1) Transmissible Disease
  • ​A pathogen is an organism that causes disease. They include bacteria and viruses.
  • Pathogens can be spread from host to host through contact with an infected organism, or through other mediums such as food, water, waste and bodily fluids, and are thus called transmissible diseases. 
2) State the Body Defences
  • Mechanical barriers:  skin and hair in the nose.
  • Chemical barriers:  stomach acid, mucus produced by the lining of the trachea and bronchi, and tears which contain an enzyme called lysozyme, which can kill bacteria by lysing their cell wall.
  • Cells:  phagocytosis and antibody production by white blood cells.
  • Vaccination:  can enhance the body’s defense.
3) Explain how Antibodies destroy Pathogens
  • Pathogens can be detected by white blood cells and are destroyed in an immune response.
  • Each pathogen has a specific antigen protein on the cell membrane.
  • In an immune response, lymphocytes produce specific antibodies (a protein), which bind to the antigens to produce an antibody-antigen complex, the pathogens are now clumped together making them harmless.
  • They can either be killed or marked, making it easier for the phagocytes to find and ingest them.
  • Each pathogen has its own antigens, which have specific shapes, so specific antibodies which fit the specific shapes of the antigens are needed.
4) Explain Active Immunity
  • Is the defence against a pathogen by antibody production in the body.
  • This is gained after an infection by a pathogen, or by vaccination.
5) Explain the Process of Vaccination
  • Inoculated (vaccinated) by harmless pathogen which has antigens.
  • The antigens trigger an immune response by lymphocytes, which produces the antibodies.
  • Memory cells are produced which stay in the body, give long-term immunity.
6) Explain Role of Vaccination in Controlling Spread of Diseases
  • Vaccination can be used to control the spread of disease by providing herd immunity.
  • This is where a large amount of the population is vaccinated and are thus immune to the pathogen, so the disease cannot spread as there are only a few people left who can still become infected.
  • The few that cannot be vaccinated, for example due to medical reasons, are therefore protected against the disease.
7) Importance of Hygienic Food Preparation
  • Good personal hygiene, waste disposal and sewage treatment are important in controlling the spread of disease.
8) Explain Passive Immunity
  • Is a short-term defence against a pathogen by antibodies acquired from another individual.
  • One example of passive immunity is antibodies being passed to a baby through the mother’s milk, thus it is important for babies to be breastfed to reduce the risk of diseases.
  • This is short-term as no memory cells are formed.
  • A baby’s immune responses are not yet fully developed, so when a mother breastfeeds her baby, the milk which contains the mother’s white blood cells produces antibodies and provide the baby with protection against infection.
9) Diseases caused by the Immune System
  • Example is Type 1 diabetes.
  • Inability of islet cells in the pancreas to produce sufficient insulin, so a virus infection can cause the body’s immune system to attack the islet cells that produce insulin. This is classed as an autoimmune.
  • The outcome is that the patient’s blood is deficient in insulin and he/she needs regular injections of the hormone in order to control blood sugar levels and so lead a normal life.