Important Questions for CBSE Class 11 Biology Chapter 18 – Body Fluids and Circulation

Class 11 Biology Chapter 18 Important Questions: Body Fluids and Circulation

Science becomes more exciting when you get a grip on logical concepts. Biology is challenging and requires a  clear understanding of concepts, unlike a few other subjects, where you can memorise the formula and solve the question. Biology is a very vast subject which is subdivided into Botany and Zoology. Some students find Botany challenging, while others find Zoology comparatively easier. 

Class 11 Biology Chapter 18 is about Body Fluids and Circulation. The chapter revolves around blood, heart, arteries and veins. The topic is very lengthy, complicated and interconnected with each other.

Extramarks is the most trusted learning platform helping students to get a tight grip over complex subjects like Mathematics, Biology, Physics and Chemistry. Our study material Class 11 Biology chapter notes are valuable as they form the basis for the board and competitive exams. Students gain a lot of practical knowledge about the human body. 

Along with it students will find our question bank of Important Questions Class 11 Biology Chapter 18  to be very helpful. The solutions are prepared by our Science expert faculty members. The step-by-step answers given in our Biology Class 11  Chapter 18 Important Questions ensures to clear all the doubts and difficulties students often face while solving Biology questions. Students can register on Extramarks’ website to get access to our question bank of Class 11 Biology Chapter 18 Important Questions.

The student-friendly notes are designed according to the latest NCERT syllabus and pattern. Questions of Important Questions Class 11 Biology Chapter 18 are collated from various sources such as NCERT textbook, NCERT exemplar, past question papers, and other reference books.

Get Access to CBSE Class 11 Biology Chapter 18 Important Questions & Answers for the Academic Year 2022-23.

Class 11 Biology Chapter-wise important questions are available for free to students, and these questions are perfect for self-study.

Check out CBSE Class 11 Biology Important Questions for other chapters as well:

CBSE Class 11 Biology Important Questions

Sr No. Chapters Chapters Name
1 Chapter 1 The Living World
2 Chapter 2 Biological Classification
3 Chapter 3 Plant Kingdom
4 Chapter 4 Animal Kingdom
5 Chapter 5 Morphology of Flowering Plants
6 Chapter 6 Anatomy of Flowering Plants
7 Chapter 7 Structural Organisation in Animals
8 Chapter 8 Cell the Unit of Life
9 Chapter 9 Biomolecules
10 Chapter 10 Cell Cycle and Cell Division
11 Chapter 11 Transport in Plants
12 Chapter 12 Mineral Nutrition
13 Chapter 13 Photosynthesis in Higher Plants
14 Chapter 14 Respiration in Plants
15 Chapter 15 Plant Growth and Development
16 Chapter 16 Digestion and Absorption
17 Chapter 17 Breathing and Exchange of Gases
18 Chapter 18 Body Fluids and Circulation
19 Chapter 19 Excretory Products and their Elimination
20 Chapter 20 Locomotion and Movement
21 Chapter 21 Neural Control and Coordination
22 Chapter 22 Chemical Coordination and Integration

Body Fluids and Circulation Class 11 Important Questions

The Extramarks question bank for Important Questions Biology Class 11 Chapter 18 is a well-planned exam-oriented solution for students. The answers are bound to benefit students in ample ways as it covers a variety of questions such as long and short questions, fill-in-the-blanks and multiple choice questions.

Given below are a few questions and their answers taken from our Important Questions Class 11 Biology Chapter 14. 

Question 1. Answer the following

  1. Name the major site where RBCs are formed.
  2. Which part of the heart is responsible for initiating and maintaining its rhythmic activity?
  3. What is specific in the heart of crocodiles among reptilians?

Answer 1:

  • Bone marrow is the primary site where RBCs are formed.
  • For initiating and maintaining the heart’s rhythmic activity, Sinoatrial Node (SA) is responsible.
  • All reptiles have three-chambered hearts, but the crocodile has a four-chambered heart.

