NCERT Solutions for Class 12th: Ch 18 Body Fluids and Circulation Biology
Exercises
Page No: 289
Answer
The components of the formed elements in the blood with their major function are:
→ Erythrocytes (RBC): The erythrocytes play a significant role in transport of respiratory gases.
→ Leucocytes (WBC): The leucocytes play an important role to fight against infections.
→ Leucocytes (WBC): The leucocytes play an important role to fight against infections.
→ Thrombocytes (Platelets): Platelets are involve in the coagulation or clotting of blood.
Answer
• Fibrinogen play important role in blood coagulation.
• Globulins protects the body against infecting agents
• Albumins helps in maintaining the fluid volume within the vascular space.
Column I
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Column II
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||
(a)
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Eosinophils
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(i)
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Coagulation
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(b)
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RBC
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(ii)
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Universal Recipient
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(c)
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AB Group
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(iii)
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Resist Infections
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(d)
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Platelets
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(iv)
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Contraction of Heart
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(e)
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Systole
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(v)
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Gas transport
|
Answer
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)
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Systole
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(iv)
|
Gas transport
|
4. Why do we consider blood as a connective tissue?
Answer
Blood as a connective tissue because:
→ Blood serves the purpose of connecting the body systems by transporting substances.
→ Blood is mesodermal in origin like any other connective tissues.
Answer
Lymph
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Blood
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| It is red-coloured fluid | It is a colourless fluid. |
| It contains plasma and lesser number of WBCs and platelets. | It contains plasma, RBCs, WBCs, and platelets. |
| Its plasma lacks proteins. | Its plasma has proteins, calcium, and phosphorus. |
| It transports nutrients from the tissue cells to the blood, through lymphatic vessels. | It transports nutrients and oxygen from one organ to another. |
| It helps in body defence and is a part of the immune system. | It helps in the circulation of oxygen and carbon dioxide. |
| The flow of lymph is slow. | The flow of blood in the blood vessels is fast. |
6. What is meant by double circulation? What is its significance?
Answer
→ Systemic circulation: In this circulation the oxygenated blood from the left ventricle of heart is pumped to all the body parts (except lungs) through aorta. After this, deoxygenated blood from various parts comes back to heart by superior and inferior vena cava into the right atria. This completes the 1st circulation.
→ Pulmonary circulation: In pulmonary circulation the deoxygenated blood brought back from body parts is pumped to lungs by the right ventricle through the pulmonary artery. In lungs deoxygenated blood is again converted back to oxygenated blood and sent back to the heart in left atria by pulmonary veins. This completes the 2nd circulation.
The most important significance of this system is that the oxygenated and deoxygenated blood does not mix anywhere in the body thus improves the oxygen supplying capacity of the heart.
(a) Blood and Lymph
(b) Open and Closed system of circulation
(c) Systole and Diastole
(d) P-wave and T-wave
Answer
(a) Blood and Lymph
(a) Blood and Lymph
Lymph
|
Blood
|
| It is a colourless fluid. | It is red-coloured fluid. |
| It contains plasma and lesser number of WBCs and platelets. | It contains plasma, RBCs, WBCs, and platelets. |
| It transports nutrients from the tissue cells to the blood, through lymphatic vessels. | It transports nutrients and oxygen from one organ to another. |
| It helps in body defence and is a part of the immune system. | It helps in the circulation of oxygen and carbon dioxide. |
(b) Open and Closed system of circulation
| Open system of circulation | Closed system of circulation |
| In this system, blood is pumped by the heart, through large vessels, into body cavities called sinuses. | In this system, 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 in indirect contact with blood.
|
| Blood flows at low pressure. | Blood flows at high pressure. |
Blood flow cannot be regulated.
|
Blood flow can be regulated
|
| This is present in arthropods and molluscs. | This is present in annelids, echinoderms, and vertebrates. |
(c) Systole and Diastole
Systole
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Diastole
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| It is the contraction of the heart chambers to drive blood into the aorta and the pulmonary artery. | It is the relaxation of the heart chambers between two contractions. |
| 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) P-wave and T-wave
Systole
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Diastole
|
| In an electrocardiogram (ECG), the P-wave indicates the activation of the Sino-atrial node. | In an electrocardiogram (ECG), the T-wave represents ventricular relaxation. |
| During this phase, the impulse of contraction is generated by the SA node, causing atrial depolarisation. | During this phase, the ventricles relax and return to their normal state. |
| It is of atrial origin. | It is of ventricular origin. |
8. Describe the evolutionary change in the pattern of heart among the vertebrates.
Answer
The heart of vertebrates evolved from the simple 2-chambered heart of fishes to complex multi-chambered hearts.
Fishes have a 2-chambered heart with an atrium and a ventricle. Amphibians and the reptiles except crocodiles have a 3-chambered heart with two atria and a single ventricle, whereas crocodiles, birds and mammals possess a 4-chambered heart with two atria and two ventricles.
In fishes the heart pumps out deoxygenated blood which is oxygenated by the gills and supplied to the body parts from where deoxygenated blood is returned to the heart (single circulation).
In amphibians and reptiles, the left atrium receives oxygenated blood from the gills/lungs/skin and the right atrium gets the deoxygenated blood from other body parts. However, they get mixed up in the single ventricle which pumps out mixed blood (incomplete double circulation).
In birds and mammals, oxygenated and deoxygenated blood received by the left and right atria respectively passes on to the ventricles of the same sides. The ventricles pump it out without any mixing up, i.e., two separate circulatory pathways are present in these organisms, hence, these animals have double circulation.
9. Why do we call our heart myogenic?
Answer
10. Sino-atrial node is called the pacemaker of our heart. Why?
Answer
Answer
The atrio-ventricular node and atrio-ventricular bundle has the ability to generate action potentials without any external stimuli. Their main function is to get excited by the action potential initiated by the Sino- atrial node and conduct the stimulus to the remaining part of the heart through which they branch thus helping in the rhythmic contraction and relaxation of the heart.
Answer
The sequential events taking place in the heart which is the contraction or systole and relaxation or diastole of both the atria and ventricles is called cardiac cycle.
The volume of blood pumped out by the ventricles in one minute is called the cardiac output.
13. Explain heart sounds.
Answer
Answer
The P-wave represents the electrical excitation or depolarization of the atria. Depolarisation of atria leads to atricular systole.
The QRS complex represents the depolarization of the ventricles which initiates ventricular systole.
The T-wave represents the return of the ventricles from excited to normal state (repolarisation). The end of T-wave marks the end of systole.