NCERT Solutions for Class 11 Biology Chapter 15 Body Fluids and Circulation
NCERT Solutions for Class 11 Biology Chapter 15 Body Fluids and Circulation covers revision notes and step-by-step textbook solutions detailing blood composition, blood groups, blood clotting, lymph, human heart structure, cardiac cycle, electrocardiogram (ECG), double circulation, regulation of cardiac activity, and circulatory disorders.
Overview of Topics & Subtopics (Click to Jump)
1. Blood Composition, Groups & Coagulation
Short Note:
• Plasma (~55% of blood): Straw-colored fluid containing 90–92% water and proteins (Fibrinogen for clotting, Globulins for defense, Albumins for osmotic balance).
• Formed Elements (~45% of blood):
- Erythrocytes (RBCs): Biconcave, enucleated in mammals, carry hemoglobin (~5–5.5 million/mm³; lifespan ~120 days).
- Leucocytes (WBCs): Nucleated, defense cells (~6000–8000/mm³). Divided into Granulocytes (Neutrophils, Eosinophils, Basophils) and Agranulocytes (Lymphocytes, Monocytes).
- Thrombocytes (Platelets): Cell fragments from megakaryocytes (~1,500,000–3,500,000/mm³), essential for blood clotting.
• Blood Groups:
- ABO System: Based on surface antigens A and B. Type O is universal donor; Type AB is universal recipient.
- Rh Grouping: Rh positive (+ve) or Rh negative (-ve). Rh incompatibility during pregnancy (Rh⁻ mother with Rh⁺ fetus) can cause Erythroblastosis Fetalis.
• Coagulation of Blood: Injury activates platelets → release Thromboplastin → forms Thrombokinase enzyme → converts inactive Prothrombin to Thrombin (in presence of Ca²⁺) → converts soluble Fibrinogen to insoluble Fibrin threads to form clot.
2. Lymph (Tissue Fluid) & Human Circulatory Pathways
Short Note:
• Lymph (Interstitial Fluid): Colorless fluid containing specialized lymphocytes, lacking RBCs and larger proteins. It transports nutrients, hormones, and absorbs fats via lacteals in intestinal villi.
• Circulatory Patterns:
- Open Circulatory System: Blood pumped by heart passes through large vessels into open spaces or body cavities called sinuses (e.g., Arthropods and Molluscs).
- Closed Circulatory System: Blood is circulated through a closed network of blood vessels (e.g., Annelids and Chordates). Provides more precise blood flow regulation.
3. Human Heart, Cardiac Cycle & Electrocardiogram (ECG)
Short Note:
• Structure of Heart: Four-chambered muscular organ (2 atria, 2 ventricles) enclosed in pericardium. Nodal tissue includes SAN (Sino-atrial node) located in right atrium (pacemaker, generates 70–75 action potentials/min) and AVN (Atrio-ventricular node).
• Cardiac Cycle (Duration ~0.8 sec):
- Joint Diastole: All four chambers relaxed, blood flows from pulmonary veins/vena cava into ventricles through open AV valves (tricuspid/bicuspid).
- Atrial Systole: SAN generates action potential; both atria contract, increasing blood flow into ventricles by ~30%.
- Ventricular Systole: Ventricles contract; AV valves close (producing 1st heart sound 'LUB'); semilunar valves open, pumping blood into aorta and pulmonary artery.
- Ventricular Diastole: Ventricles relax; semilunar valves close (producing 2nd heart sound 'DUB').
• Stroke Volume & Cardiac Output: Stroke volume = ~70 mL per beat. Cardiac Output = Stroke Volume × Heart Rate = 70 mL × 72 = ~5000 mL (5 Litres/min).
• Electrocardiogram (ECG): Graphical representation of electrical activity of heart during cardiac cycle.
- P-wave: Depolarisation (excitation) of atria.
- QRS complex: Depolarisation of ventricles (triggers ventricular contraction).
- T-wave: Repolarisation (return to resting state) of ventricles.
4. Double Circulation & Circulatory System Disorders
Short Note:
• Double Circulation:
- Pulmonary Circulation: Deoxygenated blood from right ventricle → Pulmonary Artery → Lungs → Oxygenated blood → Pulmonary Veins → Left Atrium.
- Systemic Circulation: Oxygenated blood from left ventricle → Aorta → Body Tissues → Deoxygenated blood → Vena Cava → Right Atrium.
- Hepatic Portal System: Vascular connection between digestive tract and liver before blood enters systemic circulation.
• Disorders of Circulatory System:
- Hypertension (High Blood Pressure): Blood pressure higher than normal (120/80 mmHg). Sustained 140/90 mmHg or higher affects heart, brain, and kidneys.
- Coronary Artery Disease (CAD / Atherosclerosis): Deposition of calcium, fat, cholesterol, and fibrous tissue in arteries supplying heart muscle, narrowing their lumen.
- Angina Pectoris: Acute chest pain due to inadequate oxygen reaching heart muscle.
- Heart Failure: State of heart when it does not pump blood effectively enough to meet the body's needs (congestion of lungs is a main symptom).
Intext & Conceptual Questions
• Definition: Erythroblastosis Fetalis is a severe hemolytic disease of the newborn caused by Rh incompatibility between an Rh-negative mother and an Rh-positive fetus.
• Mechanism: During the delivery of the first child, small amounts of Rh⁺ fetal blood may mix with maternal blood, causing the mother to synthesize anti-Rh antibodies. During subsequent Rh⁺ pregnancies, these maternal IgG antibodies cross the placenta into fetal blood, destroying fetal RBCs and leading to severe anemia, jaundice, or fetal death.
• Prevention: Administering anti-Rh antibodies (RhoGAM) to the Rh-negative mother immediately following the delivery of the first Rh-positive child.
The Sino-atrial Node (SAN) is called the pacemaker of the human heart because:
1. It is a specialized nodal tissue that can generate action potentials automatically without external neural stimulation (auto-excitable).
2. It generates the maximum number of action potentials per minute (~70–75 impulses/min).
3. It initiates and maintains the rhythmic contractile activity (pacing) of the entire heart.
Textbook Chapter End Exercise Questions
| Feature | Open Circulatory System | Closed Circulatory System |
|---|---|---|
| Blood Vessels | Blood vessels open into large open spaces called sinuses. | Blood flows through a closed network of blood vessels (arteries, veins, capillaries). |
| Direct Tissue Contact | Body tissues remain in direct contact with circulating fluid (hemolymph). | Blood does not come into direct contact with tissues; exchange occurs via tissue fluid. |
| Regulation & Pressure | Blood flows at low pressure and cannot be regulated precisely. | Blood flows at high pressure, allowing precise regulation of flow rate. |
| Examples | Arthropods, Molluscs. | Annelids, Cephalopods, Vertebrates (Humans). |
| Feature | Arteries | Veins |
|---|---|---|
| Direction of Flow | Carry blood away from heart to various organs. | Carry blood from various organs back toward the heart. |
| Nature of Blood | Carry oxygenated blood (except Pulmonary Artery). | Carry deoxygenated blood (except Pulmonary Vein). |
| Wall & Lumen Structure | Thick, elastic muscular walls with a narrow lumen. | Thinner, less muscular walls with a wide lumen. |
| Internal Valves | Valves are absent (high pressure prevents backflow). | Valves are present to prevent backflow of blood under low pressure. |
Read More & Chapter Resources
These short notes are designed for quick revision. Read the main points once, then use the related material below to practise the same chapter. Revising a concept and checking it with questions can make your preparation more focused.