NCERT Solutions for Class 11 Biology Chapter 18

NCERT Solutions for Class 11 Biology Chapter 18 by Extramarks are detailed and step-by-step solutions prepared by subject matter experts. Students can use these solutions to find accurate answers to the questions given at the end of NCERT Class 11 Biology Chapter 18.

To make the best use of these solutions, students should ideally go through the chapter at least once, attempt textbook questions on their own, and then cross verify using these resources. NCERT Solutions for Class 11 Biology Chapter 18 can also be very useful for last-minute preparations.

NCERT Solutions for Class 11 Biology Chapter 18 – Body Fluids and Circulation

Access NCERT Solutions for Class 11 Biology Chapter 18 – Body Fluids and Circulation 

NCERT Solutions for Class 11 Biology Body Fluids and Circulation 

In Biology Class 11 Chapter 18, students will learn about body fluids and their functions of circulating necessary nutrients and substances within the body. The chapter talks in detail about blood circulation, the different functions of blood, its composition, and the entire process of blood circulation inside the body including pulmonary and systemic circulatory pathways.

Students can access the NCERT Solutions for Class 11 Biology Body Fluids and Circulation here and prepare better for their examinations.

NCERT Solutions for Chapter 18 Class 11 Biology – Body Fluids and Circulation

Body Fluids and Circulation Chapter in NCERT Solutions for Chapter 18 Biology Class 11 falls under Unit V, Human Physiology. This particular chapter teaches students about the concepts related to blood circulation and the characteristics of tissue fluids (blood and lymph). Other major topics discussed in this chapter include double circulation, cardiac process regulation, pathways relating to circulation, disorders of cardiac activity, plasma, the entire human circulatory system, blood groups, ECG, and more.

Chapter 18 Biology Class 11 will teach students about the circulatory structural differences in the types of organisms, depending on the level of physical and mental complexity of the animal. The chapter also discusses the health of the heart, blood transfusions, number of blood particles; health and unhealthy habits that will affect the health of your heart. 

NCERT Solutions for Class 11 Chapter 18 – Marks Distribution

Chapter 18 Biology Class 11 NCERT Solutions comes under Unit 5 of the CBSE Class 11 Biology. The entire unit carries a total of 18 marks in the examinations. In the NEET exam, this chapter has a 20% topic weightage of the total grade. 

Students should know the topics covered in this chapter and master them. The main topics covered in this chapter are:

  • Blood
  • Plasma
  • Blood Groups
  • Element Formation
  • Blood Coagulation
  • Tissue Fluids 
  • The Circulatory system in Humans
  • The cardiac Cycle 
  • Electrocardiograph
  • Double Circulation
  • Disorders concerning Circulation
  • Cardiac activity and its Regulation

Benefits for NCERT Solutions for Class 11 Biology Chapter 18 – Body Fluids and Circulation

It is important for students to study the entire chapter and solve the questions not just for comprehensive learning, but also to do well in their exams. The benefits of including NCERT Solutions for Class 11 Biology Chapter 18 in one’s preparation are as follows:  

  • NCERT Solutions for Class 11 Biology Chapter 18 provide complete answers to all the textbook questions covered under Chapter 18.
  • The solutions are written in a simple language
  • Since these solutions are drafted by experts, students can use these to get an idea of how they should write their answers in final exams, how long or detailed the answers need to be, and what exactly an evaluator considers a good answer.

Related Questions 

  1. Mention the names of any eight common diseases, their causative agents, symptoms, and prevention measures. 
  2. Why do cancer cells lack contact inhibition?
  3. Are T cells innate or adaptive?
  4. Name one medical technique which is based on magnesium produced in the human body and for what purpose is this technique used?
  5. What is the difference between vaccines and medicines?
  6. Which is an example of anaerobic exercise?
  7. What are the symptoms of a weak heart?
  8. What is the first sign of hypoxia?
  9. Which one of the following is responsible for blue baby syndrome?
  1. Fluoride 
  2. Nitrate 
  3. Arsenic
  4. Lead

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


Erythrocytes, leucocytes and platelets are the formed elements of blood. They constitute approximately 45% of the blood.

Erythrocytes: Erythrocytes or red blood cells (RBCs) are essential for the transport of respiratory gases (oxygen and carbon dioxide) across the body.

Leucocytes: Leucocytes are essential for providing immunity against pathogens and other foreign substances.

  • Granulocytes: Neutrophils, eosinophils and basophils phagocytose infecting pathogens.
  • Agranulocytes: B lymphocytes and T lymphocytes are essential for both innate and acquired immunity.

