Infection and Response

• What is a communicable disease?

  Any disease that is infectious.
• What are communicable diseases caused by?

  Viruses, bacteria, protists and fungi all cause infections in animals and plants, and these infections can be spread from one individual to another.
• What is a pathogen?

  Any virus, bacteria, protist or fungus that causes an infectious disease. They are all microorganisms.
• Do all microorganisms cause infectious disease?

  No, many microorganisms are not pathogens. Some bacteria are useful, for making cheese and yoghurt. We eat some fungi, like mushrooms and Quorn.
• What do pathogenic bacteria do?

  Their cells reproduce rapidly inside the body, producing toxins that damage tissues and make us feel ill.
• What is salmonella?

  A type of food poisoning caused by bacteria ingested (eaten) in/on food (usually chicken or egg) that has been prepared in unhygenic conditions.
• What are the symptoms of salmonella?

  Fever, abdominal cramps, vomiting and diarrhoea are caused by the salmonella bacteria and the toxins they release.
• How are we kept safe from salmonella?

  In the UK chickens are vaccinated against salmonella to control the spread of bacteria. People are encouraged to take care preparing chicken.
• What is gonorrhoea?

  A sexually transmitted disease (STD) caused by bacteria. It is spread by sexual contact with an infected person.
• What are the symptoms of gonorrhoea?

  Thick yellow or green discharge from the penis or vagina, and pain when urinating.
• What can we use to treat gonorrhoea?

  The antibiotic penicillin worked well to treat gonorrhoea until resistant strains of bacteria evolved. Now scientists are researching to develop new treatments.
• How can we prevent gonorrhoea spreading?

  Antibiotics will kill the bacteria, but the infected person needs to use a barrier method of contraception eg condom.
• What do pathogenic viruses do?

  They reproduce rapidly inside cells, causing cell damage when they are released.
• What is measles?

  A viral disease that is serious and can cause death if the infected person suffers from complications. It is spread by inhaling droplets from sneezes and coughs.
• What are the symptoms of measles?

  A red skin rash and fever.
• How can we prevent measles spreading?

  Most young children are vaccinated against measles.
• What is HIV?


  A viral disease that attacks the body's immune cells. It is spread by sexual contact or exchange of body fluids such as blood (eg. when drug users share needles).
• What are the first symptoms of HIV?

  A flu-like illness is the first symptom. If successfully controlled, the virus doesn't attack the body's immune cells.
• What is late stage HIV (AIDS)?

  In late stage HIV, the immune system becomes seriously damaged and the infected person gets ill from any other infections eg. colds or flu, and sometimes cancers.
• How can we treat HIV?

  Medicines called antiretroviral drugs can successfully control the virus and prevent some of the damage to the immune system. This can stop HIV becoming AIDS.
• What is Tobacco Mosaic Virus (TMV)?

  This is a virus that infects and damages many plant species including tomato.
• What are the symptoms of Tobacco Mosaic Virus?

  A "mosaic" coloured pattern appears on the leaves. The pattern ranges from paler green, to yellow or brown. It affects plant growth as less photosynthesis occurs.
• What are the symptoms of rose black spot?

  Purple or black spots appear on leaves. The leaves often turn yellow and fall off the plant. It affects plant growth as there are fewer leaves to photosynthesise.
• How can we treat rose black spot?

  Fungicide sprays can be used, and removing (and destroying) the affected leaves also helps prevent the spread of the fungus to other leaves and other plants.
• What is malaria?

  A disease caused by a protist. The protist is spread by biting mosquitos as the protist is a parasite that lives in the mosquito for part of it's life cycle.
• What are the symptoms of malaria?

  A fever and flu-like symptoms that recur every few days. The most common malaria infections cause fever every three or every four days and can be fatal.
• What is a vector species?

  A vector is a species that carries a microorganism from one infected individual to another. In malaria, the mosquito is the vector.
• How can we prevent the spread of malaria?

  Preventing the vector from spreading the protist, using mosquito nets to avoid being bitten. Preventing the mosquitos from breeding keeps vector numbers low.
• What are non-specific defence systems?

  Defences that the body has against all types of pathogens. These include, skin, nose, trachea, bronchi and stomach.
• How does the skin prevent pathogens entering?

  The skin is a waterproof layer that prevents most pathogens from entering the body. If the skin is damaged, the wound is sealed quickly by a scab forming.
• How does the nose prevent pathogens entering?

  The nose has hairs and mucus to trap airborne pathogenic microorganisms and stop them from getting further into the body.
• How do the trachea/bronchi prevent pathogens entering?

  They have sticky mucus that traps airborne pathogens, and also the cells lining these airways have cilia that waft the mucus up to the throat to be swallowed.
• How does the stomach prevent pathogens entering?

  The stomach contains hydrochloric acid (pH2) which destroys most pathogens that are ingested in food.
• What exactly do white blood cells do?

  They carry out phagocytosis, as well as producing antibodies and antitoxins.
• What is phagocytosis?


  When a white blood cell engulfs a bacteria and then destroys it by digesting it using enzymes.
• What are antitoxins?

  Chemicals produced by white blood cells that neutralise the toxins produced by bacteria. The toxins are one of the reasons why we feel ill.
• What are antibodies?

  Specific shaped molecules that can bind onto a particular pathogen so that it can be destroyed.
• How can we become immune to an infectious disease?

  The first time a white blood cell meets a pathogen, it takes time to make antibodies to destroy it. The next time that pathogen enters, antibodies can be made fast so we don't get ill.
• What is a vaccine?

  A small quantity of a dead or inactive form of a pathogen that can be put into an individual so that they can develop immunity to the pathogen.
• How do vaccinations work?

  When a white blood cell meets the dead/inactive pathogen it reacts as if it is harmful, and produces antibodies. These antibodies can then be made quickly in future.