exam questions

• Types of barriers (2)

  -       Keratin in the skin= physical 

  -       Lysozyme in mucus= chemical 

  -       HCL in stomach= chemical
• Explain how changes in the blood vessels result in redness and swelling at site of inflammation (4)

  -       Histamine released by body cells causes vasodilation of arterioles

  -       More blood flows through capillaries to the site of infection, causing redness 

  -       Histamine causes capillary walls to be more permeable 

  -       Allowing blood plasma to leave capillaries and enter tissue causing swelling
• Explain why the presence of microorganism on the skin and in the gut helps to prevent pathogenic organisms multiplying in the body (3)

  -       Flora in the gut and skin are better adapted to the conditions 

  -       Therefore, they can outcompete pathogenic organisms 

  -       Bacteria in the gut secrete chemicals which help to destroy pathogens
• Explain why there are relatively few species of bacteria in the stomach (2)

  -       HCL in stomach creates acidic conditions/ low PH- causing bacterial enzymes to denature

  -       Bacteria that live in the stomach have adaptions that enable them to survive 
• Describe how pathogens are destroyed by phagocytosis when they enter the human body (4)

  -       Chemicals eg histamine attract phagocytes to the area 

  -       Phagocyte recognises a non-self-antigen

  -       Phagocytes extend out their cell membrane around the pathogen, trapping it in a phagocytic vacuole via endocytosis 

  -       Enzymes released into vacuole when it fuses with lysozymes, including lysozyme enzyme 

  -       Enzymes digest the pathogen=antigen presenting cell 

  -       This triggers a specific immune response to kill the APC
• State 2 characteristic features of antibodies (2) 

  -       2 heavy polypeptide chains and 2 light polypeptide chains 

  -       Hinge region and chains joined by disulphide bonds 

  -       Variable region on each chain and a constant region 
• Describe how the production and action of interferon differs from the production and action of lysozyme (3) 

  -       Interferons involved in viral infections 

  -       Lysozymes affects bacteria 

  -       Interferons produced by infected cells and lysozyme present in phagocytes 

  -       Interferons inhibit replication of viruses whereas lysozyme kills bacteria via damage to cell wall=bursting or lysis
• Suggest why the protein structure of lysozyme is important to the way in which is acts against pathogens (4)

  -       lysozyme is an enzyme

  -       enzymes active sites have a specific shape to bacteria 

  -       lysozyme acts on cell wall of bacteria causing bursting/ lysis
• Explain why an insect bite, which breaks surface of skin, may lead to inflammation around the injury (3) 

  -       Damaged tissue, body cells release histamine

  -       Arterioles vasodilate causing more blood to flow through capillaries 

  -       Increased permeability of capillaries so more blood plasma enters tissue causing swelling
• Explain how skin flora protects the body from infection (2)

  -       Skin flora better adapted than pathogens so outcompete for resources eg space and water

  -       Prevents growth/ kills pathogens 

  -       Also released enzymes/chemicals to kill pathogens
• Suggest why a common cold virus cannot infect cells if they enter the blood through a cut in the skin (2) 

  -       There will be a destruction of viruses by phagocytes in phagocytosis process 

  -       Viruses only attach to specific receptors on host cells 

  -       Receptors are not present on blood cells