NCERT Class 11 Biology Chapter 18 Notes Body Fluids And Circulation- Download PDF Notes

NCERT Class 11 Biology Chapter 18 Notes Body Fluids And Circulation- Download PDF Notes

Edited By Irshad Anwar | Updated on Jul 09, 2025 03:33 PM IST

Have you ever thought about how oxygen and nutrients travel all through your body? The NCERT Class 11 Biology Chapter 15 Notes Body Fluids and Circulation explain this in a simple, easy-to-follow way. These notes include clear points, labelled diagrams, and solved questions so you can revise quickly without confusion. You will read about blood, lymph, the heart, blood vessels, and the double circulation system, all explained properly as per the NCERT book. These NCERT Notes also work well if you need a fast recap before board exams or NEET.

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  1. Download NCERT Notes for Class 11 Chapter 15 PDF
  2. NCERT Notes for Class 11 Chapter 15
  3. Chapter 15 Previous Year Questions and Answers
  4. Chapter-Wise NCERT Class 11 Notes Biology
NCERT Class 11 Biology Chapter 18 Notes Body Fluids And Circulation- Download PDF Notes
NCERT Class 11 Biology Chapter 18 Notes Body Fluids And Circulation- Download PDF Notes

In these NCERT Class 11 Biology Notes of Chapter 15, you will find short, organised explanations of the structure of the heart, the working of valves, the cardiac cycle, and how blood pressure is controlled. Diagram suggestions are also included so you can improve how you present your answers. All points are set in order so you can go through them smoothly. Using these NCERT Notes for Class 11, students can build confidence in circulatory system topics and connect them with other chapters in human physiology.

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Download NCERT Notes for Class 11 Chapter 15 PDF

Having the notes in PDF format is beneficial because you can access them anytime without needing the internet. It helps you revise faster, stay organised, and keep all key points in one place. You can also read it on any device, highlight important terms, and go back to topics easily whenever needed. You can now download the NCERT Class 11 Biology Chapter 15 Notes Body Fluids and Circulation PDF for clear and quick exam preparation.

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NCERT Notes for Class 11 Chapter 15

The chapter, Body Fluids and Circulation, helps you understand how blood and other fluids deliver oxygen and nutrients, and remove wastes to keep every part of your body working smoothly. It talks about the heart’s structure, blood vessels, the cardiac cycle, and even how the body defends itself, all explained in a simple, clear way. These Chapter 15 NCERT Notes also make tricky diagrams and key terms easier to remember, making them great for quick revision and for anyone looking for Class 11 Body Fluids and Circulation Notes PDF Download.

Body Fluids and Their Composition

In living organisms, body fluids have an important role in the transportation of nutrients, gases, and waste products. Blood and lymph are the two principal body fluids in humans.

Blood: Structure and Functions

Blood is a specialized connective tissue that has critical functions, including the transport of oxygen, immunity, and homeostasis. It contains:

  • Plasma: The liquid component of blood, which constitutes approximately 55% of its volume. Plasma consists of water (90-92%), proteins (albumin, globulin, fibrinogen), electrolytes, nutrients, hormones, and waste products. Plasma aids in transport and clotting.
  • Red Blood Cells (RBCs): Also referred to as erythrocytes, they have haemoglobin, which is responsible for binding oxygen and transporting it to tissues. RBCs do not have a nucleus in mammals and live for approximately 120 days.
  • White Blood Cells (WBCs): Also referred to as leukocytes, they are important for immunity. They are of five types – neutrophils, eosinophils, basophils, lymphocytes, and monocytes – each with a particular immune function.
  • Platelets (Thrombocytes): These assist in blood clotting by releasing clotting factors that create a fibrin mesh, stopping excessive blood loss.

compostion of blood

Lymph

Lymph is a colourless fluid that is obtained from blood plasma. Unlike blood, it does not contain RBCs and contains less protein. Its roles are as follows:

  • Transport of vitamins and fatty acids from the intestine to the blood.
  • Assisting in immune function by transporting lymphocytes.
  • Removal of excess interstitial fluid to avoid tissue swelling (edema).

Formed Elements

Formed elements include erythrocytes (RBCs), leucocytes (WBCs), and platelets. They make up about 45% of blood volume.

