all 8 textbook questions from this chapter, written for CBSE board preparation and free to use.
Body Fluids and Circulation — All 8 Questions Solved
Q1. What are the main components of blood?
Blood is a connective tissue consisting of two main components:
1. Plasma (~55% by volume): Liquid matrix; 90% water, 10% solutes (proteins, ions, glucose, hormones, wastes)
2. Cells and cell fragments (~45% by volume):
- Red blood cells (RBCs/erythrocytes): ~5 million/mm³; carry oxygen via hemoglobin
- White blood cells (WBCs/leukocytes): ~5,000-10,000/mm³; immune function
- Platelets (thrombocytes): ~150,000-400,000/mm³; blood clotting
Blood serves transport, immune, and hemostasis (clotting) functions.
Q2. Describe the structure and function of red blood cells.
RBCs (erythrocytes):
Structure: Biconcave disc shape; ~7-8 micrometer diameter; no nucleus in mature RBCs (mammals).
Composition: ~33% hemoglobin, which gives red color; cytoplasm lacks organelles.
Function: Primary function is oxygen transport. One RBC contains ~280 million hemoglobin molecules, each carrying 4 O2 molecules.
Production: Produced in bone marrow via erythropoiesis; lifespan ~120 days; old RBCs destroyed in liver/spleen.
Red blood cell count varies: ~5-6 million/mm³ (males), ~4-5 million/mm³ (females).
Low RBC count causes anemia; high count causes polycythemia.
Q3. What are the types of white blood cells and their functions?
WBCs (leukocytes) are nucleated cells involved in immunity. Main types:
1. Granulocytes (30-40% of WBCs):
- Neutrophils: Most abundant; phagocytose bacteria; form pus
- Eosinophils: Combat parasites; modulate immune response
- Basophils: Release histamine in allergic reactions
2. Monocytes (3-8% of WBCs): Phagocytic; become macrophages in tissues
3. Lymphocytes (20-30% of WBCs): T cells (cell immunity), B cells (antibodies), NK cells
Total WBC count: ~5,000-10,000/mm³. High count indicates infection; low count (leukopenia) indicates compromised immunity.
Q4. Explain blood clotting (hemostasis). What are its stages?
Hemostasis is the process of blood clotting to prevent blood loss. Three stages:
1. Vasoconstriction: Blood vessel constricts, reducing blood flow
2. Platelet plug formation: Platelets adhere to damaged endothelium, aggregate to form temporary plug
3. Coagulation (blood clotting): Cascade of enzyme reactions converts fibrinogen → fibrin (insoluble protein); fibrin forms mesh that stabilizes clot
Coagulation requires:
- Tissue factor (TF) and phospholipids from damaged tissue
- Cofactors: Ca²+ ions, vitamin K
- Clotting factors (numbered I-XIII): Thrombin (Factor II) converts fibrinogen to fibrin
Final step: Cross-linking of fibrin by Factor XIII stabilizes clot; clot retraction occurs.
Anticoagulants (heparin, warfarin) prevent clotting; protease inhibitors prevent excessive clotting.
Q5. Describe the structure of the human heart.
The heart is a muscular, four-chambered organ:
Structure:
- Upper chambers: Right and left atria (receive blood)
- Lower chambers: Right and left ventricles (pump blood)
- Septa: Walls separating left and right sides; interatrial and interventricular septa
- Valves: Tricuspid (right AV valve), Mitral/Bicuspid (left AV valve), Aortic (aortic valve), Pulmonary (pulmonary valve)
Wall layers:
- Epicardium: Outer membrane
- Myocardium: Thick muscular layer
- Endocardium: Inner membrane
Function: Right side pumps deoxygenated blood to lungs; left side pumps oxygenated blood to body.
Average heart rate: 72 beats/minute in adults; cardiac output: ~5 liters/minute.
Q6. Explain the cardiac cycle. What are systole and diastole?
Cardiac cycle is one complete heartbeat (~0.8 seconds at rest, 72 beats/min).
Diastole: Relaxation phase (~0.5 sec); atria and ventricles relax; AV valves open; blood flows from atria into ventricles; semilunar valves closed.
Systole: Contraction phase (~0.3 sec):
- Atrial systole: Atria contract; blood pushed into ventricles
- Ventricular systole: Ventricles contract; AV valves close (produces 'lub' sound); blood pushed into arteries; semilunar valves open
Atrial relaxation follows while ventricles contract.
Double lub-dub sound: 'lub' = closure of AV valves; 'dub' = closure of semilunar valves.
Pressure changes: Ventricular pressure rises during systole, falls during diastole; ensures one-way blood flow.
Q7. What is blood pressure? How is it regulated?
Blood pressure (BP) is the force exerted by blood on artery walls; measured as systolic/diastolic (e.g., 120/80 mmHg).
