Infection and response

• Pathogens include: Viruses, Bacteria, Fungi, and Protists
• A pathogen is a microorganism that causes communicable diseases that can affect plants or animals
• They spread via

  • air
  • water
  • direct contact
  • contaminated food
• Viruses

  • are very small
  • cannot reproduce themselves
  • viruses enter a cell then use its biochemistry to make many copies of itself
  • this then causes the cell to burst which in turn releases the copies into neighbouring cells and the cycle repeats
  • the damage and destruction of the cells is what makes an individual feel ill
• Bacteria


  • multiply rapidly via binary fission
  • produce toxins that damage cells causing us to feel ill
  • single-celled organisms
  • Bacteria can reproduce rapidly in the appropriate conditions: warm, moist areas with a good supply of oxygen.
• Protists


  • Some are parasitic meaning they use humans and animals as their host
  • transported by vectors and spread the disease to new hosts like insects however the vectors don't get the disease e.g. malaria the
  • eukaryotic
  • make us feel ill by damaging our tissues
• Fungi


  • eukaryotic
  • can be unicellular or multicellular
  • multicellular fungi have hyphae (thread like structures) that produce spores that can be spread to other organisms or produce more fungi
  • Hyphae are able to grow and penetrate tissues such as human skin or the surface of plants
• How to stop the spread of communicable disease


  • Improve hygiene: hand washing, sanitation
  • Isolation and quarantine
  • Removing vectors: using pesticides or removing their habitat
  • Vaccination
• What is the process of vaccination?


  1. Inject a dead or inactive pathogen into the blood
  2. white blood cells recognise the foreign antigens on the pathogen and produce specific antibodies against them
  3. Memory cells are also produced so upon a secondary infection antibodies are produced much quicker and more are produced
• Viral diseases


  • Measles
  • HIV
  • Tobacco mosaic virus (plants)
• Measles

  • symptoms: red rash, fever
  • spread by droplets e.g. coughing and sneezing
  • being prevented by vaccination for young children
• HIV

  • Symptoms: Flu-like at first then the virus attacks the immune system and leads to AIDS so the body is susceptible to many different diseases as the immune system is weak
  • Spread by sexual contact or exchanging bodily fluids
  • Being prevented by the using condoms, not sharing needles and the development of antiretroviral drugs to stop the development of AIDS from HIV by stopping the virus replicating in the body
• Tobacco mosaic virus


  • Symptoms: discolouration of the leaf, the affected part of the leaf cannot photosynthesize so the plant can't grow or produce sugars
  • Spread by contact between diseased plants and healthy plants, insects act as vectors
  • Prevented by pest control and growing TMV resistant strains of plants
• Bacterial diseases


  • Salmonella
  • Gonorrhoea
• Salmonella


  • Symptoms: Fever, stomach cramps, vomiting, diarrhoea
  • Spread by the bacteria that live in the gut of different animals which we ingest when we eat the meat. These bacteria can be found in raw meat and eggs, unhygienic conditions
  • Being prevented by vaccination of poultry, separation of raw and cooked food, cook food thoroughly
• Gonorrhoea


  • Symptoms: Thick yellow or green discharge from the genitals, pain when urinating
  • Spread via unprotected sexual contact
  • Prevented by using contraception like condoms or abstaining and antibiotics like penicillin
• Fungal diseases


  • Rose black spot
• Rose black spot


  • Symptoms: purple or black spots on the leaves of rose plants, reduces the area of the leaf available for photosynthesis, leaves turn yellow and drop early
  • Spread by the spores of the fungus being transported in water (rain) or wind
  • Prevented by chopping off all infected leaves and burning them or spraying them with fungicides
• Protist disease


  • Malaria
• Malaria

  • Symptoms: Fevers and shaking
  • Spread by mosquitos (the vector). If a mosquito is carrying malaria, then it transfers the infection into a person's bloodstream when it bites them
  • Prevented by using insecticide coated nets, destroying mosquito breeding sites, antimalarial drugs
• Non-specific defence system


  designed to prevent any pathogens from entering the body and causing harm

  • skin
  • stomach acid
  • tears
  • trachea and bronchi
  • the nose
• How does the skin work as a defence system?

  • physical barrier
  • produces antimicrobial secretions to kill pathogens
  • has good bacteria that compete with pathogens for space and nutrients preventing them from growing on our skin
• How does stomach acid work as a defence system?


  • Glands in the stomach produce hydrochloric acid that kills any pathogens that enter your stomach via mucus or food and drink
• How do tears work as a defence system?


  • tears contain enzymes that destroy any pathogens that make contact with our eyes
• How does the nose work as a defence system?


  • Has hairs and mucus which traps and prevents particles from entering your lungs
• How do the trachea and bronchi work as defence systems?


  • secrete mucus to trap pathogens
  • cilia (hair-like structures on cells) beat to waft mucus upwards so it can be swallowed and go to the stomach where its killed
• 3 types of functions white blood cells can do

  • phagocytosis (engulfing and consuming pathogens)
  • producing antibodies
  • producing antitoxins
• Lymphocytes produce antitoxins which are molecules that neutralise the toxins released by the pathogen
• Lymphocytes produce specific antibodies that bind to a specific antigen causing the pathogens to clump together. This makes it easier for phagocytes to find and engulf them
• Memory cells


  If you become infected again with the same pathogen, the specific antibodies will be produced faster and more will be produced so the individual becomes immune.
• Antibiotics are medicines that kill bacterial pathogens inside the body, without damaging body cells e.g. penicllin
• Antibiotics are specific
• Antibiotics do not affect viruses as viruses stay inside host cells so they wouldn't be able to kill them without killing the cells
• Process of phagocytosis 


  1. The phagocyte tracks down a pathogen and binds to it
  2. The phagocyte's membrane will then surround the pathogen and engulf it
  3. The enzymes inside the phagocyte break down the pathogen in order to destroy it
• Painkillers such as aspirin only treat the symptoms of the disease rather than the cause
• How does bacteria become antibiotic resistant


  1. A population of bacteria infect somebody, and that person takes antibiotics to kill the bacteria
  2. Some bacteria get a random mutation that makes them less susceptible to the antibiotic (or completely resistant)
  3. These antibiotics kill all the bacteria except those that are resistant
  4. The resistant strains of bacteria survive and now have more resources to grow and multiply
  5. More mutations may arise leading to greater resistance. There is now a strain of bacteria that can't be killed be antibiotics
• To help prevent strains of resistant bacteria from developing:


  • Doctors should only prescribe antibiotics if they are needed and not for minor or viral infections
  • Patients should complete their course of antibiotics to ensure all bacteria are killed
• The process of antibiotic resistance can keep happening until the bacteria is resistant to many antibiotics as when a antibiotic doesn't work the patient will get another one etc
• A superbug is a bacteria strain that is resistant to many types of antibiotics e.g. MRSA which often affects people in hospital
• In the past most drugs were found from plants and microorganisms like aspirin from willow trees, or penicillin from penicillium mould. However nowadays most drugs are synthesised by chemists in a lab