Biology Grade 7: Blood Components

Blood Components

• Blood is a liquid tissue consisting of four main components: plasma, red blood cells, white blood cells, and platelets.
• Blood circulates within blood vessels and can clot if vessels rupture, preventing blood loss.

Plasma

• Comprises about 55% of blood, appearing as a pale yellow fluid.
• Contains 90-95% water with 5-10% consisting of dissolved substances.
• Dissolved substances include:
  • Nutrients: glucose, amino acids, vitamins, mineral ions.
  • Waste products: carbon dioxide, urea.
  • Clotting proteins: prothrombin and fibrinogen.
  • Protective proteins: antibodies.
  • Various hormones.

Red Blood Cells (RBCs)

• The most numerous cells in blood, with 3-5 million RBCs per drop.
• Produced in bone marrow and specialized for oxygen transport.
• Features:
  • Biconcave disc shape for larger surface area to absorb more oxygen.
  • Lack of nucleus provides space for hemoglobin.
  • Hemoglobin binds with oxygen to form oxyhemoglobin, which is transported to body cells.
  • Flexible membranes allow them to navigate narrow capillaries.

White Blood Cells (WBCs)

• Integral to the immune system, defending against infections caused by pathogens.
• Major types include phagocytes and lymphocytes.

Phagocytes

• Engulf and digest pathogens through a process called phagocytosis.
• Have a lobed nucleus and irregular shape.

Lymphocytes

• Produce and secrete antibodies to target and destroy pathogens.
• Characterized by a large round nucleus that occupies most of the cell.

Platelets

• Fragments of cells involved in blood clotting.
• Activate upon skin injury to halt bleeding by forming a clot.
• Release chemicals converting soluble fibrinogen into insoluble fibrin, creating a mesh to trap RBCs and form a clot.
• The clot dries, forming a scab that prevents blood loss and serves as a barrier against pathogens.