Body Fluids and Circulation
NCERT Class 11 Biology • Chapter 15 Solutions
Blood & Lymph Composition
1. Name the components of the formed elements in the blood and mention one major function of each.
[Image of Blood cells composition]
| Component | Common Name | Major Function |
|---|---|---|
| Erythrocytes | Red Blood Cells (RBC) | Transport of respiratory gases ($O_2$ and $CO_2$). |
| Leucocytes | White Blood Cells (WBC) | Defense mechanism against infections (Immunity). |
| Thrombocytes | Platelets | Blood clotting (Coagulation). |
2. What is the importance of plasma proteins?
Plasma constitutes 55% of blood. Major plasma proteins and their functions are:
- Fibrinogen: Essential for clotting or coagulation of blood.
- Globulins: Primarily involved in defense mechanisms (antibodies) of the body.
- Albumins: Help in maintaining osmotic balance (BCOP).
3. Match Column I with Column II.
| Column I | Column II |
|---|---|
| (a) Eosinophils | (iii) Resist Infections (allergic reactions) |
| (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?
Blood is considered a specialized connective tissue because:
- Origin: It is mesodermal in origin, like other connective tissues.
- Matrix: It has a fluid matrix called plasma.
- Function: It connects different body systems by transporting nutrients, hormones, and gases between them.
5. What is the difference between lymph and blood?
| Feature | Blood | Lymph |
|---|---|---|
| Colour | Red (due to Haemoglobin). | Colourless. |
| RBCs | Present. | Absent. |
| Proteins | Contains more proteins, Ca, P. | Contains fewer proteins. |
| Flow | Fast velocity. | Slow velocity. |
| Function | Transport of gases, nutrients. | Transport of fats, immune response. |
Circulation Types & Heart Evolution
6. What is meant by double circulation? What is its significance?
[Image of Double Circulation Schematic]
Double Circulation: A system where blood passes through the heart twice in one complete cycle. It involves two distinct pathways:
- Pulmonary Circulation: Heart $\to$ Lungs $\to$ Heart (Deoxygenated blood becomes oxygenated).
- Systemic Circulation: Heart $\to$ Body Tissues $\to$ Heart (Oxygenated blood becomes deoxygenated).
Significance: It prevents the mixing of oxygenated and deoxygenated blood, ensuring a highly efficient supply of oxygen to the body, which is crucial for warm-blooded animals (mammals/birds) to maintain body temperature.
7. Write differences between various terms.
(a) Blood vs Lymph: (See Question 5).
(b) Open vs Closed Circulation:
- Open: Blood pumped into open spaces (sinuses). Direct contact with tissues. (e.g., Arthropods).
- Closed: Blood flows through closed vessels (arteries, veins). No direct contact. (e.g., Annelids, Chordates).
(c) Systole vs Diastole:
- Systole: Contraction phase of heart chambers (pumps blood out).
- Diastole: Relaxation phase of heart chambers (fills with blood).
(d) P-wave vs T-wave:
- P-wave: Represents electrical excitation (depolarisation) of Atria.
- T-wave: Represents return of ventricles from excited to normal state (repolarisation).
8. Evolutionary change in the pattern of heart among vertebrates.
[Image of Heart Evolution: Fish to Mammal]
- Pisces (Fish): 2-chambered heart (1 Atrium, 1 Ventricle). Single circulation. Pumps deoxygenated blood.
- Amphibians: 3-chambered heart (2 Atria, 1 Ventricle). Mixed blood pumped.
- Reptiles: 3-chambered (incomplete partition in ventricle). Exceptions like crocodiles have 4 chambers.
- Aves & Mammals: 4-chambered heart (2 Atria, 2 Ventricles). Complete separation of oxygenated and deoxygenated blood. Double circulation.
9. Why do we call our heart myogenic?
The human heart is called Myogenic (originating from muscle) because the cardiac impulse (heartbeat) originates within the specialized cardiac muscles (nodal tissue) of the heart itself, rather than from the nervous system (Neurogenic).
Cardiac Cycle & ECG
10. Sino-atrial (SA) node is called the pacemaker of our heart. Why?
The SA node is called the Pacemaker because:
- It can generate the maximum number of action potentials (70-75 min$^{-1}$).
- It is responsible for initiating and maintaining the rhythmic contractile activity of the heart.
11. Significance of AV node and AV bundle.
- Atrio-Ventricular (AV) Node: It receives the impulse from the SA node and introduces a slight delay (0.1s). This delay ensures that the atria contract and empty completely before the ventricles contract.
- Atrio-Ventricular (AV) Bundle (Bundle of His): It is the only electrical connection between the atria and ventricles. It transmits the impulse from the AV node to the Purkinje fibres, causing ventricular contraction.
12. Define cardiac cycle and cardiac output.
Cardiac Cycle: The sequential event in the heart which is cyclically repeated is called the cardiac cycle. It consists of systole and diastole of both atria and ventricles. Duration $\approx 0.8$ seconds.
Cardiac Output: The volume of blood pumped out by each ventricle per minute.
$$ \text{Cardiac Output} = \text{Stroke Volume} \times \text{Heart Rate} $$
$$ \approx 70 \text{ ml} \times 72 \text{ beats/min} \approx 5040 \text{ ml/min} \approx 5 \text{ Litres} $$
13. Explain heart sounds.
Doctors use a stethoscope to hear two prominent sounds during each cardiac cycle:
- First Sound (LUB): Low pitched, longer duration. Associated with the closure of the Tricuspid and Bicuspid valves at the beginning of ventricular systole.
- Second Sound (DUB): High pitched, shorter duration. Associated with the closure of the Semilunar valves at the end of ventricular systole (beginning of diastole).
14. Draw a standard ECG and explain the different segments.
Electrocardiogram (ECG): Graphical representation of the electrical activity of the heart.
- P-Wave: Represents the electrical excitation (depolarisation) of the atria, which leads to atrial contraction.
- QRS Complex: Represents the depolarisation of the ventricles, which initiates ventricular contraction. The contraction starts shortly after Q.
- 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.