Infection and Response

• pathogens are microorganisms that enter the body and cause disease


  they cause communicable diseases that can easily spread

  both plants and animals can be infected by pathogens

  pathogens can be BACTERIA, VIRUSES, PROTISTS, or FUNGI
• Bacteria are very small cells which can reproduce rapidly inside your body


  they can make you feel ill by producing TOXINS that damage your cells and tissues
• Viruses are not cells- they are smaller


  they can reproduce rapidly inside your body

  they live inside your cells and replicate themselves using the cell' machinery to produce many copies of themselves

  the cell will then burst, releasing the new viruses

  the cell damage makes you feel ill
• protists are single-celled eukaryotes


  some protists are parasites- parasites live on or inside other organisms and can cause them damage. they are often transferred to the organism by a vector, which doesn't get the disease itself
• fungi come in different shapes


  some are single celled

  others have a body which is made up of HYPHAE- thread like structures

  these hyphae can grow and penetrate human skin and the surface of plants causing disease

  the hyphae can produce spores, which can be spread to other plants and animals
• pathogens can be spread in different ways


  water

  air

  direct contact
• pathogens can be spread through water


  some pathogens can be picked up by drinking or bathing in dirty water

  cholera is a bacterial infection that's spread by drinking water contaminated with the diarrhoea of other sufferes
• pathogens can be spread through air


  pathogens can be carried in the air and can then be breathed in

  some airborne pathogen are carried in the air in droplets produced when you cough or sneeze- the influenza virus is spread this way
• pathogens can be spread through direct contact


  some pathogens can be picked up by touching contaminated surfaces including the skin

  athletes foot is a fungus which makes skin itch and flake off, it is commonly spread by touching the same things as an infected person
• Measles is a VIRUS


  measles is spread by droplets from a contaminated sneeze/cough

  people with measles develop a red skin rash, and a fever

  measles can be serious or even fatal if there are complications (pneumonia)

  most people are vaccinated when they are young
• HIV is a VIRUS

  HIV is a virus spread by sexual contact, or exchanging bodily fluids such as blood from shared needles

  initially causes flu-like symptoms, usually the person doesn't experience symptoms for a few years, HIV can be controlled using antiretroviral drugs which stop the virus replicating

  the virus attacks the immune cells meaning it can't cope with other infections or cancer- late stage HIV or AIDS
• Tobacco Mosaic Virus (TMV)


  TMV is a virus that affects many species of plants

  it cause a mosaic pattern on the leaves of plants, causing them to become discoloured

  the discolouration means photosynthesis can't be carried out well, so the plant growth is stunted
• Rose Black Spot is a FUNGAL disease


  rose black spot is a fungal disease that cause purple/black spots on the leaves of rose plants- can turn yellow and drop off

  photosynthesis happens less- plant doesn't grow well

  spreads through the environment- water/wind

  gardeners treat the disease using fungicides and by stripping the plant of affected leaves- the leaves need to be destroyed so they cannot spread
• malaria is caused by a PROTIST


  part of the malaria's life cycle takes place inside a mosquito

  the mosquitoes are vectors that pick up the malaria protist when feeding on the infected animal

  every time the mosquito feeds on another animal, it infects it by invading the protist into the blood vessels

  malaria cause repeating episodes of fever- can be fatal

  people can be protected using mosquito nets or insecticides
• salmonella is a BACTERIAL disease


  salmonella is a bacteria that causes food poisoning

  infected people can suffer fever, stomach cramps, vomiting, diarrhoea

  these symptoms are cause by the toxins that bacteria produces

  salmonella is passed through food that has been contaminated
• gonorrhoea is a BACTERIAL disease

  gonorrhoea is a sexually transmitted disease (STD)

  STD's are passes through sexual contact

  a person with gonorrhoea will get pain when they urinate, thick yellow green discharge from the vagina or penis

  originally treated with penicillin, but strains have become resistant

  people can be treated with antibiotics and should have barrier methods of contraception
• The spread of disease can be reduced or prevented

  being hygienic

  destroying vectors

  isolating infected individuals

  vaccination
• being hygienic can reduce the spread of disease


  using simple hygiene measures can prevent the spread of disease

  washing hands etc
• destroying vectors can prevent the spread of disease

  by getting rid of organisms that spread disease, you can prevent the disease from being passed on

  vectors that are insects can be killed using insecticides or by destroying their habitat so they can no longer breed

