Topic 9.4: Blood & Immunity
The River of Life & Your Cellular Army
Blood: The Transport System
Blood is a tissue consisting of plasma containing red blood cells, white blood cells, and platelets.
Red Blood Cells (RBCs)
Haemoglobin: Red protein that binds O₂
No Nucleus: More space for haemoglobin
Biconcave Shape: Large surface area for gas exchange
Function: Transport oxygen from lungs to tissues
Plasma
Yellow Liquid: 55% of blood volume
Transports:
- Blood Cells
- Ions (Na⁺, K⁺, Ca²⁺)
- Nutrients (Glucose, Amino Acids)
- Urea (Waste)
- Hormones
- CO₂
- Heat Energy
Platelets
Cell Fragments: No nucleus
Function: Blood clotting
Prevent blood loss & pathogen entry
White Blood Cells (WBCs)
Phagocyte
Nucleus: Irregular/Lobed
Action: Engulfs & Digests pathogens
Process: Phagocytosis
Lymphocyte
Nucleus: Large & Round
Action: Produces Antibodies
Target: Specific pathogens
Supplement: The Clotting Mechanism
Fibrinogen (Soluble protein in plasma) converts to Fibrin (Insoluble mesh)
Fibrin traps red blood cells to form a clot/scab
Prevents blood loss and pathogen entry
Examiner Traps to Avoid
❌ "White blood cells kill bacteria"
✅ Be specific: Phagocytes engulf and digest OR Lymphocytes produce antibodies
❌ "Blood clots to stop bleeding"
✅ Fibrinogen converts to Fibrin which traps RBCs to form a clot
❌ "Plasma carries oxygen"
✅ Red blood cells (haemoglobin) carry oxygen. Plasma carries CO₂, nutrients, hormones, etc.
❌ "Antibodies destroy pathogens"
✅ Antibodies bind to specific antigens marking them for destruction
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