CIE iGCSE Biology-9.4 Blood- Study Notes- New Syllabus
CIE iGCSE Biology-9.4 Blood- Study Notes – New syllabus
CIE iGCSE Biology-9.4 Blood- Study Notes -CIE iGCSE Biology – per latest Syllabus.
Key Concepts:
Core
- List the components of blood as: red blood cells, white blood cells, platelets and plasma
- Identify red and white blood cells in photomicrographs and diagrams
- State the functions of the following components of blood:
(a) red blood cells in transporting oxygen, including the role of haemoglobin
(b) white blood cells in phagocytosis and antibody production
(c) platelets in clotting (details are not required)
(d) plasma in the transport of blood cells, ions, nutrients, urea, hormones and carbon dioxide - State the roles of blood clotting as preventing blood loss and the entry of pathogens
Supplement
- Identify lymphocytes and phagocytes in photomicrographs and diagrams
- State the functions of:
(a) lymphocytes – antibody production
(b) phagocytes – engulfing pathogens by phagocytosis - Describe the process of clotting as the conversion of fibrinogen to fibrin to form a mesh
Components of Blood
Blood is a specialized fluid that circulates through the body, transporting substances and defending against disease. It is made up of four main components, each with a specific function.
1. Red Blood Cells (RBCs)
Also known as erythrocytes
- Function: Carry oxygen from the lungs to tissues and transport carbon dioxide back to the lungs.
- Structure:
- Biconcave shape – increases surface area for gas exchange
- No nucleus – more space for haemoglobin
- Contains: Haemoglobin – the red pigment that binds oxygen
📌 Note: Red blood cells make up about 45% of blood volume.
2. White Blood Cells (WBCs)
Also known as leukocytes
- Function: Defend the body against infections, pathogens, and foreign substances.
- Types:
- Phagocytes – engulf and digest microbes
- Lymphocytes – produce antibodies
- Structure: Larger than RBCs, and have a nucleus
📌 Note: Fewer in number than RBCs, but crucial for immunity.
3. Platelets
Also known as thrombocytes
- Function: Help in blood clotting to prevent bleeding after injury.
- Structure: Tiny cell fragments with no nucleus.
- Action: Clump to form clots and release chemicals that activate clotting.
📌 Note: Without platelets, even small cuts could be dangerous.
4. Plasma
- Function: Straw-colored liquid that carries all components of blood.
- Carries:
- Nutrients (e.g., glucose, amino acids)
- Hormones, antibodies, carbon dioxide (as bicarbonate ions)
- Waste products like urea
- Makes up: About 55% of blood volume
📌 Note: Plasma is the transport medium of the bloodstream.
🧠 Quick Recap Table
| Component | Function | Key Features |
|---|---|---|
| Red Blood Cells | Transport oxygen and carbon dioxide | Biconcave, no nucleus, contains haemoglobin |
| White Blood Cells | Defend against infection | Have nucleus, different types |
| Platelets | Help in blood clotting | Cell fragments, no nucleus |
| Plasma | Transport medium | Liquid portion, carries many substances |
Identifying Red and White Blood Cells in Photomicrographs and Diagrams
Red Blood Cells (RBCs) – Erythrocytes
🧠 Key Identification Features:
| Feature | Description |
|---|---|
| Shape | Round and biconcave (doughnut-shaped without a hole) |
| Size | Smaller than white blood cells |
| Color (in photomicrographs) | Appear pink or light red (due to staining) |
| Nucleus | No nucleus – more room for haemoglobin |
| Arrangement | Seen in large numbers, often forming chains or clusters |
✅ Tip: RBCs are the most numerous cells and appear smooth and uniform in shape.
White Blood Cells (WBCs) – Leukocytes
🧠 Key Identification Features:
| Feature | Description |
|---|---|
| Shape | Irregular or rounded – varies by type |
| Size | Larger than red blood cells |
| Color (in photomicrographs) | Usually stained purple or dark blue |
| Nucleus | Present – often large and dark, sometimes lobed |
| Quantity | Fewer than RBCs – scattered throughout the image |
✅ Tip: WBCs appear darker, larger, and are fewer. Look for distinct nuclei or lobed shapes.
🔍 Visual Summary
| Cell Type | Shape & Size | Nucleus | Color in Stains | Frequency in Image |
|---|---|---|---|---|
| Red Blood Cell | Small, biconcave disc | Absent | Pink/red (pale center) | Very numerous |
| White Blood Cell | Large, round/irregular | Present | Dark purple/blue | Few and scattered |
Functions of the Components of Blood
🩸 (a) Red Blood Cells (RBCs) – Transport of Oxygen
Red blood cells are specialized for transporting oxygen from the lungs to all body tissues.
- Contain haemoglobin, a red iron-rich pigment that binds to oxygen.
- In the lungs, haemoglobin forms oxyhaemoglobin.
- In tissues, oxygen is released for respiration.
- No nucleus – more space for haemoglobin.
- Biconcave shape – increases surface area for efficient gas exchange.
RBCs transport oxygen efficiently due to haemoglobin and their unique shape.
🛡️ (b) White Blood Cells (WBCs) – Defence and Immunity
White blood cells protect the body from infections using two major methods:
- Phagocytosis: Phagocytes engulf and digest microbes like bacteria – acting as the body’s internal “cleaners”.
- Antibody Production: Lymphocytes detect antigens and produce antibodies to destroy pathogens. Some form memory cells for long-term immunity.
WBCs defend the body via phagocytosis and antibody production.
