CIE iGCSE Co-ordinated Sciences-B9.1 Circulatory systems - Study Notes- New Syllabus
CIE iGCSE Co-ordinated Sciences-B9.1 Circulatory systems – Study Notes
CIE iGCSE Co-ordinated Sciences-B9.1 Circulatory systems – Study Notes -CIE iGCSE Co-ordinated Sciences – per latest Syllabus.
Key Concepts:
Core
- Describe the circulatory system as a system of blood vessels with a pump and valves to ensure one-way flow of blood
- Describe the single circulation of a fish
- Describe the double circulation of a mammal
- Explain the advantages of a double circulation
CIE iGCSE Co-Ordinated Sciences-Concise Summary Notes- All Topics
Circulatory System in Mammals
📌 Introduction
The circulatory system is a transport system made up of:
- Blood vessels → carry blood around the body.
- Heart (pump) → muscular organ that pumps blood.
- Valves → ensure one-way flow of blood.
It transports oxygen, nutrients, hormones and removes wastes (CO₂, urea, etc.).
🔄 Double Circulation
Mammals have a double circulation: blood passes through the heart twice in one complete circuit.
- Pulmonary circulation → Heart → Lungs → Heart
Carries deoxygenated blood from heart to lungs.
Gas exchange → blood becomes oxygenated. - Systemic circulation → Heart → Rest of body → Heart
Carries oxygenated blood to organs/tissues.
Delivers O₂ + glucose, collects CO₂ + wastes.
Advantage: maintains high blood pressure in systemic circulation → fast delivery of oxygen and nutrients to organs.
❤️ Heart as a Pump
- The right side → pumps deoxygenated blood to the lungs (low pressure).
- The left side → pumps oxygenated blood to the body (high pressure, thicker muscle).
- Contractions of ventricles keep blood moving continuously.
🚪 Role of Valves
- Found in heart and veins.
- Function: prevent backflow of blood, ensuring one-way movement.
Types:
- Atrioventricular valves (between atria and ventricles).
- Semilunar valves (in arteries leaving heart).
- Valves in veins (help blood flow upwards against gravity).
🩸 Blood Vessels
- Arteries → carry blood away from heart (high pressure).
- Veins → return blood to heart (with valves).
- Capillaries → very thin walls, allow exchange of materials (O₂, glucose, CO₂, wastes).
Pathway example:
Arteries → Arterioles → Capillaries → Venules → Veins
📝 Summary Table
| Feature | Pulmonary Circulation | Systemic Circulation |
|---|---|---|
| Direction | Heart → Lungs → Heart | Heart → Body → Heart |
| Blood type leaving heart | Deoxygenated | Oxygenated |
| Function | Gas exchange | Transport O₂, nutrients, wastes |
| Pressure | Low | High |
⚡ Quick Recap
Circulatory system = heart + vessels + valves.
Double circulation: Pulmonary (lungs) + Systemic (body).
Valves → one-way flow.
Left ventricle = thick wall → pumps at high pressure to body.
Capillaries → site of exchange.
Single Circulation in Fish
📌 Introduction
Unlike mammals (double circulation), fish have a single circulation.
This means blood passes through the heart only once in each complete circuit of the body.
🔄 Pathway of Blood Flow
- Heart (2 chambers: 1 atrium + 1 ventricle)
Ventricle pumps deoxygenated blood to the gills. - Gills (gas exchange site)
Blood picks up oxygen and releases carbon dioxide.
Now the blood is oxygenated. - Body tissues
Oxygenated blood flows directly to the body organs and tissues.
Oxygen + nutrients supplied, CO₂ + wastes collected. - Back to heart
Deoxygenated blood returns to atrium.
So, the heart → gills → body → heart (single loop).
🫀 Structure of Fish Heart
- 2 chambers only:
- 1 atrium (receives blood).
- 1 ventricle (pumps blood).
- Simple compared to mammalian 4-chambered heart.
Advantages of Single Circulation
Efficient for fish because:
- Fish are cold-blooded (ectothermic) → lower energy demands.
- Water provides support + oxygen supply.
Disadvantage
- Blood loses pressure after passing through gills.
- Flow to body is slower compared to mammals → not suitable for high activity or warm-blooded animals.