Question 2. What physiological circumstances are responsible for erythroblastosis foetalis?

Answer 2: About 80-85 % of humans have Rh-antigen present on the surface of the erythrocytes. Rh-positive individuals possess the antigen, and Rh_ individuals do not have this antigen. When a person is exposed to Rh+ blood, anti-Rh antibodies are developed.

If Rh-negative pregnant woman bears an Rh-positive foetus, anti-Rh antibodies are formed during the first delivery when foetal blood comes in contact with the mother’s blood. If the woman carries a second foetus, Rh +, then anti-Rh antibodies in her blood enter the foetal circulation and cause damage to the RBC of the foetus. This is a fatal condition and is known as erythroblastosis foetalis.

Question 3. What is the significance of the hepatic portal system in the circulatory system?

Answer 3. A unique vascular system is present between the gut and liver. This is called the hepatic portal system. This system begins in the alimentary canal and ends in the liver. The hepatic portal vein carries blood from the intestine to the liver before it enters the blood. The liver has first access to nutrients after the digestion of food. In other words, we can say that digestive end products are brought to the liver before they are released in the modified form into the blood.

In humans, the blood supply to the liver is 1500 ml per minute. Out of this, 1000 ml comes from the hepatic portal vein, and 500 ml comes from the hepatic artery.

Question 4. Given below are the abnormal conditions related to blood circulation. Name the disorders.

  • Acute chest pain due to failure of oxygen supply to heart muscles.
  • Increased systolic pressure.

Answer 4. 

  • Angina. Due to the narrowing of the coronary artery, the blood supply to the heart muscles is reduced.
  • High blood pressure.

Question 5. Write the differences between blood and lymph.

Answer 5:

                                    BLOOD                       LYMPH
It is red because of the presence of haemoglobin in red cells. The Lymph is colourless due to the absence of red cells.
The composition of blood is plasma, RBC, WBC and platelets. The composition of lymph is plasma and WBC in low numbers.
The concentration of glucose is low. The glucose concentration is high compared to blood.
Blood clotting is fast. Lymph clotting is slow.
Blood carries material from one organ to the other. Lymph transports material from the tissue into the blood.
Blood flow is fast Lymph flow is very slow.
The Plasma of blood has more proteins, calcium and phosphorus. The Plasma of lymph has fewer proteins, calcium and phosphorus.
It moves away from the heart and towards the heart. It moves only in one direction from tissues to the subclavian.

Question 6. Thrombocytes are essential for the coagulation of blood. Explain.

Answer 6. Thrombocytes are necessary for the clotting of blood. It involves the following steps:

  • Platelets release thromboplastin, which is vital in clotting.
  • The primary factors responsible for clotting are fibrinogen, prothrombin, thromboplastin and calcium ions.


  • Thromboplastin help in the formation of prothrombinase, which inactivates heparin. There is the conversion of prothrombin into its active form called thrombin.
  • Thrombin is the proteolytic enzyme that converts fibrinogen to fibrin which is the insoluble form. These fibrin monomers polymerise to form long, sticky fibres.
  • The fibrin threads form a network in which dead and damaged formed elements of blood are trapped.
  • The clot is formed over the injured surface. It is reddish brown.
  • The serum is a straw-coloured fluid which separates from the clot.
  • The serum does not have fibrinogen, so it cannot clot.
  • Applied: The increase in the number of platelets is known as thrombocytosis, while a decrease is known as thrombocytopenic purpura.

Question 7. State the functions of the following in blood.

  • Fibrinogen
  • Globulin
  • Neutrophils
  • Lymphocytes

Answer 7:

  1. Fibrinogen is about 0.3 % in plasma and plays an essential role in blood clot formation at the site of injury.
  2. Globulin is of three types: α,β and . It constitutes 2 to 3 % of plasma proteins. The gamma globulins help in the formation of antibodies. The globulins are primarily involved in immunity and play an important role in the body’s defence mechanism by fighting infections.
  3. Neutrophils are phagocytic cells that destroy foreign organisms entering the body.
  4. Lymphocytes are of two types: T cells and B cells. They synthesise antibodies and play the primary role of providing immunity to the body.