🩹 (c) Platelets – Blood Clotting
Platelets are tiny fragments of cells that help seal wounds.
- Trigger a chemical reaction that leads to blood clot formation.
- Prevent excess blood loss and entry of pathogens.
Platelets are essential for sealing wounds and preventing infection.
💧 (d) Plasma – Transport Medium
Plasma is the pale yellow liquid that makes up about 55% of blood. It carries many substances:
| Substance | Purpose |
|---|---|
| Blood cells | Suspends and transports RBCs, WBCs, and platelets |
| Ions (e.g. Na⁺, Cl⁻) | Maintains pH and ionic balance |
| Nutrients | Glucose, amino acids, fatty acids for cells |
| Urea | Waste taken to kidneys for removal |
| Hormones | Carries signals like insulin, adrenaline |
| Carbon dioxide | Transported to lungs for exhalation |
Plasma acts as a transport highway, carrying essential substances around the body.
Role of Blood Clotting: Preventing Blood Loss and Entry of Pathogens
🔐 1. Preventing Blood Loss
- Platelets gather at the site and form a temporary plug.
- A chemical reaction causes fibrin threads to form a mesh.
- This mesh traps blood cells and creates a clot (scab).
- The clot seals the wound and stops further bleeding.
Prevents excessive blood loss, which can reduce oxygen supply to vital organs and become life-threatening.
🛡️ 2. Preventing Entry of Pathogens
- Open wounds can allow bacteria or viruses to enter the body.
- A blood clot forms a barrier that blocks microbes from entering.
Protects the body from harmful pathogens that can cause diseases.
📝 Summary Table:
| Role | Description |
|---|---|
| Prevent blood loss | Forms clots to stop bleeding at injury sites |
| Prevent infection | Blocks the entry of microbes through broken skin |
Identifying Lymphocytes and Phagocytes in Photomicrographs
Understanding the two main types of white blood cells (WBCs) – lymphocytes and phagocytes – is essential for recognizing them in microscope images and diagrams.
🧫 1. Phagocytes
Also known as macrophages or neutrophils, these cells engulf and digest pathogens.
Key Features:
- Lobed nucleus (usually 2–5 lobes)
- Granular cytoplasm
- Larger than lymphocytes
- Irregular shape (especially during phagocytosis)
In Photomicrographs:
- Large cells with segmented/lobed nuclei
- Granules may be visible in cytoplasm
- Often seen near or engulfing microbes
🧬 2. Lymphocytes
These WBCs are key players in antibody production and immune memory.
Key Features:
- Large, round nucleus occupying most of the cell
- Very little cytoplasm visible
- Smooth and regular shape
- Smaller than phagocytes
In Photomicrographs:
- Appear small with dense, round nucleus
- Minimal pale cytoplasm around nucleus
- Look compact and uniform
🔍 Quick ID Tip
If you see a large WBC with a lobed nucleus and grainy cytoplasm, it’s likely a phagocyte.
A small WBC with a big round nucleus and minimal cytoplasm is probably a lymphocyte.
🔍 Comparison Table:
| Feature | Phagocyte | Lymphocyte |
|---|---|---|
| Nucleus shape | Lobed or segmented | Large and round |
| Size | Larger | Smaller |
| Cytoplasm | Granular, visible | Very little |
| Function | Phagocytosis | Antibody production |
| Appearance | Irregular shape | Smooth, round |
Functions of White Blood Cells
White blood cells (WBCs) are part of the body’s immune system, defending it against infections and disease. There are two main types to focus on:
(a) Lymphocytes – Antibody Production
Function: Lymphocytes produce antibodies.
- Each lymphocyte targets one specific antigen.
- When it detects a pathogen, it produces antibodies that bind to that antigen.
- This neutralizes or marks the pathogen for destruction.
- Some lymphocytes become memory cells for long-term immunity.
(b) Phagocytes – Engulfing Pathogens by Phagocytosis
Function: Phagocytes engulf and digest pathogens.
- Phagocyte attaches to the pathogen.
- It surrounds and engulfs it (like Pac-Man).
- Uses enzymes to break it down inside the cell.
- Clears harmful microbes from blood and tissues.
Lymphocytes = Long-term defense via antibody production.
Phagocytes = Pac-Man style pathogen eaters that digest invaders.
Blood Clotting: Fibrinogen to Fibrin
Blood clotting is a vital process that prevents excessive bleeding and protects the body by sealing wounds and blocking pathogen entry.
What Triggers Clotting?
- Damage to skin or blood vessel activates platelets.
- Clotting factors in plasma are released, starting a cascade.
Key Steps in the Clotting Process
1. Activation of Clotting Factors
- Injury triggers release of clotting factors.
- These initiate a chain reaction leading to fibrin production.
2. Conversion of Fibrinogen to Fibrin
- Fibrinogen (soluble plasma protein) is converted to fibrin.
- This reaction is catalysed by the enzyme thrombin.
3. Formation of a Fibrin Mesh
- Fibrin forms insoluble threads across the wound site.
- This traps red blood cells and platelets – forming a clot.
4. Sealing the Wound
- The clot hardens into a scab.
- Prevents blood loss and protects against microbes.
✅ Summary:
Fibrinogen (soluble) → Fibrin (insoluble) → Mesh → Clot → Scab
| Term | Meaning |
|---|---|
| Fibrinogen | Soluble protein in plasma (inactive) |
| Fibrin | Insoluble protein that forms mesh threads |
| Thrombin | Enzyme that converts fibrinogen to fibrin |
Clotting prevents blood loss
& blocks pathogen entry into wounds.