Chapter 15 of Class 11 Biology is Body Fluids and Circulation. It covers the composition of blood and lymph, the human heart and cardiac cycle, and blood pressure regulation. These Class 11 Biology Chapter 15 solutions are also useful as quick revision notes before exams.
Blood Composition
Blood consists of plasma (fluid matrix, ~55%, contains proteins like fibrinogen, globulins, albumins) and formed elements (~45%): RBCs/erythrocytes (O₂ transport via haemoglobin), WBCs/leukocytes (immunity — granulocytes and agranulocytes), and platelets/thrombocytes (blood clotting).
Blood Groups
ABO system: based on antigens A/B on RBC surface (groups A, B, AB, O). Rh system: presence/absence of Rh antigen (Rh+/Rh−). Important for safe blood transfusion (avoiding antigen-antibody agglutination reactions).
Blood Clotting (Coagulation)
A protective mechanism involving a cascade of clotting factors, ultimately converting soluble fibrinogen into insoluble fibrin threads (via thrombin), forming a clot to seal the wound and prevent excess blood loss.
Lymph (Tissue Fluid)
A colourless fluid derived from blood plasma that leaks out of capillaries, circulates through the lymphatic system, and returns to the bloodstream; important in fat absorption and immune defence (contains lymphocytes).
Human Heart and Cardiac Cycle
Four-chambered (2 atria, 2 ventricles). The cardiac cycle consists of systole (contraction) and diastole (relaxation), generating the characteristic “lub-dub” heart sounds from valve closure. Heartbeat is myogenic, initiated by the sinoatrial (SA) node (“pacemaker”).
Blood Pressure and ECG
Normal blood pressure: ~120/80 mmHg (systolic/diastolic). Electrocardiogram (ECG) records the electrical activity of the heart (P wave = atrial depolarization, QRS complex = ventricular depolarization, T wave = ventricular repolarization).
Class 11 Biology Chapter 15 – Notes and Extra Questions
Along with these NCERT Solutions, students can also use the Class 11 Biology Chapter 15 Extra Questions and Class 11 Biology Chapter 15 Revision Notes for quick revision and extra practice.
