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Class 11-science NCERT Solutions Biology Chapter 15 - Body Fluids And Circulation

Body Fluids And Circulation Exercise 204

Solution 1

The formed elements of the blood are

  • Red blood cells (Erythrocytes)
  • White blood cells (Leucocytes)
  • Blood platelets (Thrombocytes)
  • Functions of red blood cells:
    • RBCs are oxygen carriers. They contain haemoglobin which is the respiratory pigment. Haemoglobin combines with oxygen to form oxyhaemoglobin which carries oxygen to regions of lower oxygen concentration in the body.
  • Functions of white blood cells:
    • Neutrophils perform a defence mechanism against bacteria called phagocytosis.
    • Lymphocytes produce antibodies which kill or neutralise germs.
  • Functions of blood platelets:

    Blood platelets help in blood coagulation.

Solution 2

  • The major plasma proteins are fibrinogens, globulins and albumins.
  • Fibrinogen is a necessary factor for blood coagulation.
  • Globulins, also called immunoglobulins, are involved in defence mechanisms of the body.
  • Albumin helps in maintaining the osmotic balance of the body.


Solution 3

Column I

Column II

(a)         Eosinophils

(iii) Resist infections

(b)         RBC

(v) Gas transport

(c)         AB group

(ii) Universal recipient

(d)         Platelets

(i) Coagulation

(e)         Systole

(iv) Contraction of heart

Solution 4

  • Connective tissues bind, link or support the other organs of the body.
  • They are the most abundant and widely distributed tissue in the body.
  • Blood transports gases, nutrients and hormones from one body organ to the other.
  • It flows throughout the body.
  • Hence, blood is considered a connective tissue. 

Solution 5



1. Blood is red liquid connective tissue.  1. Lymph is a white tissue fluid
 2. It flows through blood vessels—arteries, veins and capillaries.

 2. It flows in the lymph vessels.

 3. It contains haemoglobin, red blood cells, white blood cells and platelets.  3. It contains white blood cells called lymp`hocytes.
4. It transports gases and other nutrients in the body  4. Exchange of gases and nutrients between the blood and the cells occurs through the lymph.

Solution 6

  • In double circulation, blood circulates in the heart twice.
  • This is possible because the heart is divided into right and left halves by the atrioventricular septum.


  • Pulmonary Circulation:
    • Blood in the right ventricle is pumped into the pulmonary arteries.
    • The pulmonary arteries carry the deoxygenated blood to the lungs for oxygenation.
    • Oxygenated blood from the lungs is sent to the left atrium via pulmonary veins.
    • This circulation of blood via pulmonary blood vessels is called pulmonary circulation.
  • Systemic Circulation:
    • It pertains to the major circulation of the body.
    • Oxygenated blood from the left ventricle is pumped into the aorta.
    • It is further carried by the arteries, the arterioles and the network of blood capillaries.
    • On the other side, deoxygenated blood is collected in the right atrium through the superior and inferior vena cavae.
    • Systemic circulation provides oxygen and nutrients and carries away carbon dioxide and other harmful substances for elimination.

Significance of double circulation:

  • It prevents the mixing of oxygenated and deoxygenated blood.
  • There is optimum use of oxygen in double circulation.

Solution 7(a)



1. Blood is red liquid connective tissue. 1. Lymph is a white tissue fluid.
2. It flows through blood vessels–arteries, veins and capillaries.
2. It flows in the lymph vessels.
3. It contains haemoglobin, red blood cells, white blood cells and platelets.
3. It contains white blood cells called lymphocytes.
4. It transports gases and other nutrients in the body.
4. The exchange of gases and nutrients between the blood and the cells occurs through the lymph.



Solution 7(b)

Open System of Circulation

Closed System of Circulation

1. Blood pumped by the heart bathes the sinuses (body cavities),

1. Blood pumped by the heart flows through the closed network of blood vessels.

2. The flow of blood may not be regulated accurately.

2. The flow of blood is regulated accurately.

3. There is a direct exchange of gases and nutrients between blood and body cells.

3. The exchange of gases and nutrients between blood and body cells occurs via tissue fluid.

4. It is found in arthropods and molluscs.

4. It is found in annelids and chordates.


Solution 7(c)