Systolic: Pressure during ventricular contraction (~120 mmHg)
Diastolic: Pressure during ventricular relaxation (~80 mmHg)
Mean BP = Diastolic + (Systolic - Diastolic)/3 ≈ 93 mmHg
Regulation:
1. Cardiac output: Determined by heart rate and stroke volume
2. Peripheral resistance: Arteriolar constriction/dilation (sympathetic nervous system)
3. Blood volume: Maintained by kidneys (ADH, aldosterone)
4. Blood viscosity: Affected by RBC count and plasma proteins
Nerves (baroreceptors in carotid sinus/aortic arch) and hormones regulate BP moment-to-moment.
Hypertension (>140/90) increases disease risk; hypotension (<90/60) reduces organ perfusion.
Q8. Describe the pulmonary and systemic circulations.
Pulmonary circulation: Carries deoxygenated blood from heart to lungs
- Starts: Right ventricle → Pulmonary artery (divides into left and right) → Lungs
- Returns: Pulmonary veins (4 total) → Left atrium
- Purpose: Gas exchange; oxygenation of blood
- BP is lower (systolic ~25 mmHg) because lungs require less force
Systemic circulation: Carries oxygenated blood from heart to all body tissues
- Starts: Left ventricle → Aorta (branches to all organs) → Capillaries in tissues → Veins → Superior and inferior vena cava → Right atrium
- Purpose: Nutrient and oxygen delivery; waste removal
- BP is higher (systolic ~120 mmHg) to overcome resistance in large circulation
Both circuits operate simultaneously; right and left sides of heart are in series.
Body Fluids and Circulation — Practice MCQs with Answers
Attempt these 20 multiple-choice questions after working through the solutions above. Each carries the correct option and the reasoning behind it, so a wrong answer tells you which idea to revisit.
MCQ 1. What is the primary function of erythrocytes in human blood?
- A. Fighting infections
- B. Transporting oxygen
- C. Blood clotting
- D. Producing antibodies
Answer: B. Transporting oxygen — Erythrocytes, also known as red blood cells, contain hemoglobin which is responsible for binding and transporting oxygen from the lungs to the body tissues.
MCQ 2. A person with 'AB' blood group is considered a universal recipient because:
- A. They have no antigens on RBCs.
- B. They have both A and B antigens on RBCs.
- C. They have no antibodies in plasma.
- D. They have both anti-A and anti-B antibodies in plasma.
Answer: C. They have no antibodies in plasma. — Individuals with AB blood group possess both A and B antigens on their red blood cells but lack anti-A and anti-B antibodies in their plasma, allowing them to receive blood from any ABO blood group.
MCQ 3. Which of the following ions plays a crucial role in blood clotting by activating prothrombin activator and facilitating the conversion of fibrinogen to fibrin?
- A. Sodium ions
- B. Potassium ions
- C. Calcium ions
- D. Chloride ions
Answer: C. Calcium ions — Calcium ions (Ca++) are essential for blood coagulation. They activate the prothrombin activator complex and are required for the conversion of fibrinogen to stable fibrin clots.
MCQ 4. The valve present between the right atrium and the right ventricle is the:
- A. Bicuspid valve
- B. Tricuspid valve
- C. Semilunar valve
- D. Aortic valve
Answer: B. Tricuspid valve — The tricuspid valve, consisting of three cusps, regulates blood flow from the right atrium to the right ventricle, preventing backflow during ventricular contraction.
MCQ 5. The 'lubb' sound of the heart is produced during the closure of which valves?
- A. Aortic and pulmonary valves
- B. Tricuspid and bicuspid valves
- C. Aortic and tricuspid valves
- D. Pulmonary and bicuspid valves
Answer: B. Tricuspid and bicuspid valves — The first heart sound, 'lubb', is associated with the closure of the tricuspid and bicuspid (mitral) valves at the beginning of ventricular systole.
MCQ 6. In a standard ECG, the QRS complex represents:
- A. Atrial repolarization
- B. Ventricular depolarization
- C. Atrial depolarization
- D. Ventricular repolarization
Answer: B. Ventricular depolarization — The QRS complex in an ECG signifies the depolarization of the ventricles, which triggers ventricular contraction. Atrial repolarization occurs simultaneously but is masked by the larger QRS complex.
MCQ 7. Which of the following statements about lymph is incorrect?
- A. Lymph is essentially blood plasma minus blood proteins.
- B. Lymph helps in transporting nutrients and hormones.
- C. Lymph has a similar mineral composition to plasma.
- D. Lymph contains a high concentration of red blood cells.
Answer: D. Lymph contains a high concentration of red blood cells. — Lymph is a fluid connective tissue that lacks red blood cells and large proteins, unlike blood. It contains white blood cells (lymphocytes), nutrients, and metabolic waste.
MCQ 8. Which component of blood is primarily responsible for immunity and defense against pathogens?
- A. Erythrocytes
- B. Leukocytes
- C. Platelets
- D. Plasma
Answer: B. Leukocytes — Leukocytes, or white blood cells, are the primary cellular components of the immune system, responsible for identifying and destroying pathogens, foreign invaders, and abnormal cells.
MCQ 9. In humans, the pulmonary circulation carries:
- A. Oxygenated blood from the heart to the lungs.
