Circulatory system- blood

• Red blood cells

  • to carry oxygen from lungs
  • have disc shape to give large surface area for absorbing O2
  • no nucleus - allows more room to carry oxygen
  • contain red pigment called haemoglobin
• White blood cells

  • defend against infection
  • change shape to kill microorganisms this is called phagocytosis
  • produce antibodies to fight microorganisms and produce antitoxins to neutralise any toxins produced by microorganisms
  • do have nucleus
• Platelets

  • small fragments of cells- no nucleus
  • help blood to clot at a wound- to stop blood pouring and stop microorganisms getting in
  • lack of platelets can cause excessive bleeding and bruising
• Plasma carries;

  • red, white blood cells and platelets
  • nutrients like glucose and amino acids
  • carbon dioxide form organs to lungs
  • urea from liver to kidneys
  • hormones
  • proteins
  • antibodies and antitoxins produced by white blood cells