Exam q

• Explain why the presence of microorganisms on the skin and gut help to prevent pathogens from multiplying

  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 destroy pathogens
• Explain why the destruction of T helper cells causes the symptoms of AIDS.

  lack of T helper cells reduces cytokine production

  therefore a reduction in activation of B cells

  this causes a decrease in antibody production

  this weakens the immune system, increasing risk of infection
• Suggest why treatment with antibiotics may not be effective against the dormant bacteria in the tubercles.

  bacteria are inside macrophages therefore bacteria is not accessible to the antibiotics.
• State two characteristic features of antibodies

  have a antigen binding site

  contain a disulphide bridge