Erythrocytes (Red Blood Cells, RBCs)

  • Most abundant blood cells: ~5–5.5 million per mm³ of blood in adults.
  • Produced in red bone marrow.
  • Biconcave, no nucleus in most mammals.
  • contains haemoglobin (12–16 g/100 ml), responsible for oxygen transport and red colour.
  • Life span: ~120 days; destroyed in the spleen (“graveyard of RBCs”).

Leucocytes (White Blood Cells, WBCs)

  • Colourless, nucleated, fewer in number: 6000–8000 per mm³ of blood.
  • Short-lived cells.

The two categories of leucocytes are:

Granulocytes

  1. Neutrophils: most abundant WBCs (60–65%), phagocytic
  2. Monocytes: phagocytic, 6–8%
  3. Basophils: rarest (0.5–1%), secrete histamine, serotonin, and heparin (inflammation)
  4. Eosinophils: 2–3%, resist infections and are linked to allergies

Agranulocytes

  1. Lymphocytes: 20–25%, B and T types, responsible for immune responses
  2. Platelets (Thrombocytes)
  3. Fragments of megakaryocytes in bone marrow
  4. Count: 1,50,000–3,50,000 per mm³ of blood
  5. Help in blood clotting by releasing substances involved in coagulation
  6. Low platelet count can cause clotting disorders and excessive bleeding

Blood Groups and Their Significance

Knowing a person’s blood group is important for safe blood transfusions, organ transplants, and even during pregnancy to avoid complications like hemolytic disease of the newborn. Blood groups are grouped based on the absence or presence of certain antigens on RBC surfaces. There are two major group systems:

ABO Blood Group System

Established by Karl Landsteiner, this is based on the presence of antigen A and antigen B on RBCs and plasma antibodies accordingly:

  • Type A: Antigen A on RBCs, Anti-B antibodies in plasma.
  • Type B: Antigen B on RBCs, Anti-A antibodies in plasma.
  • Type AB: Both A and B antigens on RBCs, neither antibodies (universal recipient).
  • Type O: No A or B antigens, both Anti-A and Anti-B antibodies (universal donor).

Rh Factor and Its Medical Significance

  • The Rh factor is a second antigen (Rh antigen or D antigen) found in RBCs.
  • People with Rh antigens are Rh-positive (Rh⁺), and those who lack it are Rh-negative (Rh⁻).
  • An Rh⁻ mother who is pregnant with an Rh⁺ baby may develop hemolytic disease of the newborn (HDN), in which maternal antibodies destroy fetal RBCs.

Circulatory Pathways in Humans

Blood circulation may take various forms based on the complexity of an organism.

Open vs. Closed Circulatory System

  • Open Circulatory System: Arthropods and molluscs. Blood (hemolymph) moves freely in body cavities without enclosed vessels.
  • Closed Circulatory System: Annelids and vertebrates. Blood travels through a network of blood vessels, with effective oxygen and nutrient supply.

Circulatory Pathways

Single vs. Double Circulation

  • Single Circulation: Blood moves through the heart once per cycle (e.g., fishes).
  • Double Circulation: Blood circulates through the heart twice in each cycle (e.g., humans, birds, mammals), making oxygenation more efficient.

Pulmonary and Systemic Circulation

  • Pulmonary Circulation: Delivers deoxygenated blood from the heart to the lungs to be oxygenated.
  • Systemic Circulation: Supplies oxygenated blood from the heart to body tissues and brings back deoxygenated blood.

Structure and Function of the Human Heart

The human heart is a four-chambered muscular organ in the thoracic cavity.

Anatomy of the Heart

  • Right Atrium and Right Ventricle: Accept deoxygenated blood and send it to the lungs.
  • Left Atrium and Left Ventricle: Accept oxygenated blood and send it to the body.
  • Valves (Tricuspid, Bicuspid, Pulmonary, Aortic): Stop backflow and control blood movement.

Cardiac Cycle and Heartbeat Regulation

The cardiac cycle involves systole (contraction) and diastole (relaxation) for rhythmic blood flow. The normal heartbeat of a human is 72 beats a minute.

Function of SA Node and AV Node

  • Sinoatrial (SA) Node: Pacemaker of the heart, creating electrical impulses.
  • Atrioventricular (AV) Node: Impulse delay, facilitating coordinated contraction.

Blood Vessels and Their Functions

Three types of blood vessels transport blood:

  • Arteries: Carry oxygenated blood (except pulmonary artery) under high pressure.