Question 8. What is the importance of plasma proteins?

Answer 8. Plasma contains 7-8 % of proteins. They are albumin, globulin and fibrinogen. Albumin Is the maximum protein and helps in maintaining colloidal osmotic pressure.Globulins aid antibody formation and fibrinogen in blood clotting.

Question 9. Name the components of the formed elements in the blood and mention one major function of each.

Answer 9. The formed elements of blood are erythrocytes, leucocytes and platelets.

  • Erythrocytes or RBCs contain haemoglobin which carries oxygen. 
  • Leucocytes or WBC contain granulocytes and agranulocytes. B lymphocytes synthesise antibodies, neutrophils and monocytes involved in phagocytosis, acidophils produce antitoxin against the allergen, and basophils produce heparin and histamine.
  • Platelets are involved in blood clotting.

Question 10. Briefly describe the following:

  • Anaemia
  • Angina pectoris
  • Atherosclerosis
  • Hypertension
  • Heart failure

Answer 10:

  • Anaemia is the decrease in the amount of haemoglobin. Various types of anaemia are:

Nutritional anaemia is due to iron deficiency in the blood. 

Vitamin B12 and folic acid deficiency cause megaloblastic anaemia.

Pernicious anaemia is due to the deficiency of B12. In this type of anaemia, neurons disturb the myelin sheath formation of neurons. Also, it is fatal.

Sickle cell anaemia is a hereditary autosomal recessive disorder. The anaemia is characterised by the presence of sickle haemoglobin in which RBC are sickle-shaped. The RBCs are not capable of carrying enough oxygen to the tissues.

Thalassaemia is an autosomal recessive disorder. In which either the alpha or beta chain of haemoglobin is not synthesised.

  • Angina pectoris can occur in men and women of any age but is more common in early and middle-aged individuals. In this, enough oxygen does not reach the heart muscles. Due to the affected blood flow, the individual experiences acute chest pain. No problem is encountered during routine work, but pain may develop due to exertion or exercise.
  • Atherosclerosis is the disorder of arteries or blood vessels due to the deposition of calcium, cholesterol and fibrous tissue. This makes the lumen of arteries narrower. There is hardening of arteries and arterioles and loss of elasticity. The condition is also known as coronary artery disease and mainly affects those vessels which supply blood to the heart muscle.
  • High blood pressure is called hypertension. The pressure exerted by blood flow on the elastic walls of arteries is known as blood pressure. The usual range of blood pressure is 120/80 mm Hg. 120 mm Hg is the systolic pressure or pumping pressure. 80 mm Hg is the diastolic pressure or resting pressure. When this range is higher and above 140/90 mm Hg, it is called Hypertension. The condition affects vital organs of the body like the heart, brain and kidney.
  • Heart failure is when the heart fails to pump blood effectively to meet the body’s requirements. Since it causes congestion of the lungs, so the condition is also known as congestive heart failure.

Question 11. Explain the functional significance of the lymphatic system.

Answer 11: The lymphatic system contains: lymph, lymphatic capillaries, lymphatic vessels, lymphatic ducts and lymphatic nodes. Lymph is a fluid inside lymph vessels.

The Lymphatic system has the following significance:

  • To remove metabolic waste from the tissue
  • To carry nutrients, hormones, etc.
  • Absorption of fats via lacteals.
  • Renewal of Extracellular Fluid (ECF)
  • Maturation of lymphocytes.
  • Phagocytosis 

Question 12. Describe the following terms and give their location.

