Blood

• How are Red blood cells specially adapted cells to carry oxygen to the cells and carbon dioxide away from the cells to the lungs?

  • They have haemoglobin, which binds to oxygen to create oxyhaemoglobin
  • They have no nucleus which leaves more room for haemoglobin to be packed in
  • They have a biconcave shape, they are described as being a ‘biconcave disk’, which increases the surface area to volume ratio to maximise diffusion in and out of the cell
• What percentage of blood do White blood cells make up?

  <1%
• what are the two main types of white blood cells?

  lymphocytes and phagocytes
• what percentage of white blood cells do lymphocytes make up?

  around 25%
• What two things do lymphocytes produce?

  antibodies and antitoxins
• why do lymphocytes produce anti bodies?

  to destroy pathogenic cells
• why do lymphocytes produce antitoxins?

  to neutralise toxins released by the pathogens
• what other two things can lymphocytes also do?

  • produce marker molecules to ‘mark’ pathogens as foreign for phagocytes to recognise
  • cause pathogens to stick together, making the phagocytosis more effective.
• How can lymphocytes be easily recognised under the microscope?

  • large round nucleus which takes up nearly the whole cell
  • clear, non-granular cytoplasm
• Why do lymphocytes have well developed machinery?

  to produce a large number of cells quickly in response to an infection by pathogens
• what percentage of blood do red blood cells make up?

  around 55%
• what percentage of white blood cells do phagocytes make up?

  around 75%
• how do phagocytes carry out phagocytosis?

  by engulfing and releasing digestive enzymes to digest pathogens
• How do phagocytes know if it is a pathogen?

  they have a sensitive cell membrane that can detect chemicals given off by pathogenic cells
• how can phagocytes be recognised under the microscope?

  • multi-lobed nucleus which allows the phagocyte to change shape easily
  • granular cytoplasm
• what are platelets?


  they are fragments of cells that are involved in blood clotting and formation of scabs
• when the skin is broken what series of reactions take place within the plasma?

  • Platelets release chemicals that cause soluble fibrinogen proteins to convert into insoluble fibrin and form an insoluble mesh across the wound, trapping red blood cells and therefore forming a clot.
  • The clot eventually dries and develops to form a scab to protect the wound from bacteria entering.
• why is blood clotting important?

  • It prevents continued/significant blood loss from wounds
  • Scab formation seals the wound with an insoluble patch that prevents entry of microorganisms that could cause an infection.
  • The scab stays in place until new skin has grown underneath it, sealing the skin again.