infection & response

• Pathogens


  Microorganisms that cause communicable diseases
• Types of pathogens


  • Bacteria
  • Viruses
  • Protists
  • Fungi
• Bacteria


  • Small prokaryotic cells that can infect both plants and animals
  • Reproduce rapidly in optimum conditions
  • Release toxins that damage cells and tissues
  • Can be useful, e.g. digest cellulose
• Viruses


  • Not cells, not classified as living organisms
  • Rely on host cells to survive and reproduce
  • Insert genetic material into host cells and use their machinery to reproduce
  • Can cause host cells to burst and release more viruses
• Protists


  • Eukaryotic organisms, often single-celled
  • Can be parasitic and live on or in a host organism
  • Often transferred between hosts by vectors
• Fungi


  • Grow on living tissues, can be single-celled or have a body made of hyphae
  • Hyphae penetrate living tissues, causing infections
  • Produce spores to spread infections
  • Most common in plants, but some can infect animals
• Ways communicable diseases are spread between organisms

  • Air
  • Water
  • Direct contact
  • Vectors
• Preventing the spread of diseases

  1. Keeping good hygiene

  2. Isolating diseased individuals

  3. Killing vectors or destroying their habitats

  4. Vaccinations
• Disease Examples


  • Measles
  • HIV
  • Tobacco Mosaic Virus (TMV)
  • Salmonella
  • Gonorrhoea
  • Rose Black Spot Disease
• Measles


  Highly contagious viral disease in humans spread between people by cough and sneeze droplets (airborne), symptoms include red skin rash and fever, serious complications can be fatal, no proper treatment but there is a vaccine, mainly seen in children so are often vaccinated against it at an early age
• HIV


  Viral disease that can lead to AIDS, spread through sexual contact, exchanging bodily fluids, and from mother to baby during birth and breast milk, first appears as flu-like symptoms then travels to the lymph nodes to destroy cells involved in the immune response, can stay hidden until the immune system is so damaged that it cannot cope with other infections and cancers (AIDS), can be treated with antiretroviral drugs which slow the virus down by preventing it from attacking immune cells
• Tobacco Mosaic Virus (TMV)


  A plant virus affecting many different species, including tomatoes, a distinct mosaic pattern visible on leaves, discolouration of leaf limits photosynthesis and stunts growth
• Salmonella


  Bacteria that causes food poisoning by releasing toxins, symptoms include fever, abdominal cramps, vomiting and diarrhoea, may have been acquired by the animal before it was killed for food or when the food was being prepared (if conditions were unhygienic), poultry are vaccinated against salmonella (in the UK) to prevent the spread of the disease
• Gonorrhoea


  Bacterial infection spread by sexual contact (it is a sexually transmitted disease, STD), symptoms include thick yellow or green discharge from the vagina or penis and pain while urinating, used to be treated with the antibiotic penicillin until strains of the bacteria became resistant, now the spread of the disease is prevented using antibiotics and by encouraging people to use barrier methods such as condoms during sexual activities
• Rose Black Spot Disease

  Fungal disease affecting rose plants, black or purple dots visible on leaves causing them to turn yellow and eventually drop off, plant will struggle to grow because less photosynthesis can happen, spread in water and wind, fungicides can be used to treat the plant or infected leaves can be removed and destroyed to stop the spread