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

NCERT Solutions for Class 11 Biology Chapter 18 Free PDF Download

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

Ans. The components of the formed elements in the blood are erythrocytes, leukocytes and platelets.

(a) Erythrocytes or red blood cells: These carry haemoglobin pigment (which contains oxygen) to all the cells of body.

(b) Leukocytes or white blood cells: These cells are of two types – granulocytes and agranulocytes.

(i) Granulocytes contain 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.

(ii) Agranulocytes are of two types– lymphocytes and monocytes. Lymphocytes generate immune responses against infecting agents, while monocytes are phagocytic in nature.

(c) Platelets or thrombocytes help in clotting of blood.

2. What is the importance of plasma proteins?

Ans. About 6-8% of content is plasma proteins. These are fibrinogen, globulins and albumins.

(a) Fibrinogens are needed for clotting or coagulation of blood.

(b) Globulins are involved in defense mechanisms of the body.

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

Ans. The correct match is as follows:

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

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

Ans. Connective tissues are made up of a matrix consisting of living cells and a non-living substance, called the ground substance. Blood is considered a connective tissue because it has a matrix. The living cell types are red blood cells (RBC), also called erythrocytes, and white blood cells (WBC), also called leukocytes. The fluid
portion of whole blood, its matrix, is commonly called plasma. It connects the body systems, transports oxygen and nutrients to all the parts of the body, and removes the waste products.

5. What is the difference between lymph and blood?

Ans. Difference between lymph and blood:

Lymph	Blood
It is a colourless fluid.	It is a red-coloured fluid that contains RBCs.
It contains plasma and lesser number of WBCs and platelets.	It contains plasma, RBCs, WBCs and platelets.
It lacks plasma proteins.	It has plasma proteins, calcium and phosphorus.
It has lymphatic vessels to transport nutrients from the tissue cells to the blood.	It transports nutrients and oxygen from one organ to another.
The flow of lymph is slow.	The blood flows very fast inside blood vessels.

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

Ans. Double circulation is type of circulation during which blood passes twice through the heart during one complete cycle. It is mainly found in birds and mammals. Their 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:

(a) Systemic circulation: In this type of circulation, the oxygenated blood flows from the left ventricle of the heart to the aorta. It is then carried by blood through a network of arteries, arterioles, and capillaries to the tissues. From the tissues, the deoxygenated blood is collected by the venules, veins, and vena cava, and is emptied into the left auricle.

(b) Pulmonary circulation: It involves the movement of deoxygenated blood from the right ventricle to the pulmonary artery. It then carries blood to the lungs for oxygenation. From the lungs, the oxygenated blood is carried by the pulmonary veins into the left atrium.

Therefore, blood has to pass alternately through the lungs and the tissues in double circulation.

Significance of double circulation: The separation of oxygenated and deoxygenated blood allows a more efficient supply of oxygen to the body cells.

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

Ans. (a) Difference between Blood and Lymph:

Blood	Lymph
It is a red-coloured fluid.	It is a colourless fluid.
It contains plasma, RBCs, WBCs, and platelets.	It lacks RBCs but contains plasma and lesser number of WBCs and platelets.
It also contains proteins.	It lacks proteins.
Blood transports gases and nutrients to different parts of body.	Lymph plays a role in the defensive system of the body.

(b) Difference between Open and Closed system of circulation:

Open system of circulation	Closed system of circulation
Blood is pumped by the heart, through large vessels, into body cavities called sinuses.	Blood is pumped by the heart, through a closed network of vessels.
The body tissues are in direct contact with blood.	The body tissues are not in direct contact with blood.
Blood flows at low pressure. Hence, it is a slower and less efficient system of circulation.	Blood flows at high pressure. Hence, it is a faster and more efficient system of circulation.
This system is present in arthropods and in some molluscs.	This system is present in annelids, echinoderms, and vertebrates.

Systole	Diastole
The process of contraction of heart muscles during the cardiac cycle is called systole.	The process of relaxation of heart muscles during the cardiac cycle is called diastole.
Systole decreases the volume of the heart chambers and forces the blood out of them.	Diastole brings the heart chambers back into their original sizes to receive more blood.

