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NCERT Solutions Class 11 Biology Chapter 15 Body Fluids and Circulation

Last Updated : 15 May, 2023
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NCERT Solutions for class 11 Chapter-15  Body Fluids and Circulation. The chapter on  Body Fluids and Circulation is important for students approaching the board exams. This article introduces NCERT solutions designed to help students. It explains the concepts of further learning and how to write to get good grades in exams. The solutions are presented in elementary language for ease of understanding.

NCERT CBSE Chapter 15 Body Fluids and Circulation discusses the importance of fluids for the body and how they are circulated. All living cells need oxygen, nutrition, and a few other fundamental components to function correctly. Additionally, regular elimination of waste or toxic substances from the body is necessary for the healthy operation of the bodily tissues. The bodily fluid that is most frequently used in higher organisms, including humans is blood. Lymph is another often-used bodily fluid that aids in the transportation of vital creatine components. This whole chapter talks in detail about Body fluids and how it actually circulates Revise the basic concepts of Body Fluids and Circulation for quick revision and class notes.

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


Blood corpuscles are the formed elements in the blood, constituting 45% of our body’s whole blood. Erythrocytes (RBCs or red blood corpuscles), leucocytes (WBCs or white blood corpuscles) and thrombocytes or blood platelets are formed elements in the blood.

  • Erythrocytes: These are the red blood cells that are most prevalent and contain haemoglobin which is the red pigment that gives them their characteristic red colour. All areas of the body receive oxygen because of erythrocytes. These are constantly created in some body regions, such as the marrow of long bones and ribs. Per cubic millimetre of blood, there are roughly 4–6 million RBCs.
  • Leukocytes: These are colourless cells that lack haemoglobin. They are classified into two groups.
    • Granulocytes: These leukocytes include granules in their cytoplasm and include neutrophils, eosinophils, and basophils. Neutrophils, phagocytic cells, defend the body against several infectious pathogens. Eosinophils are responsible for allergic reactions, whereas basophils are responsible for inflammatory responses.
    • Agranulocytes: Lymphocytes and monocytes are examples of agranulocytes. Lymphocytes produce immunological responses against invading agents, whereas monocytes are phagocytic.
  • Platelets are little irregular entities found in the blood. They include important molecules that aid in coagulation. Platelets’ primary purpose is to facilitate coagulation.

Q2: What is the importance of plasma proteins?


Plasma is the colourless fluid that makes up approximately 55% of blood. It assists in transporting food, CO2, waste products, salts, and other items. Proteins such as fibrinogens, globulins, and albumins make up around 6.8% of plasma. Fibrinogen is a plasma glycoprotein that the liver produces. It is involved in blood clotting. Globulin is a key protein found in plasma that protects the body from invading pathogens. Albumin is a plasma protein that regulates fluid volume inside the vascular region.

Q3: Match Column I with Column II:

Column I Column II
(a) Eosinophils (i) Coagulation
(b) RBC (ii) Universal Recipient
(c) AB Group (iii) Resist Infections
(d) Platelets (iv) Contraction of Heart
(e) Systole (v) Gas transport


The correct match is – a-iii, b-v, c-ii, d-i, e-iv

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

Q4: Why do we consider blood as a connective tissue? 


Blood is regarded as connective tissue for the following reasons:

  1. Connective tissues bind, connect, or support the body’s other organs. They are the most abundant and extensively distributed tissue in the body. Extracellular matrix and live cells make up connective tissue. Blood is a mobile tissue that is made up of free cells and fluid matrix and is a type of vascular connective tissue.
  2. Blood transfers gases, nutrients, and hormones from one organ to another in the body which circulates throughout the body maintaining connectivity.
  3. Similar to other connective tissues, blood is mesodermal in origin.

As a result, blood is categorised as connective tissue.

Q5: What is the difference between lymph and blood?




Blood is the connective tissue that is red and is in liquid. Lymph is a viscous fluid with no colour.
It passes through arteries, veins, and capillaries, which are blood vessels It circulates through lymphatic vessels.
Haemoglobin, red blood cells, white blood cells, and platelets are also present It also has lymphocytes, which are white blood cells
It moves gases and other nutrients throughout the body. The lymph facilitates the exchange of nutrients and gases between the blood and cells.
More calcium, phosphorus and protein are present in its plasma. Less protein, calcium and phosphorus are present in its plasma

Q6: What is meant by double circulation? What is its significance?


