NCERT Class 11-Biology: Chapter –18 Body Fluids and Circulation Part 5

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Question 4:

Explain the advantage of the complete partition of ventricle among birds and mammals and hence leading to double circulation.


1. Birds and mammals have four chambered heart. Which are two atria and two ventricles.

2. The two atria are separated by inter-atrial septum and the two ventricles are separated by inter-ventricular septum.

3. Oxygenated blood received by the left atria passes to the left ventricle and Deoxygenated blood received by the right atria passes to the right ventricle without getting mixed

4. The blood is circulated to the body organs through the systemic circulation and to the lungs through Pulmonary circulation.

5. This shows that birds and mammals have two separate circulatory pathways which are Systemic and Pulmonary Pathway

Advantage of Double Circulation:

1. Deoxygenated and oxygenated blood remains separated and do not mix.

Question 5:

What is the significance of hepatic portal system in the circulatory system?


The vascular connection that exists between the digestive tract and liver is known as Hepatic Portal System. The hepatic portal system directs deoxygenated blood from the parts of gastrointestinal tract to the liver and finally taking it to the heart.


1. It provides liver with metabolic substrates.

2. It ensures that substances are first processed by liver before reaching systemic circulation.

Question 6:

Explain the functional significance of lymphatic system?


Lymphatic system is a network of vessels which passes through all organs to allow the movement of a fluid called lymph.

Main organs of Lymphatic System are

1. Thymus

2. Spleen

3. Appendix

4. Tonsils

Functional significance of lymphatic system:

1. The fluid lymph carries hormones and nutrients.

2. It maintains fluid balance between blood and tissues also known as fluid haemostasis.

3. Fat absorption takes place through lymph.

4. It renews Extra Cellular Fluid (ECF).

5. Maturation of B and T lymphocytes take place with the help pf lymph.

Question 7:

Write the features that distinguish between the two

a. Plasma and Serum

b. Open and closed circulatory system

c. Sino-atrial node and Atria-ventricular node



Plasma and Serum



(i) The fluid without blood corpuscles is called plasma

(i) The fluid without clotting elements is called serum.

(ii) Fibrinogen and other clotting materials are present.

(ii) Clotting materials are absent.

(iii) Plays important role in blood clotting

(iii) Has no role in blood clotting


Open and closed circulatory system

Open circulatory system

Closed circulatory system

(i) Blood is directly showered on target organs

(i) Blood is supplied to organs through a closed network of vessels.

(ii) Respiratory pigment is absent in most of the cases

(ii) Respiratory pigment is present in all cases.

(iii) Present in arthropods and molluscs

(iii) Present in annelids, some molluscs and all vertebrates.


Sino-atrial node and Atria-ventricular node

Sino-atrial Node

Atrio-ventricular Node

(i) Present on the upper side of the right auricle

(i) Present at the junction of right auricle and right ventricle.

(ii) Initiates the heartbeat

(ii) Takes impulse from SA node and forwards it further.

Question 8:

Thrombocytes are essential for coagulation of blood. Comment.


1. Thrombocytes are also known as Platelets and are found in blood.

2. They are formed in the bone marrow.

3. When an injury occurs, bleeding starts taking place.

4. This causes platelets to disintegrate and start releasing Clotting Factor III, also known as Thromboplastin.

5. Thromboplastin in the presence of calcium ions activate Prothrombokinase. Which further leads to a series of reactions causing blood clot.