Platelets: Platelets release the factors which are required for blood clotting.

Q.2 What is the importance of plasma proteins?


The proteins constitute 6-8% of plasma. Major proteins of plasma are fibrinogen, globulins and albumins. The function of these plasma proteins is as follows:

  • Fibrinogen is essential for blood clotting.
  • Globulins (immunoglobulins or antibodies) form the defence system of the body and prevent infections.
  • Albumins maintain the osmotic balance of the blood.
  • Plasma proteins also help in the transportation of lipids and hormones.

Q.3 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


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

Q.4 Why do we consider blood as a connective tissue?


Connective tissue supports and connects different types of tissues and organs of the body. Blood is considered as a connective tissue due to the following reasons:

a) It is mesodermal in origin like other connective tissues.

b) Like connective tissues, blood has plasma as the extracellular matrix in which various formed elements (cellular components) like erythrocytes, leucocytes and platelets are suspended.

c) It connects various body parts and organ systems. Nutrients, hormones, oxygen and other essential elements are transported from one part of the body to another through the blood. Blood also carries waste products from various organs to the site of excretion.

Q.5 What is the difference between lymph and blood?


Lymph Blood
Lymph is the component of the lymphatic system. Blood is part of the circulatory system.
Lymph is colourless due to the absence of red blood cells (RBCs). Blood is red due to the presence of haemoglobin containing RBCs.
Lymph contains plasma, a few number of WBCs (white blood cells) and platelets. Blood contains RBCs, WBCs and platelets.
It lacks proteins. Blood contains proteins like albumin, globulin and fibrinogen.
It is the part of the immune system and plays a major role in defense mechanism. It circulates oxygen, carbon dioxide, hormones, nutrients, and metabolic waste products in the body.

Q.6 What is meant by double circulation? What is its significance?


Double circulation refers to the process wherein blood passes two times through the heart in one complete cycle. In this circulation, the blood circulates in two distinct and separate pathways/loops (pulmonary circulation and systemic circulation). It is observed in birds and mammals as they have a four-chambered heart.

Pulmonary circulation: The pumping of blood from the heart to the lungs forms the pulmonary circuit. The right atrium of the heart receives deoxygenated blood from all the body parts. The deoxygenated blood then moves to the right ventricle. This deoxygenated blood is carried to the lungs from the right ventricle of the heart via the pulmonary artery. The blood is oxygenated in the lungs and is transported back to the left atrium by the pulmonary vein.

Systemic circulation: Flow of oxygenated blood, from the left ventricle of the heart, via arteries, arterioles and capillaries to the tissues is known as a systemic circuit. In the lungs, deoxygenated blood acquires oxygen and goes into the left atrium of the heart. From the left atrium, the oxygenated blood goes to left ventricle. Thereafter, the blood moves into the aorta and is carried to different body tissues by a network of arterioles, arteries, and capillaries. The deoxygenated blood is then collected from body tissues by a system of venules, veins and vena cava and emptied into the right atrium. This forms the systemic circulation. Systemic circulation provides nutrients, oxygen and other necessary substances to various body parts and carries back carbon dioxide and other harmful waste products away for elimination from the body.

Significance: The importance of double circulation is that it does not allow the mixing of oxygenated and deoxygenated blood. Thus, it ensures the efficient oxygen supply to the body organs.

Q.7 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) Blood and Lymph

Blood Lymph
Blood is red due to the presence of haemoglobin in red blood cells (RBCs). Lymph is colourless due to the absence of red blood cells (RBCs).
Blood contains RBCs, WBCs and platelets. Lymph contains less number of WBCs and platelets.
Blood contains proteins. It lacks proteins.
It transports digested food materials, respiratory gases and metabolic waste products. It transports digested fats and fat-soluble vitamins. and is involved in the defence mechanism.
The flow of blood in the vessels is fast. Lymph flows slowly.

(b) Open and Closed system of circulation

Closed system Open system
In the closed type of circulatory system, blood flows inside the blood vessels all the time. In the open type of circulatory system, blood is directly pumped into the body cavity called sinuses.
There are valves to prevent backward flow of blood. There are no valves to prevent backward flow of blood.
Oxygen and nutrients diffuse out from the blood vessels to nourish the surrounding tissues/organs. Oxygen and nutrients are directly supplied to tissues/organs by the blood present in the body cavity.
Blood and interstitial fluids do not mix. There is no distinction between blood and interstitial fluid. They are called as hemolymph.
Blood flows at relatively higher speed. Blood (hemolymph) flows at very slow speed.
Closed system is present in annelids and chordates. Open type circulatory system is present in molluscs and arthropods.

