NCERT Solutions for Class 11 Biology Chapter 15 Body Fluids and Circulation

NCERT
SOLUTIONS
CLASS - 11th

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Class : 11th
Subject : Biology
Chapter : 18
Chapter Name : Body Fluids And Circulation

Q1 Name the components of the formed elements in the blood and mention one major function of
each of them.

Answer. The component elements in the blood are:
(1) Erythrocytes: They are the most abundant cells and contain the red pigment called
haemoglobin. They carry oxygen to all parts of the body. Red blood cells are produced
continuously in some parts of the body such as the marrow of long bones, ribs, etc. There are
about 4 — 6 million RBCs per cubic millimetre of blood.
(2) Leukocytes : Leucocytes are colourless cells. These cells do not contain haemoglobin. They are
the largest cells of the body and are divided into two main categories.
(a) Granulocytes : These leucocytes have granules in their cytoplasm and include neutrophils,
eosinophils, and basophiles. Neutrophils are phagocytic cells that protect the body against various
infecting agents. Eosinophils are associated with allergic reactions, while basophiles are involved
in in ammatory responses.
(b) Agranulocytes : Lymphocytes and monocytes are agranulocytes. Lymphocytes generate
immune responses against infecting agents, while monocytes are phagocytic in nature.
(3) Platelets : Platelets are small irregular bodies present in blood. They contain essential
chemicals that help in clotting. The main function of platelets is to promote clotting.

Q2 What is the importance of plasma proteins?

Answer. Plasma is the colourless uid of blood which helps in the transport of food, C02, waste
products, and salts. It constitutes about 55% of blood. About 6.8% of the plasma is constituted by
proteins such as brinogens, globulins, and albumins. Fibrinogen is a plasma glycoprotein
synthesised by the liver. It plays a role in the clotting of blood. Globulin is a major protein of the
plasma. It protects the body against infecting agents. Albumin is a major protein of the plasma. It
helps in maintaining the uid volume within the vascular space.

Q3

Answer.

Q4 Why do we consider blood as a connective tissue?

Answer. Connective tissues have cells scattered throughout an extra-cellular matrix. They connect
different body systems. Blood is considered as a type of connective tissue because of two reasons.
(i) Like the other connective tissues, blood is mesodermal in origin.
(ii) It connects the body systems, transports oxygen and nutrients to all the parts of the body, and
removes the waste products. Blood has an extra-cellular matrix called plasma, with red blood cells,
white blood cells, and platelets oating in it.

Q5 What is the difference between lymph and blood?

Answer.

Q6 What is meant by double circulation? What is its signi cance?

Answer. Double circulation is a process during which blood passes twice through the heart during
one complete cycle. This type of circulation is found in amphibians, reptiles, birds, and mammals.
However, it is more prominent in birds and mammals as in them the heart is completely divided
into four chambers — the right atrium, the right ventricle, the left atrium, and the left ventricle.

The movement of blood in an organism is divided into two parts:
(i) Systemic circulation
(ii) Pulmonary circulation

Systemic circulation involves the movement of oxygenated blood from the left ventricle of the
heart to the aorta. It is then carried by blood through a network of arteries, arterioles, and
capillaries to the tissues. From the tissues, the deoxygenated blood is collected by the venules,
veins, and vena cava, and is emptied into the left auricle.
Pulmonary circulation involves the movement of deoxygenated blood from the right ventricle to
the ulmon arte which then carries blood to the lungs for oxygenation. From the lungs, the
oxygenated blood is carried by the pulmonary veins into the left atrium. Hence, in double
circulation, blood has to pass alternately through the lungs and the tissues.
Signi cance of double circulation:
The separation of oxygenated and deoxygenated blood allows a more ef cient supply of oxygen to
the body cells. Blood is circulated to the body tissues through systemic circulation and to the
lungs through pulmonary circulation.

Q7 Write the differences between:
(a) Blood and Lymph
(b) Open and Closed system of circulation
(c) Systole and Diastole
(d) P-wave and T-wave

Answer. (a) Blood and Lymph

(b) Open and Closed system of circulation

(c) Systole and Diastole

(d) P-wave and T-wave

Q8 Describe the evolutionary change in the pattern of heart among the vertebrates.

Answer. Answer All vertebrates possess a heart — a hollow muscular organ composed of cardiac
muscle bres. The function of the heart is to pump oxygen to all parts of the body. The evolution
of the heart is based on the separation of oxygenated blood from deoxygenated blood for ef cient
oxygen transport.
In shes, the heart was like a hollow tube. This evolved into the four-chambered heart in
mammals.
Piscean heart Fish has only two chambers in its heart — one auricle and one ventricle. Since both
the auricle and the ventricle remain undivided, only deoxygenated blood passes through it. The
deoxygenated blood enters the gills for oxygenation from the ventricle. It has additional chambers
such as sinus venosus and conus arteriosus.

