Infection and Response

• The immune system is made up of cells, tissues, organs, and proteins that work together to defend the body against infection.
• Virus


  A non-living infectious agent that invades and then replicates inside living cells
• Bacteria


  A single-celled organism that lacks a nucleus and is capable of causing disease
• Protist


  A eukaryotic organism that cannot be classified as an animal, plant or fungus
• Fungi

  An organism that absorbs nutrients from the environment
• Pathogen

  A microscopic organism or virus that causes a disease
• Toxin

  A poison that is harmful to organisms and is produced by pathogens such as bacteria
• Measles

  A virus spread by droplets, causing a red skin rash and a fever which may lead to pneumonia or encephalitis
• Human immunodeficiency virus (HIV)

  A virus with flu-like symptoms that is spread by the exchange of bodily fluids and can lead to AIDS
• Acquired immunodeficiency syndrome (AIDS)


  A disease in which the immune system is severely weakened and cannot fight infection
• Tobacco mosaic virus


  A plant virus which causes a mosaic pattern on the leaves which slows photosynthesis and therefore growth
• Salmonella


  A bacteria that causes food poisoning and infects the intestinal tract
• Gonorrhoea


  A sexually-transmitted bacterial disease which causes thick green or yellow discharge and pain when urinating
• Rose black spot


  A fungal disease where black spots develop on rose plant leaves, which often turn yellow and drop early
• Malaria


  A disease with fever symptoms, caused by protist parasites in the blood that are transmitted by mosquitoes
• Vector


  An organism that transmits a disease or parasite from one animal or plant to another
• Droplet infection


  An infection that is transmitted by sneezing and coughing pathogens carried by droplets in the air
• Airborne transmission


  Some infectious agents can be transmitted through the air over time and distance
• Sexually transmitted infection (STIs)

  Also called sexually transmitted diseases or STDs, the term used to describe infections that are spread through sexual activity such as intercourse
• Ingestion


  Infection can occur when eating uncooked products such as meat, drinking dirty water or touching the mouth after touching a dirty surface, some pathogens can survive in the extreme pHs of the digestive system
• Areas of the body that pathogens can enter

  Nose and mouth, respiratory system, digestive system, reproductive or urinary systems, eyes and tear ducts, any orifice, via injection to the blood, through wounds or damage to the skin
• Non-specific defence


  A general defence that works the same against all pathogens
• Immune system


  The cells and tissues that recognize and attack foreign substances in the body
• White blood cell


  A blood cell that fights disease
• Phagocytosis


  When a white blood cell called a phagocyte engulfs a pathogen to destroy it with enzymes
• Antibody


  A protein that binds to a specific antigen and triggers the pathogens to be destroyed
• Antibody production


  When a white blood cell called a lymphocyte produces antibodies
• Antitoxin


  A substance that neutralises the poisonous products of microorganisms
• Antimicrobial secretions


  Secretions from the skin and nose that reduce bacterial growth
• Barrier


  A physical body defence such as skin that prevents pathogens entering the body
• Mucus


  A thick and sticky substance produced by goblet cells in the body, traps invasive pathogens and particles
• Cilia


  The hair-like projections on the outside of trachea cells that move mucus and other substances away from the lungs
• Stomach acid


  Hydrochloric acid in the stomach that kills pathogens
• Enzymes


  Certain enzymes in the body such as lysozymes found in tears are capable of destroying pathogens
• Antigen


  A substance on a foreign cell or pathogen that triggers an immune response
• Phagocyte


  The white blood cell responsible for phagocytosis via ingestion
• Lymphocyte


  The white blood cell responsible for antibody and antitoxin production
• Platelets


  Structures in the blood responsible for blood clotting, prevents further bleeding and reduces the chances of pathogens entering the blood, can also bind to pathogens
• Vaccination

  Introduction of an antigen or a weakened or inactive form of a pathogen to generate immunity
• Lymphocyte

  The white blood cell responsible for antibody production