(c) Systole and Diastole

Systole Diastole
Systole refers to the contraction of heart muscles. Diastole refers to the relaxation of heart muscles.
During systole, blood is pumped into the aorta and pulmonary arteries. Right ventricle contracts to send blood to the lungs via pulmonary artery. Left ventricle pumps blood into aorta. During diastole, the heart chambers come back to original size to receive the blood. Blood received by atria is released into ventricles.
Atrio-ventricular valves close and semilunar valves open. Atrio-ventricular valves open and semilunar valves close to prevent backflow of blood into the atria.

(d) P-wave and T-wave

P-wave T-wave
It indicates activation of Sino-atrial node. It indicates ventricular relaxation.
P-wave represents atrial excitation (depolarization) that results in atrial contraction. T-wave shows the return of ventricles from excited to normal state (repolarization).

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


The heart is a hollow muscular organ that pumps blood to all the tissues of the body. This process provides oxygen to various body parts. Evolution of heart has helped in more efficient transport of oxygen in the body by preventing the mixing of oxygenated and deoxygenated blood as described below:

  • Fish: Fish have a very simple heart structure. Its heart is a two-chambered hollow tube-like structure. It has one atrium and one ventricle. Deoxygenated blood enters the atrium of the heart from where the blood is pumped into the ventricle. It then enters into the gills for oxygenation. The blood oxygenated in the gills is circulated across the body and finally, the deoxygenated blood from different body parts is transported back into the atrium of the heart.
  • Amphibians: Amphibians have a three-chambered heart: two auricles and one ventricle. Oxygenated blood from the lungs enters into the left auricle while deoxygenated blood from other body parts enters into the right auricle. Both auricles transfer blood to the ventricle. In the ventricles, the oxygenated and deoxygenated blood mixes and this mixed blood is circulated to different body parts.
  • Reptiles: Reptilians (except crocodiles) have an incomplete four-chambered heart. They have two auricles and a ventricle which is partially divided into two chambers. There is partial mixing of oxygenated and deoxygenated blood due to incomplete partitioning of the ventricles.
  • Mammals and birds: Mammals and birds have a four-chambered heart. This prevents the mixing of oxygenated and deoxygenated blood. Right atrium receives deoxygenated blood and transfers it into right ventricle. From the right ventricle, deoxygenated blood is pumped into lungs to get oxygenated. Oxygenated blood is returned to left auricle of the heart. From left auricle, the oxygenated blood flows into the left ventricle and is pumped to whole body.

Q.9 Why do we call our heart myogenic?


Our heart is called myogenic heart because it receives signals for contraction from specialized cells called cardiac myocytes found in it. Cardiac myocytes form a specialized structure, known as nodal tissue, that possesses both muscular and nervous characteristics. The human heart receives the signals for contraction from the nodal tissue.

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


Sino-atrial node is called the pacemaker of heart because it is a specialized structure made up of cardiac myocytes that have both muscular and nervous characteristics. It is located in the upper side of right atrium. This structure has the ability to generate action potentials without any external stimuli. It initiates the impulse of contraction that subsequently spreads throughout the heart. It can generate a maximum of 70-75 action potentials per minute. It initiates and maintains rhythmic contraction of heart. Our heart usually beats around 70-75 times in a minute.

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


Atrio-ventricular (AV) node is present in right auricle at the base of inter-auricular septum, which separates right auricle from the ventricle. From this node, a bundle of nodal fibres called AV bundle arises and it passes via the AV septa. Immediately, it divides into left and right bundle. These bundles give rise to Purkinje fibres, which penetrate into the myocardium. These fibres along with the bundles form the structure called the bundle of His. This nodal system is auto-excitable, that is, it possesses the ability to generate an action potential in the absence of electric impulse. The electrical impulse is then passed on to ventricle by the bundle of His and Purkinje fibres. This impulse leads to contraction of the ventricles.

Q.12 Define a cardiac cycle and the cardiac output.


A complete cycle refers to the complete cycle of events from the start of one heartbeat to the start of next. It includes diastole and systole that involves filling of the heart with blood and then pumping it out. During diastole, the heart relaxes and fills with the blood. During systole, the ventricle contracts and pumps out the blood.

Cardiac output is the amount of blood pumped out by each ventricle in a minute. It is calculated by multiplying stroke volume (volume of blood pumped by each ventricle in a cardiac cycle) and heart rate (beats per minute).

Q.13 Explain heart sounds.


