The Circulatory System
ICSE Class 10 · Biology · Chapter 8
What this chapter covers
- Blood and its liquid part, plasma
- Composition of blood: the blood cells
- Blood coagulation
- Tissue fluid, lymph and the lymphatic system
- Lymphatic organs: spleen and tonsils
- Structure of the heart
- Working of the heart: systole and diastole
- Blood vessels: artery, vein and capillary
- Circulation of blood and double circulation
- Significance of the hepatic portal system
- Pulse and blood pressure
- ABO blood groups and the Rh factor
Key points
- The circulatory system (heart, blood vessels, blood, lymph) carries oxygen, food, wastes, hormones and heat around the body.
- Blood is 55 per cent plasma and 45 per cent cells; plasma is 90 to 92 per cent water with proteins, food, salts, wastes and hormones.
- Red cells carry oxygen as oxyhaemoglobin; mammalian red cells lack nucleus, mitochondria, ER and Golgi body, which gives more room for haemoglobin and saves the oxygen they carry.
- White cells defend the body by phagocytosis and antibody production; platelets start clotting.
- Clotting: thromboplastin + Ca2+ turns prothrombin into thrombin; thrombin turns fibrinogen into fibrin threads, which trap cells as a clot.
- Tissue fluid leaks from capillaries and bathes cells; in the lymph vessels it becomes lymph, which returns to the blood, carries fats and contains lymphocytes.
- The spleen destroys old red cells, makes lymphocytes and stores blood; tonsils trap germs in the throat.
- The heart has four chambers and four valves (tricuspid, bicuspid, two semilunar); the left ventricle has the thickest wall.
- Venae cavae enter the right atrium, the pulmonary artery leaves the right ventricle, pulmonary veins enter the left atrium and the aorta leaves the left ventricle.
- Systole is contraction and diastole relaxation; one cardiac cycle lasts about 0.8 s; lubb and dubb come from valves closing.
- Arteries are thick, elastic and carry blood away from the heart; veins are thin, have valves and carry blood to the heart; capillaries are one cell thick and are the sites of exchange.
- Double circulation means blood passes through the heart twice per round, keeping oxygenated and deoxygenated blood apart.
- Liver: in by hepatic artery and hepatic portal vein, out by hepatic vein. Kidney: in by renal artery, out by renal vein.
- The hepatic portal system sends food-rich blood from the gut through the liver first, which controls glucose, deals with amino acids and removes toxins.
- Pulse is the rhythmic stretching of arteries at each heartbeat (about 72 per minute); normal blood pressure is 120/80 mm Hg.
Questions answered
Define blood and state the percentage of plasma in it.
Blood is a fluid connective tissue of cells suspended in a liquid matrix, plasma, which circulates through the heart and vessels. Plasma forms about 55 per cent of blood.
Give three reasons why mammalian red blood cells are efficient carriers of oxygen.
No nucleus, ER or Golgi body, so more room for haemoglobin; no mitochondria, so they respire anaerobically and do not use the oxygen they carry; biconcave shape gives a large surface area for diffusion and flexibility to pass through narrow capillaries.
Name the substance released at a wound that starts clotting, and state the role of calcium.
Thromboplastin. Along with calcium ions, it converts prothrombin into thrombin.
Why does blood not normally clot inside the blood vessels?
The undamaged lining releases no thromboplastin, and the anticoagulant heparin is present in the blood.
Distinguish between tissue fluid and lymph.
Tissue fluid is the fluid that leaks out of capillaries and lies between the cells; lymph is the same fluid after it has entered the lymph vessels, where it carries many lymphocytes.
State two functions of the spleen and one of the tonsils.
The spleen destroys worn-out red cells and produces lymphocytes (it also stores blood). The tonsils trap and destroy germs entering through the mouth and nose.
Why is the wall of the left ventricle thicker than that of the right ventricle?
The left ventricle pumps blood to the whole body against high resistance, while the right ventricle pumps only to the nearby lungs.
