Edexcel iGCSE Biology-3.9 The Blood- Study Notes- New Syllabus

Composition of Blood

📌 Introduction

Blood is a transport fluid that delivers oxygen, nutrients, and hormones while removing wastes.
It also plays a role in defence, clotting, and temperature regulation.
Main components: plasma, red blood cells, white blood cells, platelets.

🔴 Red Blood Cells (RBCs / Erythrocytes)

• Shape: Biconcave discs → increase surface area for gas exchange.
• Nucleus: No nucleus → more space for haemoglobin.
• Content: Packed with haemoglobin → binds oxygen to form oxyhaemoglobin.
• Function: Transport oxygen from lungs → body tissues.
• Adaptation: Small and flexible → can pass through narrow capillaries.

⚪ White Blood Cells (WBCs / Leucocytes)

General role: Defend body against pathogens.

Two main types:

• Phagocytes:
  Engulf and digest bacteria/viruses.
  Use enzymes to destroy pathogens.
  Called “non-specific defence”.
• Lymphocytes:
  Produce antibodies → attach to antigens on pathogens.
  Produce memory cells → immunity after infection/vaccination.
  Specific to each pathogen.

🟡 Platelets (Thrombocytes)

• Small fragments of cells (not full cells).
• Function: Help in blood clotting.
• Release chemicals → form a mesh of fibrin.
• Stops bleeding and prevents entry of pathogens.

🟠 Plasma

• Liquid part of blood (yellowish fluid).
• Makes up ~55% of blood volume.
• Transports:
  • Nutrients (glucose, amino acids, lipids).
  • Waste products (urea, CO₂).
  • Hormones & antibodies.
  • Heat → helps maintain body temperature.

📊 Summary Table

⚡ Quick Recap
RBCs → oxygen carriers (haemoglobin, biconcave, no nucleus).
WBCs → defence (phagocytes = engulf, lymphocytes = antibodies).
Platelets → clot blood, prevent pathogen entry.
Plasma → transport medium (nutrients, wastes, hormones, heat).