  • Bundle of His
  • Purkinje fibre

Answer 12:

  • The atrioventricular node is present close to the Tricuspid valve. From this AV node, a bundle of specialised muscle fibre arises, which is known as a Bundle of His or Atrio-ventricular bundles. They run in the anterior part of the interventricular septum and then bifurcate.
  • The atrioventricular bundle gives rise to minute fibres called Purkinje fibre. These are myocardial in origin and conduct impulses to all the portions of the walls of the ventricles.
  •  Purkinje fibre.

Question 13. Differentiate between the tricuspid and bicuspid valves.

Answer 13: Tricuspid valve comprises three muscular flaps and guards the opening between the right atrium and the right ventricle.

The bicuspid valve is also called the mitral valve. It guards the opening between the left atrium and left ventricle. It is associated with oxygenated blood.

Question 14. Distinguish between open and closed circulatory systems.

Answer 14:

Blood is in direct contact with tissue. Blood is not in direct contact with tissue.
Blood is filled in sinuses.  Blood does not come out of the vessel.
A large blood cavity called Haemocoel is present. Haemocoel is absent.
Capillaries – network is absent. The capillaries – network is present
Example: Phylum Arthropoda Example: Subphylum Vertebrate.

Question 15. Fill in the blanks:

  • Plasma without _________ factors is called serum.
  • ___________ and monocytes are phagocytic cells.
  • Eosinophils are associated with _________ reactions.
  • ____________ ions play a significant role in clotting.
  • One can determine the heart beat rate by counting the number of ________ in an ECG.

Answer 15:

  • Plasma without clotting factors is called serum.
  • Neutrophils and monocytes are phagocytic cells.
  • Eosinophils are associated with allergic reactions.
  • Calcium ions play a significant role in clotting.
  • One can determine the heart beat rate by counting the number of QRS complexes in an ECG.

Question 16. Explain the consequences of a situation in which blood does not coagulate.

Answer 16. Coagulation of the blood is the response of the body to injury. Blood coagulates to stop bleeding. Haemophilia is a genetic disease in which there is a deficiency of clotting factors like prothrombin, fibrinogen and vitamin K. Due to the deficiency of these factors, the blood does not coagulate and may result in death due to excessive and uncontrolled bleeding.

Question 17. Multiple choice questions:

  • An artificial pacemaker is grafted at the place of
  • Atrio-ventricular bundle
  • Purkinje fibres
  • Sinoatrial node
  • Atrio – ventricular bundle

Answer: c) Sinoatrial node.

Explanation: SA node is called the pacemaker of the heart.

  • The opening and closing of semilunar valves depend upon
  • Increased and decreased pressure in ventricles
  • Atrial systole
  • Duration of nerve impulse.
  • The quantity of blood present in the left ventricle.

Answer: a) increased and decreased pressure in ventricles.

  • The left atrium receives blood from the lungs through
  • Pulmonary vein
  • Aorta
  • Pulmonary artery
  • Vena cava

Answer: (a) Pulmonary vein

Explanation: Pulmonary vein is the only vein that carries oxygenated blood. It pours blood from the lungs to the left atrium.

Question 18. The walls of the ventricles are much thicker than atria. Explain.

Answer 18: The ventricles are thicker than atria because they pump blood to the body parts with pressure. The left ventricular wall is thicker than the right ventricular because the left ventricle pumps oxygenated blood to all parts of the body and the right ventricle pumps deoxygenated blood to the lungs, which are at a lesser distance from the heart.

Question 19. Why do we call our heart myogenic?

Answer 19. The Heart is called myogenic because heartbeats are generated by the muscle and not by the nerve. The activities of the heart are regulated intrinsically means they are autoregulated by specialised muscles.

Question 20. Explain heart sounds.

Answer 20. Heart sounds are the result of the closure of heart valves. There are two heart sounds, Lubb and Dupp, which repeat rhythmically.

The first heart sound is longer, louder and has a  lower frequency. It is created by the closure of the atrioventricular valves immediately after the beginning of the ventricular systole. The duration is  0.16 to 0.90 s.