Name the vessels that (a) bring blood to the right atrium, (b) take blood to the lungs, (c) bring blood to the left atrium.
(a) Superior and inferior venae cavae (and the coronary sinus); (b) pulmonary artery; (c) pulmonary veins.
Past board exam questions
ICSE 2027 sample paper · 1 mark
The path of blood flow during pulmonary circulation is:
- Right auricle, Right ventricle, Pulmonary artery, Lungs, Pulmonary veins, Left auricle.
- Left auricle, Left ventricle, Pulmonary veins, Lungs, Pulmonary artery, Right auricle.
- Left auricle, Left ventricle, Aorta, Tissues, Vena cava, Right auricle.
- Right auricle, Right ventricle, Pulmonary veins, Lungs, Pulmonary artery, Left auricle.
Show answer
Right auricle, Right ventricle, Pulmonary artery, Lungs, Pulmonary veins, Left auricle.
ICSE 2027 sample paper · 1 mark
Assertion (A): Pericardial fluid is present between the heart and pericardium. Reason (R): The human heart has four chambers.
- (A) is true and (R) is false.
- (A) is false and (R) is true.
- Both (A) and (R) are true, and (R) is the correct explanation of (A).
- Both (A) and (R) are true, but (R) is not the correct explanation of (A).
Show answer
Both (A) and (R) are true, but (R) is not the correct explanation of (A).
ICSE 2027 sample paper · 5 marks
Choose the ODD term out from each of the following set of terms. Mention the category to which the remaining three belong: (a) Neutrophil, Monocyte, Eosinophil, Basophil (b) TSH, ADH, ACTH, FSH (c) Wisdom tooth, Pinna, Tongue, Vermiform appendix (d) Haemoglobin, Fibrin, Prothrombin, Fibrinogen (e) Vas deferens, Endometrium, Seminiferous tubule, Vas efferens
Show answer
(a) Odd – Monocyte; Category – Granulocytes
(b) Odd – ADH; Category – Hormones secreted by the anterior lobe of the pituitary gland
(c) Odd – Tongue; Category – Vestigial organs
(d) Odd – Haemoglobin; Category – Components of blood clotting
(e) Odd – Endometrium; Category – Parts of the male reproductive system
ICSE 2027 sample paper · 3 marks
Draw a neat, labelled diagram of a human blood smear.
Show answer
Diagram: many small circular biconcave red blood cells without nuclei, a few larger white blood cells with nuclei (e.g. neutrophil with multi-lobed nucleus, lymphocyte with large round nucleus, monocyte with kidney-shaped nucleus), and small platelets in clusters. Labels: RBC (erythrocyte), WBC (neutrophil/lymphocyte/monocyte), platelets, plasma.
ICSE 2026 board paper · 1 mark
During the ventricular systole, the atrioventricular valves (P) __________ and the semilunar valves (Q) __________.
- P – close and Q – open
- P – close and Q – close
- P – open and Q – close
- P – open and Q – open
Show answer
P – close and Q – open
ICSE 2026 sample paper · 1 mark
Allen’s blood report showed an abnormal decrease in the number of R.B.C. He is suffering from:
- Polycythemia
- Erythropenia
- Glycosuria
- Haemophilia
Show answer
Erythropenia
ICSE 2026 board paper · 1 mark
Assertion(A): Leukoderma is the biological term for blood cancer. Reason(R): An abnormal increase in the number of WBCs causes blood cancer.
- (A) is true and (R) is false.
- (A) is false and (R) is true.
- Both (A) and (R) are true and (R) is the correct explanation of (A).
- Both (A) and (R) are true but (R) is not the correct explanation of (A).
Show answer
(A) is false and (R) is true.
ICSE 2026 sample paper · 1 mark
The cell given here is that of a Neutrophil (a white blood cell with granular cytoplasm and a nucleus of three lobes joined by thin strands). The function is ___________:
- secreting hormone
- transporting food
- phagocytosis
- producing antibodies
Show answer
phagocytosis