📝 Summary Table
| Feature | Fish (Single circulation) | Mammals (Double circulation) |
|---|---|---|
| Heart chambers | 2 (1 atrium, 1 ventricle) | 4 (2 atria, 2 ventricles) |
| Blood passes heart | Once per circuit | Twice per circuit |
| Pressure | Drops after gills → slower flow | Maintains high pressure |
| Adapted for | Cold-blooded, low metabolism | Warm-blooded, high metabolism |
⚡ Quick Recap
Fish heart = 2 chambers (atrium + ventricle).
Blood flow = Heart → Gills → Body → Heart.
Advantage: simple, suits low energy demand.
Disadvantage: slow blood flow due to pressure drop at gills.
Double Circulation in Mammals
📌 Introduction
Mammals have a double circulation system.
This means blood passes through the heart twice in each complete circuit.
Ensures high pressure and fast transport of oxygen + nutrients to body tissues.
🔄 Pathways of Blood Flow
1. Pulmonary Circulation (Heart ↔ Lungs)
- Right side of heart pumps deoxygenated blood → lungs.
- In lungs → blood becomes oxygenated (CO₂ released, O₂ absorbed).
- Oxygenated blood returns to the left atrium.
2. Systemic Circulation (Heart ↔ Body)
- Left side of heart pumps oxygenated blood → rest of the body.
- Body tissues absorb O₂ + nutrients, release CO₂ + wastes.
- Now deoxygenated blood returns to the right atrium.
So, overall route:
Heart → Lungs → Heart → Body → Heart
🫀 Structure of Mammalian Heart
- 4 chambers:
- Right atrium, Right ventricle (deoxygenated side).
- Left atrium, Left ventricle (oxygenated side).
- Valves ensure one-way flow of blood.
✅ Advantages of Double Circulation
- Maintains higher blood pressure in systemic circulation.
- Provides efficient oxygen supply for high metabolism.
- Supports warm-blooded lifestyle → mammals need more energy for body temperature regulation and activity.
📝 Summary Table
| Feature | Fish (Single) | Mammals (Double) |
|---|---|---|
| Heart chambers | 2 (1 atrium, 1 ventricle) | 4 (2 atria, 2 ventricles) |
| Blood passes heart | Once per circuit | Twice per circuit |
| Pressure | Drops after gills | Maintains high pressure |
| Adapted for | Cold-blooded, low energy | Warm-blooded, high energy |
⚡ Quick Recap
Double circulation = blood passes heart twice per circuit.
Two routes:
Pulmonary (heart–lungs–heart)
Systemic (heart–body–heart)
Heart = 4 chambers + valves.
Advantage → high pressure, rapid supply, supports warm-blooded metabolism.
Advantages of Double Circulation in Mammals
📌 Key Idea
In double circulation, blood passes twice through the heart in one circuit.
This system gives mammals big benefits compared to single circulation (like in fish).
✅ Main Advantages
1. Maintains High Blood Pressure in Body (Systemic Circulation)
- Blood going to the body is pumped at high pressure.
- Ensures fast delivery of oxygen and glucose to tissues.
- Helps in quick removal of wastes (CO₂, urea).
2. Efficient Oxygen Supply
- Oxygenated and deoxygenated blood are kept separate (4-chambered heart).
- Tissues always get rich oxygen supply, important for high activity levels.
3. Supports High Metabolism
- Mammals are warm-blooded (endothermic).
- Double circulation provides enough energy for:
- Temperature regulation
- Fast movement, active lifestyle.
4. Improved Gas Exchange
- Pulmonary circulation sends blood to lungs at lower pressure, preventing damage to delicate lung tissues.
- Systemic circulation sends blood at higher pressure for rapid distribution.
📝 At a Glance
| Advantage | Why it matters |
|---|---|
| High pressure to body | Faster delivery of O₂ + nutrients |
| Low pressure to lungs | Protects lung tissues |
| Separation of blood | No mixing → efficient O₂ transport |
| Supports endothermy | Enough energy for warm-blooded lifestyle |
⚡ Quick Recap
Double circulation = blood passes heart twice per circuit.
Pulmonary circulation → lungs (low pressure).
Systemic circulation → body (high pressure).
Advantages: higher efficiency, no mixing of blood, supports high metabolism + endothermy.