Topic 3 - Infection and response

• Viruses

  • Very small
  • Move into cells and use the biochemistry to make copies of themselves.
  • Leads to the cell bursting and releasing all copies into bloodstream.
  • The damage and destruction of the cells make the organism feel ill
  • Scientists haven't developed medicines to kill them
• Bacteria

  • Small
  • Multiply very quickly through binary fission
  • Produce toxins which can damage cells
  • Not all bacteria's are harmful
• Fungi

  They can either be single celled or have a body made of hyphae

  They can produce spores which can spread to other organisms
• Pathogens

  • Viruses
  • Bacteria
  • Protists
  • fungi
• how pathogens are spread

  • Direct contact
  • By water
  • By air (e.g. droplet infection which is when sneezing coughing or talking expels pathogens in droplets which can be breathed in.)
• How to limit the spread of pathogens

  • Improve hygiene
  • Reduce contact with infected individuals (isolation)
  • Remove vectors
  • Vaccination
• Measles

  Symptoms:

  Fever and skin rash which can lead to pneumonia (lung infection), encephalitis (Brain infection) and blindness.

  Spread by droplet infection but vaccinations for young children are used to avoid transmission.
• HIV

  Symptoms:

  Initially flu like symptoms then the virus attacks the immune system which leads to AIDS (The body is very vulnerable)

  Its spread by sexual contact or exchange of bodily fluids. However, it can be prevented by using a condom and not sharing needles. Also you can use antiretroviral drugs to prevent the virus replicating.
• Tobacco mosaic virus (TMV)

  Symptoms:

  Discolouration of the leaves - the affected part can't photosynthesise which means the plant won't grow as much.

  Its spread by contact between diseased plants and insects as vectors but can be prevented by pest control and growing TMV resistant strains
• Viruses structure

  • They have no nucleus organelles or cytoplasm
• Viruses

  • Measles
  • HIV
  • Tobacco mosaic virus (TMV)
• Bacterial diseases

  They are increasing since they are becoming resistant to antibiotics
• Salmonella

  Symptoms:

  You can get a fever, cramps, vomiting and diarrhoea all of which are trying to remove the infection from the gut. Doesn't last more than a few days and is more severe in children and elderly due to dehydration.

  Its spread by contaminated food that hasn't been cooked properly. Its prevented by chicken being vaccinated again salmonella as well as proper hygiene in the kitchen.
• Gonorrhoea

  Symptoms:

  thick yellow or green discharge from genitals as well as pain when urinating. If left untreated can cause infertility and pelvic pain, also babies born to women with it can get eye infections and be born blind. However some people are asymptomatic.

  Its spread through unprotected sex and a condom can prevent it.
• asymptomatic

  don't show any symptoms
• Bacteria examples

  • Salmonella
  • Gonorrhoea.
• Rose black spot

  Symptoms:

  purple or black spots on leaves which then turn yellow and drop off. This loss of leaves means there's less chloroplasts for photosynthesis and therefore less energy to make flowers.

  Its spread from spores from fungus which are carried in the wind or water. It can be prevented with fungicide chemicals, leaves removed and burnt to prevent infection or you can breed varieties which are resistant.
• Fungi examples

  • Athletes foot
  • Rose black spot
• Protists

  • Some are parasitic - they use animals and humans as their hosts
  • eukaryotic cells which are usually unicellular organisms
  • Often need a vector to transfer from one host to the next.
• Malaria

  Symptoms:

  Fever and shaking which can weaken the host so much it could be fatal.

  Spread by mosquito vector but if diagnosed early can be treated with a combination of drugs - however most strains have become resistant. We can also try to control mosquito populations.
• Controlling mosquito population to reduce spread of malaria.

  • Using insecticides
  • Prevent the mosquitoes from breeding by spraying to kill the eggs or removing water sources.
• Malaria life cycle

  • a female mosquito bites the human
  • The malaria parasite infects the liver and reproduces asexually.
  • The malaria parasite is now in the blood of humans
  • Mosquito consumes infected blood when feeding
  • Sexual reproduction of malaria parasite
  • Repeat
• protist example

  Malaria
• Non specific immune system

  • Skin
  • Nose
  • Trachea and bronchi
  • Stomach
• Skin as a defence system

  • Acts as a physical barrier
  • Good microorganism compete with bad microorganisms for space and nutrients
  • Secretes antimicrobials to kill pathogens
• The nose as a defence

  • Has hairs and mucus which prevent particles from entering the lungs
• Trachea and bronchi as a defence

  • Secrete mucus to trap pathogens
  • Cillia (Hair like structures) waft mucus upwards so it can be swallowed
• The stomach as a defence

  Produces hydrochloric acid that kills any pathogen in your mucus, food or drink
• Specific immune system

  Acts to destroy pathogens which pass through the non specific immune system. Mostly consisting of white blood cells
• How white blood cells act

  • Phagocytosis
  • Producing antibodies
  • Producing antitoxins
• Phagocytosis


  When phagocytes engulf pathogens and then release enzymes to digest and break down it to destroy it
• Producing antibodies

  • Lymphocytes produce antibodies
  • Antibodies are specific to the antigens on the surface of a pathogen
  • These antibodies with a complementary shape to the antigen bind to the pathogens which will start to clump together resulting on it being easier for white blood cells to find them
  • If the same pathogen attacks again the lymphocytes will remember which antibody to produce.
• Producing antitoxins

  Lymphocytes can produce antitoxins which neutralise the effect of the toxin
• Vaccination

  • Involves exposing an individual to the small quantities of the dead or inactive antigens of a pathogen
  • This triggers an immune response which results in the lymphocytes producing memory cells which can make antibodies against it
  • If the individual gets infected by this pathogen again it will have the memory to produce the antibodies again.
• Advantages of vaccination

  • Diseases that were once common are now fairly rare
  • Epidemics can be prevented if large numbers of the population are vaccinated
• Disadvantages of vaccination

  • The vaccine doesn't always give immunity
  • there can be side effects to the vaccine e.g. fevers or a rash
• Herd immunity

  If a large number of the population are vaccinated, it is unlikely that an unvaccinated individual will become infected with the pathogen
• Antibiotics

  Medicines that treat the cause of the disease
• Painkillers

  Medicines which treat the symptoms of a disease
• Antibiotics

  • Help to cure bacterial disease by killing bacteria inside the body
  • The use of antibiotics reduces death
  • Only certain antibiotics will work on certain diseases
  • They work by stopping bacteria cellular processes
  • Will not work against viruses since they reproduce inside cells so it would be difficult to kill them without damaging the body