Amphibian heart
Amphibians, such as frogs, have three-chambered hearts, with two auricles and one ventricle. The

auricle is divided into a right and a left chamber by an inter-auricular septum, while the ventricle
remains undivided. Additional chambers such as sinus venosus and conus arteriosus are also
present. The oxygenated blood from the lungs enters the left auricle and simultaneously, the
deoxygenated blood from the body enters the right auricle. Both these auricles empty into the
ventricle, wherein the oxygenated and deoxygenated blood get mixed to some extent.

Reptilian heart
Reptiles have incomplete four-chambered hearts, except for crocodiles, alligators, and gharials.
They have only one accessory chamber called sinus venosus. The reptilian heart also shows mixed
blood circulation.

Avian and mammalian hearts
They have two pairs of chambers for separating oxygenated and deoxygenated bloods. The heart is
divided into four chambers. The upper two chambers are called atria and the lower two chambers
are called ventricles. The chambers are separated by a muscular wall that prevents the mixing of
the blood rich in oxygen with the blood rich in carbon dioxide.

Q9 Why do we call our heart myogenic?

Answer. In the human heart, contraction is initiated by a special modi ed heart muscle known as
sinoatrial node. It is located in the right atrium. The SA node has the inherent power of generating
a wave of contraction and controlling the heartbeat. Hence, it is known as the pacemaker. Since
the heartbeat is initiated by the SA node and the impulse of contraction originates in the heart
itself, the human heart is termed myogenic. The hearts of vertebrates and molluscs are also
myogenic.

Q10 Sino-atrial node is called the pacemaker of our heart. Why?

Answer. The sino-atrial (SA) node is a specialised bundle of neurons located in the upper part of
the right atrium of the heart. The cardiac impulse originating from the SA node triggers a
sequence of electrical events in the heart, thereby controlling the sequence of muscle contraction
that pumps blood out of the heart. Since the SA node initiates and maintains the rhythmicity of
the heart, it is known as the natural pacemaker of the human body.

Q11 What is the signi cance of atrio-ventricular node and atrio-ventricular bundle in the
functioning of heart?

Answer. The atrioventricular (AV) node is present in the right atrium, near the base of the inter-
auricular septum that separates the right auricle from the ventricle. It gives rise to the bundle of
His that conducts the cardiac impulses from the auricles to the ventricles. As the bundle of His
passes the ventricle along the inter-ventricular septum, it divides into two branches — the right
ventricle and the left ventricle.
The end branches of this conducting system then forms a network of Purkinje bres that penetrate
into the myocardium. The auricular contraction initiated by the wave of excitation from the sino-
atrial node (SA node) stimulates the atrio-ventricular node, thereby leading to the contraction of

ventricles through the bundle of His and Purkinje bres. Hence, the atrio-ventricular node and the
atrioventricular bundle play a role in the contraction of ventricles.

Q12 De ne a cardiac cycle and the cardiac output.

Answer. Cardiac cycle is de ned as the complete cycle of events in the heart from the beginning of
one heart beat to the beginning of the next. It comprises three stages — atrial systole, ventricular
systole, and complete cardiac diastole. Cardiac output is de ned as the amount of blood pumped
out by the ventricles in a minute.

Q13 Explain heart sounds.

Answer. Heart sounds are noises generated by the closing and opening of the heart valves. In a
healthy individual, there are two normal heart sounds called lub and dub. Lub is the rst heart
sound. It is associated with the closure of the tricuspid and bicuspid valves at the beginning of
systole. The second heart sound dub is associated with the closure of the semilunar valves at the
beginning of diastole. These sounds provide important information about the condition and
working of the heart.

Q14 Draw a standard ECG and explain the different segments in it.

Answer. Electrocardiogram is a graphical representation of the cardiac cycle produced by an
electrograph. The diagrammatic representation of a standard ECG is shown below.

A typical human electrocardiogram has ve waves — P, Q, R, S, and T. The P, R, and T-waves are
above the base line and are known as positive waves. The Q and S- waves are below the base line
and are known as negative waves. The P-wave is of atrial origin, while the Q, R, S, and T-waves are
of ventricular origin.
(a) The P-wave indicates atrial depolarisation. During this wave, the impulse of contraction is

generated by the SA node. The PQ-wave represents atrial contraction.
(b) The QR-wave is preceded by ventricular contraction. It represents the spread of the impulse of
contraction from the AV node to the wall of the ventricle. It leads to ventricular depolarisation.
(c) The RS-wave represents ventricular contraction of about 0.3 sec.
(d) The ST-wave represents ventricular relaxation of about 0.4 sec. During this phase, the
ventricles relax and return to their normal state.
(e) The T-wave represents ventricular relaxation.