Class 11 Biology

Circulatory System

NCERT Solution

Question 1: Name the components of the formed elements in the blood and mention one major function of each of them.

Answer: Functions of formed elements of blood are as follows:

Function of Erythrocytes (RBCs): transport of respiratory gases.

Functions of Leucocytes (WBCs):

Function of Platelets: Coagulation of blood.

Question 2: What is the importance of plasma proteins?

Answer: The major plasma proteins are; fibrinogen, globulins and albumins. Fibrinogen play important role in blood coagulation. Globulins are mainly involved in defense mechanism and albumins help in osmotic balance.

Question 3: Match Column I with Column II:

Column IColumn II
(a) Eosinophils (1) Coagulation
(b) RBC (2) Universal recipient
(c) AB group (3) Resist infections
(d) Platelets(4) Contraction of heart
(e) Systole(5) Gas transport

Answer: (a) 3, (b) 5, (c) 2, (d) 1, (e) 4

Question 4: Why do we consider blood as a connective tissue?

Answer: Blood is mesodermally derived; as other connective tissues. Blood serves the purpose of connecting the body systems; by transporting substances. Moreover, blood too has a matric; like other connective tissues. Hence, blood is considered as a connective tissue.

Question 5: What is the difference between lymph and blood?


Lymph is interstitial fluid.Blood flows through closed vessels.
WBCs are present.WBCs and RBCs are present.
It is colourless.It is of red colour.

Question 6: What is meant by double circulation? What is its significance?

Answer: Complete double circulation is present in birds and mammals. In this case, the oxygenated blood is received by the left atrium and the deoxygenated blood is received by the right atrium. The oxygenated blood is pumped out through the left ventricle, while the deoxygenated blood is pumped out through the right ventricle. In complete double circulation, there are two separate pathways for oxygenated and deoxygenated bloods. There is complete separation of oxygenated and deoxygenated blood in case of complete double circulation. This provides better efficiency to the organism in terms of energy generation.

Question 7: Write the differences between:

(a) Open and Closed system of circulation

Answer: The organs are directly bathed in blood in case of open circulatory system. In case of closed circulatory system, the blood is channelized through closed vessels.

(b) Systole and Diastole

Answer: Contraction of heart muscles is called systole, while dilatation is called diastole.

(c) P-wave and T-wave

Answer: P-wave marks the depolarization of atria, while T-wave marks the return of ventricles to repolarised state.

Question 8: Describe the evolutionary change in the pattern of heart among the vertebrates.

Answer: A muscular chambered heart is present in all vertebrates. The fishes have a 2-chambered heart; with an atrium and a ventricle. Amphibians and reptiles have a 3-chambered heart; with two atria and one ventricle. But crocodiles have 4-chambered heart. Birds and mammals have 4-chambered heart; with two atria and two ventricles.

Question 9: Why do we call our heart myogenic?

Answer: Normal activities of the heart are intrinsically regulated, i.e. auto regulated by the nodal tissues. Due to this, the heart is called myogenic.

Question 10: Sino-atrial node is called the pacemaker of our heart. Why?

Answer: The SA Node is responsible for initiating and maintaining the rhythmic contractile activity or beating of the heart. Due to this, the SA Node is called the pacemaker.

Question 11: What is the significance of atrio-ventricular node and atrio-ventricular bundle in the functioning of heart?

Answer: AV Node and AV Bundles are responsible for conduction of heart beat to different parts of the heart after initiation in the SA node.

Question 12: Define a cardiac cycle and the cardiac output.

Answer: Cardiac Cycle: The sequential contraction and dilatation of different chambers of heart in a cyclical manner is called cardiac cycle.

Cardiac Output: The volume of blood pumped by the heart in one minute is called the cardiac output. The average cardiac output is 5000 ml or 5 litre per minute.

Question 13: Explain heart sounds.

Answer: Lub and Dub Sounds: Two prominent sounds are produced during each cardiac cycle. These sounds can be easily heard through a stethoscope. The first sound is called lub and is associated with the closure of the tricuspid and bicuspid valves. The second sound is called dub and is associated with the closure of the semi-lunar valves. These sounds are important for clinical diagnosis.

Question 14: Draw a standard ECG and explain the different segments in it.

Answer: Each peak in the ECG is identified with a letter from P to T (PQSRT) which corresponds to a specific electrical activity of the heart.

The P-wave represents the electrical excitation or depolarization of the atria. Depolarisation of atria leads to atricular systole.

The QRS complex represents the depolarization of the ventricles which initiates ventricular systole.

The T-wave represents the return of the ventricles from excited to normal state (repolarisation). The end of T-wave marks the end of systole.

figure of ecg

REF: Wikipedia