(d) Difference between P-wave and T-wave:

P-wave	T-wave
‘P’ wave is the first wave in an ECG and is a positive wave. It indicates the activation of the SA nodes.	‘T’ wave too is a positive wave and is the final wave in an ECG though sometimes an additional U wave may be seen. In an electrocardiogram (ECG), the T-wave represents ventricular relaxation.
Blood is received by the atria. So, it is of atrial origin.	T-Wave represents the repolarisation of ventricles. Blood is received by the atria.

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

Ans. The vertebrate heart has evolved from a two-chambered heart of a fish to a four-chambered heart of mammals and birds.

The evolutionary change in the pattern of heart among the vertebrates is described as follows:

(a) Fish heart: The heart of the fish is two-chambered. The heart pumps deoxygenated blood to the gills where it is oxygenated and sent to the body. The deoxygenated blood is carried to the heart.

(b) Amphibian’s heart: In amphibians, there are three chambers, i.e., the left atrium, the right atrium and a ventricle.

(i) The left atrium receives the oxygenated blood from the gills, the lungs or the skin.

(ii) The right atrium receives deoxygenated blood from the body organs.

(iii) Both types of blood are mixed in the ventricle and the body is supplied with the mixed blood.

(c) Reptilian heart: There is half septum which divides the ventricle incompletely. Here, oxygenated and deoxygenated blood do not mix. In crocodiles, the heart is completely divided like of higher organisms.

(d) Heart of birds and mammals: The heart is completely divided into halves which keep the oxygenated and deoxygenated blood separate.

9. Why do we call our heart myogenic?

Ans. The meaning of ‘myo’ is ‘muscle’, and ‘genic’ is ‘originating from’. The contractions in human heart are activated by a specially modified heart muscle known as the sinoatrial node that is located in the right atrium. So, the human heart is termed as myogenic.

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

Ans. The SA (sino-atrial) node is a specialised bundle of neurons located in the upper part of the right atrium of the heart. The cardiac impulse that originates from the SA node triggers a sequence of electrical events in the heart. It controls 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 also named as the natural pacemaker of the human body.

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

Ans. Atrio-ventricular node: The atrio-ventricular node or AV node electrically connects the heart's atria and ventricles to coordinate beating in the top of the heart. It gives rise to the bundle of His that conducts the cardiac impulses from the auricles to the ventricles. It is also capable of initiating impulses that cause contraction but at slower rate than SA node.

Atrio-ventricular bundle: The atrio-ventricular bundle (Bundle of His) is a mass of specialized fibres which originate from the AV node. It transmits electrical impulses from the AV node to the apex of the myocardium where the wave of ventricular contraction begins.

Hence, the atrio-ventricular node and the atrioventricular bundle play a role in the contraction of ventricles.

12. Define a cardiac cycle and the cardiac output.

Ans. Cardiac cycle: The cardiac cycle is a series of electrical and mechanical events that occur during the phases of heart relaxation (diastole) and contraction (systole).

Cardiac output: The volume of blood pumped per minute by each ventricle of the heart is called cardiac output. It’s average value is 5 litres in a healthy individual.

13. Explain heart sounds.

Ans. Heart sounds are created from blood flowing through the heart chambers as the cardiac valves open and close during the cardiac cycle. Vibrations of these structures from the blood flow create audible sounds.

In a healthy adult, the heart makes two sounds, commonly described as 'lub' and 'dub. The first sound called ‘lub’ happens when the mitral and tricuspid valves close. The second sound ‘dub’ happens when the aortic and pulmonary valves close after the blood has been squeezed out of the heart.

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

Ans. Standard ECG:

ECG is graphical record of the heart activities produced by the excitation of the cardiac muscles. The instrument used to record the changes is an electrocardiograph.

(a) Each peak in the ECG is identified with a letter from P to T that corresponds to a specific electrical activity of the heart.

(b) The P-wave represents the electrical excitation of the atria (depolarisation), which leads to their contraction. The QRS complex represents the depolarisation of the ventricles, which initiates the ventricular contraction. The contraction starts shortly after Q and marks the beginning of the systole.

(c) The T-wave represents the return of the ventricles from excited to normal state (repolarisation). The end of the T-wave marks the end of systole.

(d) By counting the number of QRS complexes that occur in a given time period, one can determine the heart beat rate of an individual.

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