infection and response

• There Are Several Types of Pathogen
• Pathogens


  Things that can enter the body and cause disease
• Types of pathogens


  • Bacteria
  • Viruses
  • Protists
  • Fungi
• Bacteria


  • Very small living cells (about 100 the size of your body cells)
  • Can produce toxins that damage your cells
  • Can multiply rapidly inside your body
• Viruses


  • Not cells, much smaller than bacteria (about 1/100th the size of a bacterium)
  • Can replicate rapidly inside your body
  • Can damage cells and cause them to burst releasing new viruses
• Protists


  • Single-celled eukaryotes
  • Some are parasites that live inside other organisms and can cause them harm
  • Often transferred to the organism by a vector
• Fungi


  • Some are single-celled, others have a body made up of hyphae (thread-like structures)
  • Hyphae can grow and penetrate human skin and plant surfaces, causing diseases
  • Hyphae can produce spores which can be spread to other plants and animals
• Ways pathogens can be spread

  • Water
  • Air
  • Direct contact
• Some pathogens can be picked up by drinking or bathing in dirty water, e.g. cholera
• Some pathogens can be carried in the air and breathed in, e.g. influenza virus
• Some pathogens can be picked up by touching contaminated surfaces, e.g. athlete's foot fungus
• How viruses cause cell damage

  1. Virus enters cell

  2. Virus uses cell machinery to replicate itself

  3. Cell bursts releasing new viruses
• Viral diseases you need to know about

  • Measles
  • HIV/AIDS
  • Tobacco mosaic virus
• Measles


  Highly contagious viral disease that can be serious or even fatal
• HIV


  Virus that attacks the immune system, can lead to AIDS if untreated
• Tobacco mosaic virus


  Virus that affects many plant species, causes mosaic pattern on leaves
• Fungal disease you need to know about

  • Rose black spot
• Rose black spot


  Fungus that causes black spots on rose leaves, can make leaves turn yellow and drop off
• Protist disease you need to know about

  • Malaria
• Malaria


  Disease caused by a protist, part of its life cycle takes place in mosquitoes which act as vectors
• Symptoms of measles include a skin rash
• Rose black spot can be treated by removing and destroying affected leaves, and using fungicides
• Bacterial diseases you need to know about

  • Salmonella food poisoning
  • Gonorrhoea
• Salmonella food poisoning


  Caused by bacteria that produce toxins, can cause fever, stomach cramps, vomiting and diarrhoea
• Gonorrhoea


  Sexually transmitted bacterial disease, causes pain when urinating and discharge
• Salmonella in the UK is controlled by vaccinating chickens and turkeys
• Gonorrhoea is becoming harder to treat as the bacteria have become resistant to some antibiotics
• Simple hygiene measures can help prevent the spread of disease
• Destroying vectors like insects can prevent the spread of disease
• Isolating infected individuals can prevent them from passing on a communicable disease
• Vaccination can prevent people from developing and spreading communicable diseases
• Phagocytosis


  White blood cells consuming and digesting foreign cells
• Respiratory system defences


  • Skin acts as a barrier
  • Mucus traps pathogens
  • Cilia move mucus and trapped pathogens out
  • Stomach acid kills pathogens
• Immune system


  • White blood cells patrol for pathogens
  • White blood cells can consume pathogens (phagocytosis)
  • White blood cells can produce antibodies to target specific pathogens
  • White blood cells can produce antitoxins to counteract toxins
• People with a weakened immune system, e.g. from HIV, are more susceptible to infections
• Vaccination


  Injecting small amounts of dead or weakened pathogens to stimulate the body to produce antibodies against them
• Vaccines have helped control many communicable diseases in the UK
• High vaccination rates can prevent disease outbreaks by creating 'herd immunity'
• Vaccines don't always work and can sometimes have side effects, but serious reactions are very rare
• Antibiotics can kill or prevent the growth of bacteria, but don't work against viruses