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

NCERT Class 11 Biology Chapter 15 Notes Body Fluids And Circulation: The human body relies on a well-organized transport system to deliver vital nutrients, oxygen, and hormones and remove metabolic waste at the same time. The system is composed of blood, lymph, and a circulatory network of blood vessels. The heart acts as a central organ, pumping blood constantly to feed life processes. Learning about these mechanisms is important for students studying with NCERT Notes for Class 11 since it is the basis of human physiology.

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This Story also Contains

1. Body Fluids and Their Composition
2. Blood Groups and Their Significance
3. Structure and Function of the Human Heart
4. Common Circulatory Disorders
5. Chapter-Wise NCERT Class 11 Notes Biology
6. Most Important Questions Class 11 Biology Chapter 15
7. Approach to Solve Questions of Class 11 Biology Chapter 15

Chapter 15 of NCERT Class 11 Biology Notes, Body Fluids and Circulation, discusses the structure of blood and lymph, the role of the heart, and various circulatory routes. This chapter also describes terms such as blood groups, cardiac cycle, and blood pressure control. Using NCERT Solutions, students can gain a better understanding of how the circulatory system is responsible for maintaining homeostasis to keep all the body organs functioning properly. Reading through these subjects by CBSE Notes helps in test preparation and improves conceptual clarity.

Also Read:

• NCERT Solutions for class 11 biology chapter 18 Body Fluid and Circulation.
• NCERT Exemplar Class 11 Biology Chapter 18 Solutions Body Fluid and Circulation

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 hemoglobin, 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.

Lymph: Functions and Comparison with Blood

Lymph is a colorless 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).

Subject Wise NCERT Exemplar Solutions

• NCERT Exemplar Class 11 Solutions
• NCERT Exemplar Class 11 Maths
• NCERT Exemplar Class 11 Physics
• NCERT Exemplar Class 11 Chemistry
• NCERT Exemplar Class 11 Biology

Blood Groups and Their Significance

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 on 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 mollusks. 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.

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

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 Life-style Changes

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

Chapter-Wise NCERT Class 11 Notes Biology

Most Important Questions Class 11 Biology Chapter 15

Body Fluids and Circulation is one of the major NEET and board exam chapters that explains how the circulatory system facilitates the transportation of vital substances such as oxygen, nutrients, hormones, and waste products of metabolism around the body. It includes very important topics such as composition and functions of blood and lymph, structure of the heart, mechanism of circulation, cardiac cycle, regulation of heart function, and general circulatory disorders.

Question: What is the major component of human blood?

1. a) Platelets
2. b) Plasma
3. c) Red blood cells
4. d) White blood cells

Answer: Plasma

Question: What is the role of red blood cells (RBCS)?

1. a) Defence against infection
2. b) Blood clotting
3. c) Oxygen transport
4. d) Production of antibodies

Answer: Oxygen transport

Question: What is referred to as the universal donor?

1. a) A
2. b) B
3. c) AB
4. d) O

Answer: O

Question: Which valve exists between the left atrium and left ventricle?

1. a) Tricuspid valve
2. b) Bicuspid (mitral) valve
3. c) Aortic valve
4. d) Pulmonary valve

Answer: Bicuspid (mitral) valve

Question: What stops the backflow of blood in veins?

1. a) Arterial pressure
2. b) Thin walls
3. c) Valves
4. d) Capillary action

Answer: Valves

Question: What is systolic pressure?

Answer: Systolic pressure is the pressure exerted by blood on the arterial walls when the ventricles contract. It is the higher reading in a blood pressure measurement (normal: ~120 mmHg).

Question: Define "cardiac output".

Answer: Cardiac output refers to the volume of blood pumped out by each ventricle within a minute. It is stroke volume × heart rate (normal: ~5 L/min in adults).

Question: What is the role of platelets in blood?

Answer: Platelets contribute to clotting of the blood by filling a plug in the site of injury and also releasing clotting factors.

Question: Differentiate between an artery and a vein.

Answer: Arteries transport blood from the heart under high pressure, possess thick muscular walls, and lack valves. Veins transport blood towards the heart under low pressure, have thinner walls, and possess valves to avoid backflow.

Question: What is the importance of the lymphatic system?

Answer: The lymphatic system brings interstitial fluid back into the bloodstream, absorbs fats from the digestive system, and aids in immune defence.

Match the following:

A. Erythrocytes – i. Oxygen transport

B. Platelets – ii. Blood clotting

C. Lymph – iii. Returns interstitial fluid

Options:

1. A-i, B-ii, C-iii
2. A-ii, B-i, C-iii
3. A-iii, B-i, C-ii
4. A-i, B-iii, C-ii

Answer: A-i, B-ii, C-iii

Approach to Solve Questions of Class 11 Biology Chapter 15

This chapter has direct, conceptual, and application-based questions. To prepare effectively:

• Study NCERT and Exemplar thoroughly for the concepts of blood and lymph composition, structure of human heart, types of circulation, cardiac cycle, blood pressure, and regulation of heart function.
• Practice sketching and labeling the diagrams of the human heart, double circulation pathway, internal structure of blood vessels, and ECG waveforms.
• Memorize the circulation of blood around the heart, the classes of blood vessels, the blood group compatibilities, and the most important terms such as cardiac output, stroke volume, systolic and diastolic pressure, and lymph.
• Answer questions with emphasis on the differences between the open and closed circulatory systems, pulmonary and systemic circulation, arteries and veins, and the functions of the components of blood in transportation and immunity.

Subject Wise NCERT Solutions

• NCERT Solutions for Class 11 Mathematics
• NCERT Solutions for Class 11 Chemistry
• NCERT Solutions for Class 11 Physics

• NCERT Solutions for Class 11 Biology

Body Fluids and Circulation is a basic chapter in human physiology that describes how the body maintains the ongoing delivery of oxygen and nutrients and effectively eliminates waste. The circulatory system, which includes blood, lymph, the heart, and blood vessels, is responsible for keeping the body in homeostasis and overall health. The understanding of this chapter makes students appreciate the significance of an efficient circulatory system and how it affects many physiological processes. A well-balanced lifestyle, proper nutrition, and appropriate exercise are necessary for good cardiovascular health and the prevention of circulatory disorders.