  the spread of malaria can be prevented by stopping mosquitoes breeding
• isolating individuals can reduce the spread of disease

  if you isolate someone who has a communicable disease, it prevents them from passing it on to somebody else
• vaccination can prevent the spread of disease

  vaccinating people and animals against communicable diseases means that they can't develop the infection and then pass it on to someone else

  most poultry in the united kingdom is vaccinated against salmonella
• the human body has features to prevent the entry of pathogens


  the skin acts as a barrier and secretes antimicrobial substances which kill pathogens

  hairs and mucus in the nose trap particles that may contain pathogens

  the trachea + bronchi secrete mucus to trap pathogens, they are lined with cilia which waft the mucus to the back of the throat

  the stomach produces hydrochloric acid to kill pathogens
• the immune system can attack pathogens


  white blood cells are in charge of destroying invading pathogens

  -consuming them

  -producing antibodies

  -producing antitoxins
• phagocytosis


  white blood cells can engulf foreign cells and digest them
• white blood cells can produce antibodies


  every invading pathogen has an antigen on their surface

  when some types of white blood cell come across a foreign antigen they produce proteins called antibodies to lock onto the invading cells so they can be found and destroyed by other white blood cells

  antibodies are produced rapidly and carried round the body to find all similar bacteria or viruses
• white blood cells can become memory cells


  if the person is infected with the same pathogen again the white blood cells will rapidly produce the antibodies to kill it, the person is naturally immune to that pathogen and won't get ill
• white blood cells can produce antitoxins


  these toxins counteract toxins produced by the invading bacteria
• vaccinations can prevent future infections


  vaccination involves injecting a dead or weakened version of a pathogen into the body. these carry antigens which cause your body to produce antibodies to attack them

  if the body is infected with that pathogen again, the white blood cells rapidly mass-produce antibodies to kill the pathogen
• pros of vaccination


  vaccines help control a lot of communicable diseases

  big outbreaks can be prevented if the majority of the population is vaccinated (herd immunity)
• cons of vaccination


  sometimes the vaccine doesn't work

  the vaccine can cause side effects and bad reactions can occur
• some drugs just relieve symptoms


  painkillers are drugs that relieve pain-they reduce the symptoms

  antibiotics kill the bacteria causing the problem without killing your body cells different antibiotics kill different bacteria so it is important to use the correct one- strains have become resistant

  antibiotics don't destroy viruses- viruses reproduce using the body cells which makes it difficult to produce a drug that kills just the virus
• bacteria can become resistant to antibiotics


  bacteria can mutate- the mutations can cause them to be resistant

  when the infection is treated, the non-resistant bacteria will be killed

  the individual resistant bacteria will survive and reproduce, meaning the population of the resistant strain will increase

  the resistant strain can cause a serious infection that cannot be treated

  to slow down the rate of resistant bacteria, doctors should avoid over prescribing antibiotics people must finish the course of antibiotics
• many drugs originate from plants


  plants produce a variety of chemicals to defend themselves against pests and pathogens

  some of theses chemicals can be used to treat human diseases or relieve symptoms

  a lot of current medication were discovered by studying plants used in traditional cures
• some drugs were extracted from microorganisms


  Alexander Fleming cleared out some Petri dishes containing bacteria- some had mould on it and the area around the mould was free of bacteria

  he discovered the mould was a substance that killed the bacteria
• today, drugs are made on a large scale in the pharmaceutical industry


  they are synthesised by chemists in labs
• There are three main stages in drug testing


  preclinical testing

  -human cells

  -live animal cells

  clinical trial
• preclinical testing


  tested on human cells and tissues, but cannot see how they affect whole systems

  live animals to test efficacy(whether the drug works) and to find out its toxicity(how harmful it is) and to find the best dosage(the concentration and how often)
• clinical trial


  first tested on healthy volunteers to make sure it doesn't have any harmful side effects- at the start a very low dose is given, which is gradually increased

  if the results are good, the drug can be tested on people suffering from the illness

  the optimum dosage is found, the most effective with the least side effects
• drugs are tested on people suffering with the disease


  they are split into two groups

  some are given placebos(a substance that is like the drug being tested but has no effect) while others are given the new drug
• Monoclonal Antibodies are identical antibodies


  antibodies are produced by b-lymphocytes (A type of white blood cell)

  monoclonal antibodies are produced from lots of clones of a single white blood cell

  this means all the antibodies are identical and will target one specific antigen