Blood circulates twice through the heart during a single full cycle, which is known as double circulation. Amphibians, reptiles, birds, and mammals all have this sort of circulation. However, it is more noticeable in birds and mammals since their hearts are entirely divided into four chambers: the right atrium, right ventricle, left atrium, and left ventricle. In an organism, there are two distinct phases to the blood’s movement:

  1. Systemic circulation 
  2. Pulmonary circulation.

The transfer of oxygenated blood from the left ventricle of the heart to the aorta is referred to as systemic circulation. The blood then transports it to the tissues via a system of capillaries, arteries, and arterioles. The venules, veins, and vena cava draw deoxygenated blood from the tissues and release it into the left auricle.

Deoxygenated blood is sent from the right ventricle to the pulmonary artery, which subsequently transports blood to the lungs for oxygenation, as part of the pulmonary circulation.


  • Double circulation has important health benefits since it provides a more effective supply of oxygen to the body’s cells. 
  • The circulation method used here monitors and stops the mixing of oxygenated and deoxygenated blood as pulmonary circulation carries blood to the lungs, and systemic circulation carries blood to the body’s tissues.

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


(a) Difference Between Blood and Lymph



Blood is the connective tissue that is red and is in liquid. Lymph is a viscous fluid with no colour.
It passes through arteries, veins, and capillaries, which are blood vessels It circulates through lymphatic vessels.
Haemoglobin, red blood cells, white blood cells, and platelets are also present It also has lymphocytes, which are white blood cells
It moves gases and other nutrients throughout the body. The lymph facilitates the exchange of nutrients and gases between the blood and cells.
More calcium, phosphorus and protein are present in its plasma. Less protein, calcium and phosphorus are present in its plasma

(b) Difference Between Open and Closed system of Circulation

Open Circulatory system

Closed Circulatory system

The heart pumps blood through major veins into bodily cavities known as sinuses in this system. Blood is pumped through a closed system of vessels by the heart in this system.
Blood comes in contact with the body tissues right away.. Blood indirectly comes into contact with body tissues. Low pressure causes blood to flow.
Low pressure causes blood to flow. The high pressure causes blood to flow.
There is no way to control blood flow. It’s possible to control blood flow.
In arthropods and molluscs, this is present. Vertebrates, echinoderms, and annelids all exhibit this.

(c) Difference Between Systole and Diastole



It is caused by heart chamber contraction. It refers to the relaxation of the heart chambers.
Systole is the time when blood is pumped from the chambers. During diastole, blood enters the chambers.
The heart’s internal blood pressure rises as a result. Heart blood pressure decreases as a result.

(d) Difference Between P-wave and T-wave


T- wave

An ECG’s first wave, the “P” wave, is a positive wave. It denotes that the SA nodes are active. The final wave in an ECG, the “T” wave, is also a positive wave. It stands for relaxation of the ventricles.
The P-wave typically lasts for 0.1 seconds. The T-wave typically lasts for 0.2 seconds.
The atrial complex is another name for the p wave. The Ventricular Complex is yet another name for it.
Due to the atrial musculature’s depolarization, a P-wave is generated. When the ventricular muscle repolarizes, a T-wave results.
P-waves typically have an amplitude between 0.1 and 0.12 mV. T-waves typically have an amplitude of 0.3 mV.

Q8. Describe the Evolutionary Change in the Pattern of the Heart among the Vertebrates.


The following points mentioned below indicate evolutionary changes in vertebrate heart patterns:

  • From a fish’s two-chambered heart to mammals’ and birds’ four-chambered hearts, the vertebrate heart has undergone an evolution.
  • The fish has a two-chambered heart. Blood that has been deoxygenated by the heart is pumped to the gills, where it is oxygenated and delivered to the body. The heart receives deoxygenated blood.
  • The left atrium, right atrium, and ventricle are the three chambers found in amphibians.
  • In Amphibians, the epidermis, the lungs, or the gills provide the left atrium with oxygenated blood. Deoxygenated blood from the bodily organs is delivered to the right atrium. But finally, the ventricle mixes the two types of blood, and the combined blood is delivered to the body.
  • When it comes to reptiles, the ventricle is only partially divided by a septum. Here, the blood is not mixed with deoxygenated blood.
  • In mammals, birds, and crocodiles, the heart is entirely divided into two ventricles and two atria, which maintain the separation of oxygenated and deoxygenated blood.
  • From fish to mammals, the heart has undergone structural changes that guarantee the body’s supply of oxygen-rich blood. The four-chambered design ensures that the blood flow is controlled at the same time.

