Summary
Blood is a connective tissue comprising plasma (55% of blood) and formed elements (45%) including red blood cells, white blood cells, and platelets. Lymph is a colorless fluid derived from tissue fluid that helps transport nutrients and fats, while the circulatory system ensures continuous delivery of oxygen and nutrients to cells and removal of waste through two separate pathways in humans.
Chapter 15 covers the composition and transport functions of body fluids in humans. Blood consists of plasma (90-92% water with proteins like fibrinogen, globulins, and albumins) and formed elements: red blood cells for gas transport (5-5.5 million/mm³), white blood cells for immune defense (6,000-8,000/mm³), and platelets for blood clotting. Blood is grouped by ABO and Rh antigens for transfusion compatibility. Lymph, derived from tissue fluid filtered through capillaries, carries nutrients and immune cells. The human circulatory system features a four-chambered heart with specialized nodal tissue (SAN as pacemaker generating 70-75 beats/min), conducting double circulation: pulmonary circulation delivers deoxygenated blood to lungs, while systemic circulation supplies oxygenated blood to body tissues.
Key points & formulas
- 01Blood comprises plasma (55%) and formed elements—RBCs (gas transport), WBCs (immunity), platelets (clotting)—with ABO and Rh antigen grouping for transfusions
- 02The sino-atrial node (SAN) acts as the heart's pacemaker, generating 70-75 action potentials per minute and maintaining normal heart rate of 72 beats/minute
- 03Cardiac cycle consists of atrial and ventricular systole (contraction) and diastole (relaxation), with heart valves preventing backward blood flow
- 04Double circulation involves two pathways: pulmonary circulation (right ventricle → lungs → left atrium) and systemic circulation (left ventricle → body tissues → right atrium)
- 05Lymph is a colorless tissue fluid containing lymphocytes for immunity, serving as transport medium for nutrients and fats absorbed in the intestines
- 06Blood clotting occurs through cascade enzymatic reactions converting fibrinogen to fibrin, forming networks that trap blood cells at wound sites
Frequently asked questions
01What are the main components of blood and their functions?
Blood comprises plasma (55%) and formed elements (45%). Plasma contains 90-92% water, 6-8% proteins (fibrinogen for clotting, globulins for defense, albumins for osmotic balance), and dissolved minerals and nutrients. Formed elements include: RBCs (~5-5.5 million/mm³) containing hemoglobin for oxygen transport; WBCs (6,000-8,000/mm³) including neutrophils, lymphocytes, eosinophils, and monocytes for immune defense; and platelets (1.5-3.5 million/mm³) for blood clotting.
02What is the difference between systole and diastole in the cardiac cycle?
Systole is the contraction phase of the heart chambers, which begins with atrial systole (both atria contract simultaneously) increasing blood flow into ventricles by 30%, followed by ventricular systole (ventricles contract) that forces blood into pulmonary arteries and aorta. Diastole is the relaxation phase where chambers fill with blood. During a complete cardiac cycle lasting 0.8 seconds, the heart beats once (72 beats/minute in healthy adults).
03How does double circulation work in humans?
Double circulation consists of two separate pathways: pulmonary circulation (right ventricle pumps deoxygenated blood to lungs via pulmonary artery; oxygenated blood returns to left atrium via pulmonary veins) and systemic circulation (left ventricle pumps oxygenated blood via aorta to all body tissues; deoxygenated blood returns to right atrium via vena cava). This separation ensures efficient oxygen delivery and prevents mixing of oxygenated and deoxygenated blood.
04Is the NCERT Class 11 Biology Chapter 15 PDF free to download?
Yes, the NCERT Class 11 Biology Chapter 15 PDF is free to download.
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