The second heart sound is sharper with high frequency, soft and of short duration i.e, 0.10 s. This sound is created by the closure of the semilunar valve at the end of the ventricular systole.

Question 21. The Sino-atrial node is called the pacemaker of our heart. Why?

Answer 21: Our heart beats 70 – 75 times per minute. SA node is responsible for initiating and maintaining the rhythmic contractile activity of the heart. SA node generates heartbeat and is a bundle of specialised cardiac muscles which conducts impulses like nerve fibres. Due to these reasons, the SA node is called the pacemaker of the heart.

Question 22. What is meant by double circulation? What is its significance?

Answer 22: In double circulation, in order to complete one circulation, the blood passes twice through the heart:

  • To the lungs and back: This is called pulmonary circulation or lesser circulation due to less distance between the heart and the lungs.
  • To the body organs and back: This is called Systemic Circulation or greater circulation because of more distance between the heart and the organs.

The significance of double circulation is:

  • In pulmonary circulation, deoxygenated blood is passed to the lungs where oxygenated blood is carried out by the pulmonary veins into the left atrium of the heart.
  • In systemic circulation, pure blood is supplied to all the body parts.
  • To provide essential nutrients and oxygen to various parts of the body.
  • To take away carbon dioxide and harmful substances for elimination from different tissues of the body.

Double Ciculation Flowchart

Question 23. Why is blood considered a connective tissue?

Answer 23. Blood is derived from mesoderm. It has a composition of the fibre-free fluid matrix, plasma and other cells. It regularly circulates in the body and participates in the transportation of materials.

Question 24. Difference between P and T wave.

Answer 24: 

                          P wave                          T wave
Represent depolarisation. Represent repolarisation.
Represent electrical excitation of atria. Represent return of the ventricles from excited to the normal state.
Contraction of both the atria. The end of the T wave marks the end of systole.

Question 25. Differentiate between arteries and veins.

Answer 25.

                                      Arteries                                    Veins 
Carry blood from the heart to body parts. Bring back blood from body parts to the heart.
Thick-walled. Thin-walled
more elastic. Less elastic.
Lumen is narrow. Lumen is broad.
The blood flow is jerky or discontinuous. Continuous blood flow.
Carry blood away from the heart. Carry blood towards the heart.
Muscular  Non-muscular
Deep-seated Superficial under the skin.
All the arteries carry oxygenated blood All veins carry deoxygenated blood.
The exception is the pulmonary artery. The exception is the pulmonary vein.
Valves are absent Valves are present. This prevents the backflow of the blood.

Question 26. What is pulse pressure?

Answer 26: Pulse pressure is defined as the difference between systolic and diastolic pressure. Its normal value is 40 mm Hg in adults.

Question 27. What is the significance of the AV node and AV bundle in the functioning of the heart?

Answer 27: Atrioventricular node or AV node strengthens the signals arising from the SA node due to the weakening of these signals since ventricles are far away from the SA node. Atrioventricular bundles or AV bundles originate from the AV node and guide cardiac impulses further toward the walls of the ventricles.

Question 28. Describe events in the cardiac cycle.

Answer 28. The heart pumps blood to all the parts of the body. The cardiac cycle constitutes the changes which take place in the heart every heartbeat. The phase of contraction is called systole and, relaxation is called diastole. A single heartbeat consists of both the systole and diastole of the atria and ventricles. The cardiac cycle takes place in the following events:

  • Atrial systole: A wave of contraction is stimulated by the SA node. The blood flows from pulmonary veins and vena cava into left and right ventricles respectively, as tricuspid and bicuspid valves are open. The semilunar waves are closed. The atrial systole increases the blood flow into the ventricles. At the end of atrial systole, relaxation of atria and contraction of the ventricles simultaneously. The atrial systole occurs for 0.1 s and atrial diastole for 0.7 s.
  • Ventricular systole: The step involves simultaneous relaxation of the atria and contraction of the ventricles. With the contraction of the ventricles, the pressure of blood rises in them, and atrioventricular valves close rapidly to prevent the backflow of the blood from the ventricles to the atria. This is followed by the conduction of action potential by the AV node and AV bundle to the ventricular side.