 Q9: Why do we call our Heart Myogenic?


”Mayo means “muscle,” and genic means “originating from.” We refer to the cardiac impulse as myogenic since it originates in the heart muscles.  It indicates that a patch of the modified heart muscle known as the sino-atrial node, also known as the pacemaker, starts the heart’s own beat. This node is located in the wall of the right atrium, close to the superior vena cava’s opening. Mollusks and other vertebrates, including humans, have myogenic hearts.

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


The sino-atrial node is referred to as the pacemaker of the heart since it has the ability to generate a cardiac impulse. The action potential and cardiac impulse are both produced by the sino-atrial node. The atria and ventricles are then affected by this cardiac impulse, which causes them to contract or relax. The SA node can produce up to 70–75 action potentials per minute at its maximal pace. It also regulates the heart’s rhythmic contractile action.

Q11: What is the significance of the atrioventricular node and atrioventricular bundle in the functioning of the heart? 


A mass of neuromuscular tissue called the atrioventricular node (AVN) is located in the right atrium’s wall, close to the interatrial septum’s base. Since it sends the impulses started by the SA node to all areas of the ventricles, the AV node serves as the heart’s pacemaker.

The atrioventricular node and atrioventricular bundle are important for the proper operation of the heart because

  • The cardiac impulse is received by the atrioventricular node from the SA node.
  • The cardiac impulse is carried farther toward the walls of the ventricles by the atrioventricular bundle, which emerges from the AV node.

Q12: Define the Cardiac Cycle and the Cardiac Output. 


Cardiac Cycle: 

  • The term “cardiac cycle” refers to the sequence of events that take place throughout a heartbeat, and one cardiac cycle lasts 0.8 seconds.The circulation of blood in the heart happens because of the alternating contraction and relaxation of the heart chambers 
  • The contraction is known as systole, while relaxation is known as diastole. 
  • Each phase of contraction (systole) is followed by a phase of relaxation or expansion (diastole).

Cardiac output:

  • It is the total volume of blood pumped out of each ventricle each minute.
  • Cardiac output is calculated as follows: stroke volume * beats per minute.
  • A typical person’s heart beats 72 times per minute, pumping out around 70 mL of blood with each beat. As a result, the average cardiac output is 5000 mL or 5 litres.

Q13: Explain Heart Sounds. 


Heart valves close and open, producing sounds that are known as heart sounds. Two typical heart sounds named lub and dub can be heard in a healthy person. During each cardiac cycle, lub and dubb are audible. The bicuspid and tricuspid valves closing together cause the first sound or lub. It has a low pitch. The closure of semilunar valves results in the second sound dub. It has a high pitch. In the clinical diagnosis of any heart-related illness, both sounds are crucial.

Q14: Draw a Standard ECG and explain the Different Segments in it.


An ECG shows the heart’s actions during a cardiac cycle graphically. Electrocardiograph, or ECG. Assume a patient is attached to the device with three electrical leads—one to each wrist and the left ankle—so that it can continually track the heartbeat of the patient. Multiple leads are placed in the chest area to provide a thorough assessment of the heart’s function.

  • A letter, ranging from P to T, designates each peak in the ECG and denotes a particular electrical activity of the heart.
  • P-wave: It symbolizes the atria’s electrical stimulation (or depolarization), which causes both atria to constrict.
  • QRS compound: It symbolizes the ventricles’ depolarization, which starts the contraction of the ventricles. The contraction begins shortly after the T-wave.
  • T-wave: It signifies the repolarization of the ventricles, which is the transition from an excited to a normal condition.

Systole ends when the T-wave reaches its peak. Counting the amount of QRS complexes that occur in a particular period clearly allows one to calculate an individual’s cardiac rate. Any divergence from this form denotes a potential illness or disease since the ECGs acquired from various individuals have essentially the same shape for a particular lead arrangement. It has significant clinical implications as a result.

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