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• The Human Immune System


  Part of your body that helps set the mood and has a chance to attack pathogens
• How the Human Immune System Can Attack Pathogens

  1. Phagocytes destroy pathogens

  2. White blood cells recognise antigens on pathogens

  3. Immune system is triggered to destroy pathogens and cells with foreign antigens
• Ways the Immune System Attacks

  • Consuming them (phagocytosis)
  • Producing antibodies
  • Producing antitoxins
• Phagocytes


  • White blood cells that can engulf and destroy foreign cells
• Antibodies


  Proteins produced by white blood cells that lock onto antigens on invading cells
• Antibody Production


  1. White blood cells detect pathogen

  2. White blood cells divide to produce more of the same type (clones)

  3. Antibodies are produced rapidly and carried around the body

  4. Antibodies disable or tag pathogens to help phagocytes destroy them

  5. Memory cells remain after pathogen is fought off to trigger rapid antibody production if infected again
• Antitoxins


  Produced by white blood cells to counteract toxins produced by pathogens
• Communicable Diseases


  Diseases caused by Pathogens
• Types of Pathogens


  • Bacteria
  • Viruses
  • Protists
  • Fungi
• Bacteria


  • Microscopic cells (about 1/100th the size of your body cells)
  • Can produce toxins that damage your cells and tissues
• Viruses


  • Not cells, very tiny (about 1/100th the size of a bacterium)
  • Replicate themselves inside the infected organism's cells, causing the cells to burst and release more viruses
• Protists


  • Eukaryotic, usually single-celled, vary in size
• Fungi


  • Some are single-celled, others have a body made up of thread-like structures called hyphae
  • Hyphae can grow and penetrate human skin and the surface of plants
  • Can produce spores that can spread to other plants and animals
• Ways Pathogens Can Spread

  • Water
  • Air
  • Surfaces
  • Body
  • Animal vectors
  • Food
• Pathogens spread through water

  • Cholera (bacterial infection) spreads when drinking water is contaminated with the bacteria from other sufferers
• Pathogens spread through air


  • Influenza virus spreads through droplets produced when coughing or sneezing
• Pathogens spread through surfaces

  • Tobacco mosaic virus (TMV) spreads when touching infected plant leaves
• Pathogens spread through body contact

  • Athlete's foot (fungal infection) commonly spreads by touching the same things as an infected person
• Pathogens spread through animal vectors


  • Malaria is spread by mosquitoes
• Pathogens spread through food


  • Some bacteria are found in certain foods
• Communicable diseases are diseases that can be transmitted from one organism to another
• Pathogens are microorganisms that cause communicable diseases
• When the human body's defences are not working properly, it struggles to cope with infections
• Reducing and Preventing the Spread of Disease

  The best way of dealing with disease is sometimes to just avoid contact with pathogens in the first place
• In some cases, such as with large hands of animals


  It might be necessary to the infected Individuals to prevent genumbers of other animals from getting the d
• The disse may still spread if it is present in other individuals withes
• Isolating infected individuals-this amants them from p Individuals should also be prevented from traveling, and spreading it even further
• Although this belts society, it can be difficult for an infected person as they can't be with their loved ones
• Sometimes it can be difficult to n the needs of an inchidul while doing what is best for sist
• Vaccination


  Vaccinating people and animals against communicable diseases means ther they develop the infection and then passion to others
• Contraception


  Using condoms prevents sexually transmitted infections (HIV-see p.10) from being transmitted between people during s
• Reducing the Spread of Disease in Plants

  1. Bagulding movement of plant material-this makes sure that infected plants don't come into contact with healthy plants, eg. plant nurseries are not allowed to sell plants which have grown gall doesse

  2. Destroying infected plants-this stops them being sources of infection, but can be costly to a farmer

  3. Only using sources of healthy seeds and plants-this stops the disease from being introduced into a population

  4. Op rotation-many pathogens are specific to a particular plant. Changing the type of planta that are grown stops the pathogens becoming established in an area. However, it may mit how fitable a farm is if it has to change farming practices for a different crop each year

  5. Polyculture (growing different types plants in a single area at the same time)-if a pathogen g to a single plant enters one plant, it's less likely to infect neighbouring plants because they are different species-limiting the spread of the pathogen through the crop

  6. Chemical control-for example, fungicides can be used to kill fungal pathogens. This can be an effective method but may also lead to the evolution of resistant strains of the pathogen (see page 70)

  7. Bogical control-this is when another organism is used to control a pest or pathogen. For example, ladybirds eat aphids (an insect pest) so ladybirds can be released into an area to reduce aphid numbers. However, in some cases, the control organism may become a pest itself and cause more problems
• Plant diseases can reduce food sources for many organisms and can damage habitats for other organisms in an ecosystem
• The s spread of disease
• Reducing and Preventing the Spread of Disease


  The best way of dealing with disease is sometimes to just live with it, the spread can be reduced or prevented
• The Spread of Disease Can Be Reduced or Prevented in Animals
• If disease spreads rapidly

  It can result in huge losses of health and food
• Measures to prevent disease spread

  • Basic hygiene measures (e.g. washing hands regularly)
  • Treating wounds to stop pathogens entering the blood
  • Living in sanitary conditions
  • Destroying infected animals to prevent them passing disease to others
• Vaccinating people and animals against communicable diseases means they won't develop the infection and then pass it to others
• Using contraception (e.g. condoms) prevents sexually transmitted infections (e.g. HIV) from being transmitted between people