Assertion (A): The walls of the atria are thinner as compared to those of the ventricles.
Reason (R): The atria are the 'receiving chambers' as they receive blood and ventricles are the 'distributing chambers' as they pump blood into lungs and the thickest blood vessel - Aorta.
- Both A and R are true.
- Both A and R are false.
- A is true and R is false.
- A is false and R is true.
Both A and R are true.
Explanation — The atria have thinner walls as they only need to pump blood a short distance into the ventricles. Ventricles are bigger in size and their walls are thicker, elastic and muscular so as to efficiently pump blood to different parts of the body with much greater force.
Circulatory System – Interactive Study Guide
The circulatory system transports blood, oxygen, nutrients, and hormones throughout the body. It consists of the heart (pump), blood (transport medium), and blood vessels (pipelines).
Blood Components
| Component | Function | Key Fact |
|---|---|---|
| Plasma (55%) | Transports dissolved substances | 90% water, carries nutrients, hormones, waste |
| RBC | Carry oxygen | Biconcave disc, no nucleus, contain haemoglobin |
| WBC | Fight infections | Have nucleus, larger than RBC, immune defence |
| Platelets | Blood clotting | Cell fragments, no nucleus |
Blood Group Quick Reference
O = Universal Donor (no antigens) | AB = Universal Recipient (no antibodies)
| Group | Antigen | Antibody |
|---|---|---|
| A | A | anti-B |
| B | B | anti-A |
| AB | A & B | None |
| O | None | anti-A & anti-B |
Heart – Quick Facts
- 4 chambers: RA, RV, LA, LV
- 4 valves: Tricuspid (R), Bicuspid (L), 2 Semilunar
- Septum divides right (deoxy) from left (oxy)
- Left ventricle = thickest wall
Double Circulation
Pulmonary: RV → Pulmonary artery → Lungs → Pulmonary veins → LA
Systemic: LV → Aorta → Body → Vena cava → RA
Blood Vessels Comparison
| Arteries | Veins | Capillaries | |
|---|---|---|---|
| Direction | Away from heart | To heart | Connect A to V |
| Walls | Thick | Thin | 1 cell thick |
| Valves | No | Yes | No |
Self-Test Questions
- Why is the left ventricle wall thicker than the right?
- Draw and label the human heart.
- What is double circulation? Describe both circuits.
- Why is blood group O called universal donor?
- What is the function of valves in veins?