When the valves of heart open and close during the cardiac cycle, they produce a sound known as heart sound. These sounds are lub and dub. Lub is the first sound and is produced by the vibrations of the heart when bicuspid and tricuspid valves (valves present between atria and ventricle) close at the beginning of systole (when ventricular muscles contract). It is followed by second sound dub which is produced by vibrations caused due to closing of semilunar valves (which guard the pulmonary artery and the aorta) at the end of the systole.

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


Electrocardiogram (ECG) is the graphical representation of the cardiac cycle. It is produced by an electrocardiograph. The normal ECG indicating that the heart is functioning properly is shown below.

A typical human ECG includes the following waves:

• P-wave: It represents depolarization of the right and left atria. The impulse of contraction by the SA node is generated during this wave.

• QRS wave: It shows depolarization and contraction of the right and left ventricles. The contraction starts shortly after Q and indicates the beginning of systole.

• T-wave: It represents repolarization (return from excited to normal) and relaxation of the ventricles. Its end indicates the end of systole.

Waves P, R and T are above the base line and are called positive waves, while Q and S are below the base line and are known as negative waves.

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FAQs (Frequently Asked Questions)

1. What is the significance of plasma proteins?

Plasma proteins include Globulins, Albumins, and Fibrinogens. Globulins that assist in the defence mechanism in the body are called immunoglobulins. The osmotic balance of the body is maintained by albumin. Fibrinogens help to maintain blood coagulation.

2. What is the function of erythrocytes?

Erythrocytes are also known as red blood cells (RBCs). They carry oxygen and haemoglobin throughout the body. The haemoglobin reacts with oxygen and forms oxyhaemoglobin. 

3. Explain the function of Leukocytes and Thrombocytes.

Leukocytes are the white blood cells that kill germs. Neutrophils act as a defence mechanism for the bacteria called phagocytosis. Thrombocytes help in the coagulation of blood. 

4. What are the important topics of NCERT Solutions for Class 11 Biology Chapter 18 Body Fluids and Circulation?

The important topics of NCERT Solutions for Class 11 Biology Chapter 18 – Body fluids and Circulation are:

  • Components and elements in the blood
  • Plasma proteins
  • Blood as connective tissue
  • The difference between lymph and the blood, open and closed system of circulation
  • Systole and Diastole
  • P-wave
  • T-wave and cardiac cycle
  • Atrioventricular node
  • Atrial-lenticular bundle

5. What are the benefits of solutions for NCERT Class 11 Biology Chapter 18 Body Fluids and Circulation?

There are numerous advantages to using NCERT Class 11 Biology Chapter 18 – Fluids and circulation. The questions and answers given are clear and precise. All of the answers follow a systematic method of answering the question. Students can follow the same and work on their answers to provide concise, relevant, and well-structured content. Extramarks’ subject experts adhere to CBSE guidelines, ensuring that these solutions are accurate and reliable.

6. “Blood is considered to be a connective tissue” Explain.

Blood is known to be a connective tissue as it is mesodermally inferred and contains an extra cell lattice known as plasma. It is abundant and widely dispersed throughout the body. Connective tissues can provide specific connections and ties between different organs, assisting different organs of the body and subsequently moving oxygen and other supplements inside the body, removing waste from the body, and flowing throughout the body. Henceforth, it is called connective tissue. 

7. Why is the human heart known to be Myogenic?

Contraction of the heart happens due to a uniquely adjusted heart muscle known as the sinoatrial node which is situated in the right atrium. The characteristic feature of this node is in producing a rush of compression and controlling the heartbeat. Hence, it is known as the pacemaker. Since the heartbeat is started by the SA node and the motivation to withdraw begins in the heart itself, the human heart is known to be myogenic. The hearts of vertebrates and molluscs are also myogenic. 

8. What is meant by double circulation and what is its significance?

It is the process in which blood passes through the heart twice in one complete cycle. The process involves two types of blood circulations;

  1. Systemic circulation – In this circulation, the flow of the oxygenated blood takes place from the left ventricle of the heart to the aorta. Then a network of arteries, arterioles, and capillaries supply this oxygenated blood to the various tissues in the body. From the tissues, the deoxygenated blood is carried by the veins, venules, and vena cava, and is emptied in the right atrium.
  2. Pulmonary Circulation – This circulation is the flow of the deoxygenated blood from the right ventricle to the pulmonary artery, which then carries the blood to the lungs to get oxygenated. Then the oxygenated blood from the lungs is carried by the pulmonary veins to the left atrium.  

The significance of double circulation is that complete separation of oxygenated and deoxygenated blood takes place which allows a more efficient supply of oxygen to the cells in the body.