Contraction of ventricle ——-> increase in ventricular pressure —- > closure of bicuspid and tricuspid valve

Due to this, pressure increases in great arteries like pulmonary and aortic arches —–> semilunar valves guide pulmonary artery ——->opening of aorta —–> blood enter into the ventricle from great arteries.

When ventricles relax, the pressure falls, which closes semilunar valves to prevent the backflow of blood into the ventricles.

A further drop in ventricular pressure opens bicuspid and tricuspid valves thereby allowing blood flow to the ventricles again.

Atria and ventricles are in a relaxed state and a new action potential is generated to start the next cardiac cycle.

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Q.1 Observe the given image, the labelled part of mammalian heart receives blood from



The superior vena cava is a large vein that carries deoxygenated blood from the upper half of the body to the heart’s right atrium. The inferior vena cava (or IVC) is the large vein that carries de-oxygenated blood from the lower half of the body into the right atrium of the heart.

Q.2 Identify the correct sequence of the chambers of the heart in order of thinnest to thickest walls.



Atria-Right ventricle-Left ventricle

The walls of the atria are thin because they only need enough pressure to move the blood into the ventricles. The ventricles possess thicker walls as compared to auricles. The left ventricle is with thickest walls because it has to pump blood throughout the body.

Q.3 If you have low level of red blood cells in your blood then you would have



Red blood cells transport oxygen to all body tissues. If our body will not produce red blood cells then we will feel fatigue due to lack of oxygen.

Q.4 Which of the following statements are true?
i. Pulse rate is not the same as the rate of the heartbeat.
ii. Wall of the left ventricle is thicker than the right one.
iii. Valves guard the opening between auricles and ventricles.
iv. Blood within the pulmonary vein returns to the right auricle.



Pulse rate is the same as the rate of the heartbeat. Blood within the pulmonary vein returns to the left auricle.

Q.5 Which of the following guards the left atrio-ventricular aperture in the human heart?



Bicuspid valve is one of the four valves of the heart. This valve is situated between the left atrium and the left ventricle. It permits blood to flow in one way only, from the left atrium into the left ventricle.

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FAQs (Frequently Asked Questions)

1. What is a good strategy to prepare well for Class 11 Biology

Understanding the concept of Biology can be tough for many students, especially when it comes to memorising terminologies and diagrams. The best way to understand the topic is to prepare it along with the help of a diagram. When you read any chapter topic and do not understand it, just try to match words with the given figure and you will definitely get a good grasp of the topic. Diagram and answer preparation must go hand in hand. If you understand a diagram well, then you can compose your answer in a  better way. They are also a good way of scoring good marks in exams.

2. Enumerate heart disorders.

The heart disorders are:

  • Ischemia 
  • Rheumatic heart disease
  • Persistent Ductus Arteriosus
  • Fibrillation 

3. How can Extramarks Important Questions Class 11 Biology Chapter 18 help me in scoring good marks?

Chapter 18 Class 11 Biology Important Questions are related to systemic circulation which includes heart, cardiac output, heartbeat, cardiac cycle and many other topics. Our question bank comes with detailed answers that are prepared by Biology expert faculty members. We have included necessary diagrams and flowcharts in our answers. This helps students to fully understand each of the given answers. By regularly practising questions from our question bank, students will be able to fully prepare the chapter and score very good marks in exams.

4. What is arteriosclerosis?

Arteriosclerosis refers to artery hardening due to old-age calcification.

5. What are vasodilators and vasoconstrictors in blood pressure?

Vasodilators like histamine decrease blood pressure and vasoconstrictor like adrenaline increase blood pressure.