  • Veins: Carry deoxygenated blood (except pulmonary vein) with valves to prevent backflow.

  • Capillaries: Facilitate gas and nutrient exchange at the tissue level.

Mechanism of Blood Circulation

The process of blood circulation is described as:

Blood Pressure and Pulse Rate

  • Blood Pressure (BP): Pressure blood exerts against vessel walls. Normal BP is 120/80 mmHg.
  • Pulse Rate: Heartbeat rate per minute, showing the heart's condition.

Regulation of Circulation by Hormones and the Nervous System

  • The medulla oblongata regulates heart rate and BP.
  • Hormones such as adrenaline elevate heart rate, while acetylcholine decreases it.
  • The sequential event in the heart which is cyclically repeated is called the cardiac cycle.

Common Circulatory Disorders

Some common circulatory disorders are:

1. High Blood Pressure (Hypertension)

  • BP greater than 140/90 mmHg can lead to heart disease.
  • Resulting from stress, obesity, and salt consumption in excess.

2. Atherosclerosis

  • Atherosclerotic plaques of cholesterol contract the arteries and curtail the circulation of blood.
  • Results in heart attacks and stroke.

3. Stroke

  • Damaged or ruptured cerebral vessels produce paralysis or loss of speech.

4. Heart Attack (Myocardial Infarction)

  • Closure in coronary vessels halts heart muscle oxygen, which results in injury to muscle tissues.

Prevention and Lifestyle Changes

  • Optimal diet (low cholesterol, low salt).
  • Regular exercise to maintain BP and circulation.
  • Stress management and avoiding smoking/alcohol.

Also Read

Chapter 15 Previous Year Questions and Answers

Some of the questions which have come in past years from the chapter are given below:

Question 1. What would be the cardiac output of a person having 72 heartbeats per minute and a stroke volume of 50 mL?

Option 1. 360 mL

Option 2. 3600 mL

Option 3. 7200 mL

Option 4. 5000 mL

Answer :

The volume of blood the heart pumps in a minute is known as cardiac output, and it is measured in litres per minute. It makes sense that cardiac output is equal to the product of heart rate (the number of beats per minute) and stroke volume.
Cardiac output= Stroke volume X heart rate

=50X72

=3600mL

Hence, the correct answer is Option (2) 3600 ml

Question 2. Which of the following statements is incorrect?

Option 1. A person of ‘O’ blood group has anti ‘A’ and anti ‘B’ antibodies in his blood plasma.

Option 2. A person of ‘B’ blood group can’t donate blood to a person of ‘A’ blood group.

Option 3. Blood group is designated on the basis of the presence of antibodies in the blood plasma.

Option 4. A person of AB blood group is a universal recipient.

Answer :

Blood group is based on the presence or absence of antigens A and B on RBCs and presence or absence of two natural antibodies present in plasma.

Hence, the correct answer is the option (3) Blood group is designated on the basis of the presence of antibodies in the blood Plasma.

Question 3. Which of the following correctly explains a phase/ event in the cardiac cycle in a standard electrocardiogram?

Option 1. QRS complex indicates atrial contraction.

Option 2. QRS complex indicates ventricular contraction.

Option 3. The time between S and T represents atrial systole.

Option 4. P-wave indicates the beginning of ventricular contraction.

Answer :

Ventricular contraction is caused by the depolarization of the ventricles, which is represented by the QRS complex in a normal electrocardiogram (ECG/EKG).
The electrical signal that triggers the ventricular muscles' mechanical contraction is known as depolarization.
Because it causes blood to be pumped from the ventricles into the aorta and pulmonary artery, this stage of the cardiac cycle is crucial.

Hence, the correct answer is option 2) QRS complex indicates ventricular contraction.

Also Read:

Chapter-Wise NCERT Class 11 Notes Biology

Here, students can find the notes of all chapters that explain all topics clearly and help in quick revision for exams.


Frequently Asked Questions (FAQs)

1. What are the main components of blood in Class 11 Biology?

Blood is composed of plasma (liquid component), red blood cells (RBCs), white blood cells (WBCs), and platelets. Plasma carries nutrients, RBCs transport oxygen, WBCs combat infection, and platelets assist in blood clotting.

2. How does blood circulation occur in the human body?

The heart circulates oxygenated blood by arteries to the tissues of the body and collects deoxygenated blood via veins. The pulmonary circulation transmits gases within the lungs, whereas systemic circulation delivers oxygen to tissues.

