Blood Cells (AQA GCSE Combined Science: Synergy: Life & Environmental Sciences): Revision Note

Components of Blood

What is blood?

• The role of blood in the body is to transport useful substances to every cell of the body, and to remove harmful waste substances

  • It also plays a vital role in transferring heat from “active” organs to cooler parts of the body (such as the extremities – hands and feet)

• Blood is a tissue consisting of the fluid plasma (which is largely water with dissolved substances in it)

• Red blood cells, white blood cells and platelets are suspended in blood plasma

 Structure of the blood diagram

Red blood cells

• Red blood cells (RBCs) are cells with a distinctive biconcave disc shape

• This shape is a result of RBCs not having a nucleus

  • The biconcave shape gives RBCs a large surface to volume ratio; this is a key adaptation to maximise the efficiency of diffusion of gases into and out of the cell

• The cytoplasm of an RBC is packed with the protein haemoglobin

• Oxygen binds reversibly with haemoglobin, forming the red pigment oxyhaemoglobin:

  • oxygen + haemoglobin ⇌ oxyhaemoglobin

White blood cells

• White blood cells (WBCs) are part of the immune system, responsible for defending the body from infection by recognising and destroying pathogens

• WBCs defend the body in three particular ways:

  • Phagocytes engulf and digest pathogens, destroying them

  • Lymphocytes produce specific antibodies that help enhance phagocyte activity by sticking them together (clumping) or disabling pathogens

  • Some lymphocytes produce a type of antibody called an antitoxin which is able to bind to toxic substances produced by pathogens, neutralising them

• WBCs have a variety of adaptations:

  • Phagocytes have a lobed nucleus and are autonomous - they leave the blood and patrol the tissues

  • Lymphocytes have a large nucleus and can produce antibodies extremely quickly

Platelets

• Platelets are fragments of cells (they contain cytoplasm but no nucleus)

• When damage to a blood vessel occurs, the platelets are involved in forming a blood clot to prevent blood loss

• Individuals with insufficient platelets cannot clot their blood effectively – this can be life-threatening if excessive damage occurs