NCERT Solutions Class 11 Biology Chapter 18 - Body Fluids and Circulation

Q1: Name the components of the formed elements in the blood and mention one major function of each of them. 
Ans: The component elements in the blood are:
(i) Erythrocytes: They are the most abundant cells and contain the red pigment called haemoglobin. They carry oxygen to all parts of the body. Red blood cells are produced continuously in some parts of the body, such as the marrow of long bones, ribs, etc. There are about 4 – 6 million RBCs per cubic millimetre of blood.

Erythrocytes

(ii) Leukocytes: Leukocytes are colourless cells. These cells do not contain haemoglobin.
They are the largest cells of the body and are divided into two main categories:
(a) Granulocytes: These leucocytes have granules in their cytoplasm and include neutrophils, eosinophils, and basophils. Neutrophils are phagocytic cells that protect the body against various infecting agents. Eosinophils are associated with allergic reactions, while basophils are involved in inflammatory responses.

Granulocytes

(b) Agranulocytes: Lymphocytes and monocytes are agranulocytes. Lymphocytes generate immune responses against infecting agents, while monocytes are phagocytic in nature.
(iii) Platelets: Platelets are small irregular bodies present in the blood. They contain essential chemicals that help in clotting. The main function of platelets is to promote clotting.Platelets

Q2: What is the importance of plasma proteins? 
Ans: Plasma is the colourless fluid of blood which helps in the transport of food, CO₂, waste products, and salts. It constitutes about 55% of blood. About 6.8% of the plasma is constituted by proteins such as fibrinogens, globulins, and albumins.

• Fibrinogen is a plasma glycoprotein synthesised by the liver. It plays a role in the clotting of blood. Globulin is a major protein of the plasma. It protects the body against infecting agents. Albumin is a major protein of the plasma. It helps in maintaining the fluid volume within the vascular space.

Plasma Protein

Q3: Match column I with column II:

Ans:

Q4:  Why do we consider blood as a connective tissue?
Ans: Connective tissues have cells scattered throughout an extracellular matrix. They connect different body systems.
Blood is considered a type of connective tissue because of two reasons:

Connective Tissue

• Like the other connective tissues, blood is mesodermal in origin.
• It connects the body systems, transports oxygen and nutrients to all the parts of the body, and removes the waste products. Blood has an extra-cellular matrix called plasma, with red blood cells, white blood cells, and platelets floating in it.

Q5: What is the difference between lymph and blood?
Ans:

 
Q6: What is meant by double circulation? What is its significance?
Ans: Double circulation is a process during which blood passes twice through the heart during one complete cycle.
Double Circulation This type of circulation is found in amphibians, reptiles, birds, and mammals. However, it is more prominent in birds and mammals as in them the heart is completely divided into four chambers – the right atrium, the right ventricle, the left atrium, and the left ventricle.
The movement of blood in an organism is divided into two parts:
1. Systemic circulation
2. Pulmonary circulation

• Systemic circulation involves the movement of oxygenated blood from the left ventricle of the heart to the aorta. The blood then carries it through a network of arteries, arterioles, and capillaries to the tissues. The venules, veins collect the deoxygenated blood, and vena cava from the tissues and is emptied into the left auricle. 
• Pulmonary circulation involves the movement of deoxygenated blood from the right ventricle to the pulmonary artery, which then carries blood to the lungs for oxygenation. From the lungs, the oxygenated blood is carried by the pulmonary veins into the left atrium.

Hence, in double circulation, blood has to pass alternately through the lungs and the tissues.
Significance of double circulation: The separation of oxygenated and deoxygenated blood allows a more efficient supply of oxygen to the body cells. Blood is circulated to the body tissues through systemic circulation and to the lungs through the pulmonary circulation.

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
Ans: (a) Blood and lymph
(b) Open and closed systems of circulation
(c) Systole and diastole
(d) P-wave and T-wave

Q8: Describe the evolutionary change in the pattern of heart among the vertebrates.
Ans:  The pattern of the heart has evolved among vertebrates, showing increasing complexity. 

• Fishes have a 2-chambered heart consisting of one atrium and one ventricle. The heart pumps deoxygenated blood to the gills for oxygenation, and the oxygenated blood is distributed to the body (single circulation).
• Amphibians and reptiles (except crocodiles) have a 3-chambered heart with two atria and one ventricle. Oxygenated blood from the lungs or gills enters the left atrium, while deoxygenated blood from the body enters the right atrium. Both types of blood mix in the single ventricle and are pumped out, resulting in incomplete double circulation.
• Crocodiles, birds, and mammals have a 4-chambered heart with two atria and two ventricles. This allows for complete separation of oxygenated and deoxygenated blood, resulting in double circulation, where the blood flows in two separate pathways without mixing.

Q9: Why do we call our heart myogenic?
Ans: In the human heart, contraction is initiated by a specially modified heart muscle known as sinoatrial node. It is located in the right atrium. The SA node has the inherent power of generating a wave of contraction and controlling the heartbeat. Hence, it is known as the pacemaker. Since the SA node initiates the heartbeat and the impulse of contraction originates in the heart itself, the human heart is termed myogenic. The hearts of vertebrates and molluscs are also myogenic.

Q10: Sino-atrial node is called the pacemaker of our heart. Why?
Ans: The sino-atrial (SA) node is a specialised bundle of neurons located in the upper part of the heart's right atrium. The cardiac impulse originating from the SA node triggers a sequence of electrical events in the heart, thereby controlling the sequence of muscle contraction that pumps blood out of the heart. Since the SA node initiates and maintains the rhythmicity of the heart, it is known as the natural pacemaker of the human body.

Q11: What is the significance of atrio-ventricular node and atrio-ventricular bundle in the functioning of heart?
Ans: The atrioventricular (AV) node is present in the right atrium, near the base of the interauricular septum that separates the right auricle from the ventricle. It gives rise to the bundle of His that conducts the cardiac impulses from the auricles to the ventricles. 

• As the bundle of His passes the ventricle along the inter-ventricular septum, it divides into two branches – the right ventricle and the left ventricle. The end branches of this conducting system then form a network of Purkinje fibres that penetrate the myocardium. 
• The auricular contraction initiated by the wave of excitation from the sinoatrial node (SA node) stimulates the atrio-ventricular node, thereby leading to ventricles' contraction through the bundle of His and Purkinje fibres. Hence, the atrioventricular node and the atrioventricular bundle play a role in the contraction of ventricles.

Q12: Define a cardiac cycle and cardiac output.
Ans: The cardiac cycle is defined as the complete cycle of events in the heart from the beginning of one heartbeat to the beginning of the next. It comprises three stages – atrial systole, ventricular systole, and complete cardiac diastole.

Cardiac output is defined as the amount of blood pumped out by the ventricles in a minute.

Q13: Explain heart sounds.
Ans: Heart sounds are noises generated by the closing and opening of the heart valves. In a healthy individual, there are two normal heart sounds called lub and dub. Lub is the first heart sound. It is associated with the closure of the tricuspid and bicuspid valves at the beginning of systole. The second heart sound dub is associated with the closure of the semilunar valves at the beginning of diastole.
These sounds provide important information about the condition and working of the heart.Heart Sounds
Q14: Draw a standard ECG and explain the different segments in it.
Ans: An electrocardiogram is a graphical representation of the cardiac cycle produced by an electrograph.
The diagrammatic representation of a standard ECG is shown below:

ECG