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Q8:
Describe the evolutionary change in the pattern of heart among the vertebrates.
Solution :
Evolutionary Trend in Vertebrate Heart Structure
The evolution of the vertebrate heart reflects an increasing demand for metabolic efficiency and the separation of oxygenated and deoxygenated blood to support endothermy. This progression is characterized by an increase in the number of chambers and the development of internal septation.
Step 1: Pisces (Two-Chambered Heart)
In fishes, the heart is venous, meaning it receives only deoxygenated blood. It consists of two main chambers: one atrium and one ventricle.
- Structure: Sinus venosus $\rightarrow$ Atrium $\rightarrow$ Ventricle $\rightarrow$ Conus arteriosus.
- Mechanism: Blood is pumped to the gills for oxygenation and then flows directly to the systemic circulation [Single Circulation].
Step 2: Amphibians and Most Reptiles (Three-Chambered Heart)
Transitioning to land necessitated a more efficient delivery system, leading to a three-chambered structure.
- Structure: Two atria (Right/Left) and one undivided ventricle.
- Mechanism: While oxygenated and deoxygenated blood mix partially within the single ventricle, the heart is capable of delivering blood to both lungs (pulmonary) and the rest of the body (systemic) [Incomplete Double Circulation].
Step 3: Crocodiles, Birds, and Mammals (Four-Chambered Heart)
To support high metabolic rates and maintain constant body temperature (endothermy), complete separation of blood streams evolved.
- Structure: Two atria and two ventricles, separated by complete interatrial and interventricular septa.
- Mechanism: Deoxygenated blood enters the right side, while oxygenated blood enters the left side. There is zero mixing of blood [Complete Double Circulation].
Comparative Analysis Table
| Class | Chambers | Circulation Type | Oxygenation Status |
|---|---|---|---|
| Fishes | 2 (1A, 1V) | Single | Deoxygenated only |
| Amphibians/Reptiles | 3 (2A, 1V) | Incomplete Double | Mixed in ventricle |
| Birds/Mammals | 4 (2A, 2V) | Complete Double | Totally separated |
Visual Representation of Heart Evolution
Final Solution: The evolution of the vertebrate heart demonstrates a progression from a simple two-chambered venous heart in fishes to a three-chambered heart in amphibians and most reptiles, culminating in a complex, completely septated four-chambered heart in birds and mammals, thereby facilitating the transition from single to complete double circulation for increased physiological efficiency.
More Questions from Class 11 Biology Body Fluids and Circulation EXERCISES
- Q1: Name the components of the formed elements in the blood and mention one major function of each of them.
- Q2: What is the importance of plasma proteins?
- Q3: 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
- Q4: Why do we consider blood as a connective tissue?
- Q5: What is the difference between lymph and blood?
- Q6: What is meant by double circulation? What is its significance?
- Q7(a): Write the differences between : (a) Blood and Lymph
- Q7(b): Write the differences between : (b) Open and Closed system of circulation
- Q7(c): Write the differences between : (c) Systole and Diastole
- Q7(d): Write the differences between : (d) P-wave and T-wave
- Q9: Why do we call our heart myogenic?
- Q10: Sino-atrial node is called the pacemaker of our heart. Why?
- Q11: What is the significance of atrio-ventricular node and atrio-ventricular bundle in the functioning of heart?
- Q12: Define a cardiac cycle and the cardiac output.
- Q13: Explain heart sounds.
- Q14: Draw a standard ECG and explain the different segments in it.
CBSE Solutions for Class 11 Biology Body Fluids and Circulation
Chapters in CBSE - Class 11 Biology
- The Living World
- Biological Classification
- Plant Kingdom
- Animal Kingdom
- Morphology of Flowering Plants
- Anatomy of Flowering Plants
- Structural Organisation in Animals
- Cell – The Unit of Life
- Biomolecules
- Cell Cycle and Division
- Transport in Plants
- Mineral Nutrition
- Photosynthesis
- Respiration in Plants
- Plant Growth and Development
- Digestion and Absorption
- Breathing and Exchange of Gases
- Excretory Products and Elimination
- Locomotion and Movement
- Neural Control and Coordination
- Chemical Coordination and Integration
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