CIE iGCSE Biology-9.1 Circulatory systems- Study Notes- New Syllabus
CIE iGCSE Biology-9.1 Circulatory systems- Study Notes – New syllabus
CIE iGCSE Biology-9.1 Circulatory systems- Study Notes -CIE iGCSE Biology – 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
Supplement
- Describe the single circulation of a fish
- Describe the double circulation of a mammal
- Explain the advantages of a double circulation
Circulatory System: Blood Vessels, Pump & Valves
The circulatory system is like a delivery and drainage network in your body. It keeps blood flowing in one direction, ensuring that oxygen, nutrients, and waste materials are transported efficiently to where they’re needed.
🚚 What Is the Circulatory System?
The circulatory system is made up of:
- A pump → the heart
- A system of tubes → the blood vessels
- Valves → to ensure the blood flows only one way
Together, these parts create a closed loop that keeps blood circulating continuously throughout the body.
❤️ The Pump: The Heart
The heart is a muscular organ that acts as a double pump:
- Contracts rhythmically, pushing blood into the vessels
- Right side: sends blood to the lungs for oxygen
- Left side: sends oxygen-rich blood to the body
🩸 The Blood Vessels: Pathways for Flow
| Vessel Type | Function | Structure |
|---|---|---|
| Arteries | Carry blood away from the heart | Thick walls, narrow lumen, high pressure |
| Veins | Carry blood towards the heart | Thinner walls, wide lumen, valves present |
| Capillaries | Allow exchange of gases/nutrients | Very thin walls (one cell thick), tiny |
🔁 The Role of Valves
- Found mainly in veins and in the heart
- Work like one-way gates that prevent backflow
- Ensure blood moves in the correct direction
- Crucial in legs, where blood travels upward against gravity
🧠 Why Is One-Way Flow Important?
- Prevents mixing of oxygenated and deoxygenated blood
- Ensures efficient delivery of nutrients and oxygen
- Maintains steady circulation, even with posture changes
- Prevents pooling or backflow in low-pressure veins
🩺 Quick Recap
The circulatory system is a closed system with:
- The heart (pump)
- Blood vessels (tubes)
- Valves (checkpoints)
It ensures that blood flows in one direction, delivering essential substances and maintaining homeostasis.
Single Circulation in a Fish
Fish have a single circulatory system, meaning blood passes through the heart only once during each complete body circuit. This differs from double circulation in mammals.
💓 How It Works:
Heart → Gills → Body → Heart
- The heart pumps deoxygenated blood to the gills.
- In the gills, gas exchange occurs – oxygen enters, CO₂ exits.
- Oxygenated blood flows directly to the body.
- After delivering oxygen, the blood returns deoxygenated to the heart.
🫀 The Fish Heart
Fish have a 2-chambered heart:
- 1 atrium – receives blood
- 1 ventricle – pumps blood out
This simple design supports one-way blood flow.
What Happens in the Gills?
The gills are the fish’s respiratory organs. Blood flows through delicate filaments where:
- Oxygen diffuses in from water
- Carbon dioxide diffuses out into water
🧪 Key Features of Single Circulation
| Feature | Description |
|---|---|
| Heart Chambers | 1 atrium + 1 ventricle |
| Number of Circuits | 1 per heartbeat |
| Gas Exchange Site | Gills |
| Blood Pressure | Drops after gills, slower flow to body |
| Efficiency | Lower than mammals, but sufficient for fish |
🔬 Why Is It Enough for Fish?
Fish are cold-blooded (ectothermic), so their oxygen needs are lower.
Slower blood flow is sufficient for their lower metabolism.
Simple systems need less energy and complexity to sustain.
🎯 Summary
In single circulation, the heart pumps blood to the gills for oxygen, and that same oxygenated blood travels to the body before returning. It’s simple, low-pressure, and ideal for fish.
Double Circulation in Mammals
Mammals, including humans, have a double circulatory system. This means blood passes through the heart twice during each complete journey around the body.
🔄 What Does Double Circulation Mean?
Double circulation has two loops:
| Circulation Loop | Direction | Purpose |
|---|---|---|
| Pulmonary Circulation | Heart → Lungs → Heart | To oxygenate the blood |
| Systemic Circulation | Heart → Body → Heart | To deliver oxygen and nutrients |
Route of Blood Flow
Pulmonary Circulation:
- The right side of the heart receives deoxygenated blood from the body.
- It pumps the blood to the lungs to release CO₂ and absorb oxygen.
- The oxygenated blood returns to the left side of the heart.
Systemic Circulation:
- The left side of the heart pumps oxygen-rich blood to the rest of the body.
- After delivering oxygen, the blood becomes deoxygenated and returns to the right side.
💡 Key Features of Double Circulation
| Feature | Description |
|---|---|
| Heart Chambers | 4 (2 atria + 2 ventricles) |
| Oxygenated & Deoxygenated Blood | Kept completely separate |
| Efficiency | High – supports high energy needs |
| Pressure | High in systemic, low in pulmonary circuit |
🔍 Why Is Double Circulation Important?
- Prevents mixing of oxygenated and deoxygenated blood.
- Ensures efficient oxygen delivery to cells for respiration.
- Maintains high pressure in systemic circulation for quick delivery.
- Protects delicate lung tissue with low-pressure pulmonary flow.
- Supports warm-blooded lifestyle and high metabolic rate.
🧠 Summary
In mammals, double circulation ensures blood flows through the heart twice – once to pick up oxygen in the lungs, and once to deliver it to the body. It’s a highly efficient system that keeps cells well-supplied and functioning.
Advantages of Double Circulation in Mammals
Double circulation is a more advanced and efficient circulatory system found in mammals and birds. It keeps oxygenated and deoxygenated blood separate, allowing the body to function at high metabolic rates.
🔄 What is Double Circulation?
It means blood passes through the heart twice in one complete cycle:
- Pulmonary circulation – heart → lungs → heart (for gas exchange)
- Systemic circulation – heart → body → heart (to supply oxygen & nutrients)
Key Advantages of Double Circulation
| Advantage | Explanation |
|---|---|
| Efficient Oxygen Delivery | Oxygen-rich blood is pumped at high pressure to the body, ensuring all tissues receive enough oxygen quickly. |
| Separation of Blood | Oxygenated and deoxygenated blood remain completely separate for maximum efficiency in gas exchange and energy supply. |
| Higher Blood Pressure (Systemic) | The left ventricle pumps blood at high pressure so oxygen can reach even distant parts of the body. |
| Lower Pressure (Pulmonary) | The right-side pumps blood at low pressure to protect delicate lung tissues during gas exchange. |
| Supports Warm-Blooded Lifestyle | Mammals need a constant body temperature and high energy. Double circulation meets these demands efficiently. |
| Faster Removal of Waste | Carbon dioxide and other wastes are removed more rapidly thanks to an efficient and continuous circulation system. |
🧠 In Simple Words