1. It is the contraction of heart chambers.

1. It is the relaxation of heart chambers.

2. It increases the blood pressure inside the heart.

2. The blood pressure in the heart falls.

3. Blood is pumped out of the chambers which are in systole.

3. Blood is received by the chambers which are in diastole.


Solution 7(d)



1. It represents the depolarisation or electrical excitation of atria.

1. It represents the repolarisation of ventricles.

2. Blood is pumped into the ventricles.

2. Blood is received by the atria.


Solution 8

  • The vertebrate heart has evolved from a two-chambered heart of a fish to a four-chambered heart of mammals and birds.
  • The heart of fish is two-chambered. The heart pumps deoxygenated blood to the gills where it is oxygenated and sent to the body. The deoxygenated blood is carried to the heart.
  • In amphibians, there are three chambers—the left atrium, the right atrium and a ventricle. The left atrium receives the oxygenated blood from the gills, the lungs or the skin. The right atrium receives deoxygenated blood from the body organs. However, eventually, both types of blood are mixed in the ventricle and the body is supplied with the mixed blood.
  • In case of reptiles, there is half septum which divides the ventricle incompletely. Here, oxygenated and deoxygenated blood do not mix.
  • In crocodiles, birds and mammals, the heart is completely divided into halves which keep the oxygenated and deoxygenated blood separate.
  • There is a structural modification in the heart from fish to mammals, which ensures the supply of oxygenated blood to the body. At the same time, the four-chambered structure makes sure that the flow of blood is regulated.
  • The types of circulation also change from single to double as the structure of the heart is modified.

Solution 9

  • Modified cardiac muscles or the nodal tissue of the heart—the SA node—can generate an impulse which spreads over the walls of the heart.
  • This results in beating of the heart. The meaning of ‘myo’ is ‘muscle’ and ‘genic’ is ‘originating from’.
  • Because the cardiac impulse originates in the heart muscles, it is called myogenic.


Solution 10

  • The sino-atrial node generates the action potential and produces the cardiac impulse.
  • This cardiac impulse then spreads over atria and ventricles causing them to contract or relax.
  • The SA node can generate a maximum number of action potentials which is about 70−75 per minute.
  • It also controls the rhythmic contractile activity of the heart.
  • Because of the property of originating a cardiac impulse, the sino-atrial node is called the pacemaker of the heart.

Solution 11

  • The atrioventricular node picks up the cardiac impulse from the SA node.
  • The atrioventricular bundle which originates from the AV-node conveys the cardiac impulse further towards the walls of the ventricles.

Solution 12

Cardiac Cycle:

  • The circulation of blood in the heart occurs because of the alternate contraction and relaxation of the heart chambers.
  • Contraction is also known as systole, while relaxation is known as diastole.
  • Each contraction phase (systole) is followed by a relaxation or expansion phase (diastole).
  • The series of events which occur during one complete beat of the heart is called the cardiac cycle.
  • The duration of one cardiac cycle is 0.8 seconds.

Cardiac Output:

  • The amount of blood pumped by each ventricle per minute is called the cardiac output.
  • begin mathsize 12px style Cardiac text   end text output text   end text equals text   end text Stroke text   end text volume text   end text cross times text   end text No. text   end text of text   end text heart text   end text beats text   end text per text   end text minute end style

Solution 13

  • Two sounds, lub and dub, are heard during each cardiac cycle.
  • They occur in sequence with each heartbeat.
  • The first sound lub is caused by the closure of the bicuspid and tricuspid valves. It is low pitched.
  • The second sound dub is caused by the closure of semi-lunar valves. It is high pitched.
  • Both sounds are important in clinical diagnosis of any heart-related disorder.


Solution 14

  • ECG (or electrocardiogram) is the graphical representation of the electrical activity of the heart during a cardiac cycle.




  • A typical ECG of a healthy person shows five waves—P, Q, R, S and T.
  • P-wave:
    • It represents the electrical excitation generated by the SA node which causes the depolarisation of the atria.
    • Interval PQ represents the atrial systole.
  • QRS complex:
    • It indicates the spreading of impulse of contraction from the AV node to the walls of the ventricles which causes depolarisation of the ventricles.
    • RS of the QRS complex and ST indicate a ventricular systole.
    • One can determine the heartbeat rate of an individual by counting the number of QRS complexes.
  • T-wave:
    • It represents the repolarisation or relaxation of ventricles.
    • The end of the T-wave marks the end of the systole. 
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