- B. Deoxygenated blood from the heart to the body parts.
- C. Deoxygenated blood from the heart to the lungs.
- D. Oxygenated blood from the lungs to the body parts.
Answer: C. Deoxygenated blood from the heart to the lungs. — Pulmonary circulation involves the pumping of deoxygenated blood from the right ventricle of the heart to the lungs for oxygenation and then returning oxygenated blood to the left atrium.
MCQ 10. Angina Pectoris is a symptom of an acute chest pain due to:
- A. Insufficient blood supply to the brain.
- B. Insufficient oxygen reaching the heart muscle.
- C. Blood clot in the pulmonary artery.
- D. Inflammation of the pericardium.
Answer: B. Insufficient oxygen reaching the heart muscle. — Angina Pectoris is characterized by severe chest pain that occurs when the heart muscle does not receive enough oxygen-rich blood, often due to narrowing of coronary arteries.
MCQ 11. Which blood type is considered the universal donor in the ABO system?
- A. A
- B. B
- C. AB
- D. O
Answer: D. O — Blood group O is considered the universal donor because its red blood cells lack A and B antigens, making them compatible with all other ABO blood groups without eliciting an immune response in the recipient.
MCQ 12. Which type of blood vessel carries blood away from the heart?
- A. Veins
- B. Arteries
- C. Capillaries
- D. Venules
Answer: B. Arteries — Arteries are thick-walled blood vessels that carry oxygenated blood away from the heart to various parts of the body, except for the pulmonary artery which carries deoxygenated blood to the lungs.
MCQ 13. During the cardiac cycle, ventricular systole begins shortly after the P wave and ends just before the T wave. Which event marks the end of ventricular systole?
- A. Closure of AV valves
- B. Opening of semilunar valves
- C. Closure of semilunar valves
- D. Opening of AV valves
Answer: C. Closure of semilunar valves — Ventricular systole ends with the closure of the semilunar valves (aortic and pulmonary valves), which prevents backflow of blood into the ventricles as they relax, producing the 'dubb' sound.
MCQ 14. Which plasma protein is primarily involved in maintaining osmotic balance?
- A. Fibrinogen
- B. Globulins
- C. Albumins
- D. Prothrombin
Answer: C. Albumins — Albumins are the most abundant plasma proteins and play a crucial role in maintaining the osmotic pressure of the blood, thereby regulating fluid balance between blood and interstitial fluid.
MCQ 15. How many chambers does a human heart have?
- A. Two
- B. Three
- C. Four
- D. Five
Answer: C. Four — The human heart is a four-chambered organ, consisting of two upper atria (receiving chambers) and two lower ventricles (pumping chambers).
MCQ 16. A prolonged P-R interval in an ECG typically indicates a problem with:
- A. Ventricular contraction
- B. Atrial depolarization
- C. Conduction through the AV node
- D. Ventricular repolarization
Answer: C. Conduction through the AV node — The P-R interval represents the time taken for the electrical impulse to travel from the atria through the AV node to the ventricles. A prolonged P-R interval suggests a delay or block in conduction through the AV node.
MCQ 17. The heart rate is primarily regulated by the:
- A. Cerebrum
- B. Cerebellum
- C. Medulla oblongata
- D. Hypothalamus
Answer: C. Medulla oblongata — The heart rate is regulated by the cardiovascular center located in the medulla oblongata of the brainstem, which can increase or decrease heart rate and contractility through sympathetic and parasympathetic nerves.
MCQ 18. The lymphatic system plays a crucial role in:
- A. Transporting oxygen
- B. Blood clotting
- C. Immunity and fluid balance
- D. Producing hormones
Answer: C. Immunity and fluid balance — The lymphatic system is essential for maintaining fluid balance by returning interstitial fluid to the bloodstream and plays a vital role in the body's immune defense by producing and transporting lymphocytes.
MCQ 19. Which of the following is an anti-coagulant naturally present in human blood that prevents spontaneous clotting?
- A. Thromboplastin
- B. Fibrinogen
- C. Heparin
- D. Thrombin
Answer: C. Heparin — Heparin is a natural anticoagulant produced by mast cells in the body. It inhibits blood clotting by enhancing the activity of antithrombin III, which inactivates several clotting factors, including thrombin.
MCQ 20. The process of formation of all blood cellular components is known as:
- A. Hemostasis
- B. Hemolysis
- C. Hematopoiesis
- D. Hemoglobinization
Answer: C. Hematopoiesis — Hematopoiesis is the process by which all blood cells (erythrocytes, leukocytes, and platelets) are formed, developed, and matured from hematopoietic stem cells, primarily in the bone marrow.
How to Use These Solutions
Attempt each question yourself first and only then compare with the worked answer. Marks in the CBSE board exam are awarded for the METHOD as much as the final result, so reproduce the steps rather than memorising the last line. Where a solution states a law, a formula or a definition, learn that wording — examiners look for it.
Related practice for this chapter: chapter MCQs, previous-year questions, revision notes and sample papers.