3. What is the difference between open and closed circulatory systems?
  • Open Circulatory System: Blood is freely flowing in body cavities without having enclosed vessels (e.g., arthropods).
  • Closed Circulatory System: Blood is kept within vessels for effective transport (e.g., humans, vertebrates).
4. How is oxygen transported in the blood?

Oxygen gets attached to hemoglobin in RBCs, making oxyhemoglobin. It is carried to tissues by arteries, and it is released for cellular respiration, whereas carbon dioxide is transported back to the lungs for expulsion.

5. What is the role of the heart in blood circulation?

The heart sends blood around the body through periodic contractions. It delivers oxygenated blood to tissues and carbon dioxide-laden blood to the lungs to be cleaned through pulmonary circulation.

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A block of mass 0.50 kg is moving with a speed of 2.00 ms-1 on a smooth surface. It strikes another mass of 1.00 kg and then they move together as a single body. The energy loss during the collision is

Option 1)

0.34\; J

Option 2)

0.16\; J

Option 3)

1.00\; J

Option 4)

0.67\; J

A person trying to lose weight by burning fat lifts a mass of 10 kg upto a height of 1 m 1000 times.  Assume that the potential energy lost each time he lowers the mass is dissipated.  How much fat will he use up considering the work done only when the weight is lifted up ?  Fat supplies 3.8×107 J of energy per kg which is converted to mechanical energy with a 20% efficiency rate.  Take g = 9.8 ms−2 :

Option 1)

2.45×10−3 kg

Option 2)

 6.45×10−3 kg

Option 3)

 9.89×10−3 kg

Option 4)

12.89×10−3 kg

 

An athlete in the olympic games covers a distance of 100 m in 10 s. His kinetic energy can be estimated to be in the range

Option 1)

2,000 \; J - 5,000\; J

Option 2)

200 \, \, J - 500 \, \, J

Option 3)

2\times 10^{5}J-3\times 10^{5}J

Option 4)

20,000 \, \, J - 50,000 \, \, J

A particle is projected at 600   to the horizontal with a kinetic energy K. The kinetic energy at the highest point

Option 1)

K/2\,

Option 2)

\; K\;

Option 3)

zero\;

Option 4)

K/4

In the reaction,

2Al_{(s)}+6HCL_{(aq)}\rightarrow 2Al^{3+}\, _{(aq)}+6Cl^{-}\, _{(aq)}+3H_{2(g)}

Option 1)

11.2\, L\, H_{2(g)}  at STP  is produced for every mole HCL_{(aq)}  consumed

Option 2)

6L\, HCl_{(aq)}  is consumed for ever 3L\, H_{2(g)}      produced

Option 3)

33.6 L\, H_{2(g)} is produced regardless of temperature and pressure for every mole Al that reacts

Option 4)

67.2\, L\, H_{2(g)} at STP is produced for every mole Al that reacts .

How many moles of magnesium phosphate, Mg_{3}(PO_{4})_{2} will contain 0.25 mole of oxygen atoms?

Option 1)

0.02

Option 2)

3.125 × 10-2

Option 3)

1.25 × 10-2

Option 4)

2.5 × 10-2

If we consider that 1/6, in place of 1/12, mass of carbon atom is taken to be the relative atomic mass unit, the mass of one mole of a substance will

Option 1)

decrease twice

Option 2)

increase two fold

Option 3)

remain unchanged

Option 4)

be a function of the molecular mass of the substance.

With increase of temperature, which of these changes?

Option 1)

Molality

Option 2)

Weight fraction of solute

Option 3)

Fraction of solute present in water

Option 4)

Mole fraction.

Number of atoms in 558.5 gram Fe (at. wt.of Fe = 55.85 g mol-1) is

Option 1)

twice that in 60 g carbon

Option 2)

6.023 × 1022

Option 3)

half that in 8 g He

Option 4)

558.5 × 6.023 × 1023

A pulley of radius 2 m is rotated about its axis by a force F = (20t - 5t2) newton (where t is measured in seconds) applied tangentially. If the moment of inertia of the pulley about its axis of rotation is 10 kg m2 , the number of rotations made by the pulley before its direction of motion if reversed, is

Option 1)

less than 3

Option 2)

more than 3 but less than 6

Option 3)

more than 6 but less than 9

Option 4)

more than 9

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