Infection and Response

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Types of Pathogen

A pathogen is a microbe that causes a disease

There are 4 types of pathogen :

  • Virus
  • Protist
  • Fungus
  • Bacteria

They are transmitted via :

  • Unprotected sex
  • Touching an infected person
  • Insect bites
  • Air droplets 
  • Contaminated food / drink
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Virus Diseases

Tobacco Mosaic Virus

  • Transmitted through infected tools
  • Causes a mosaic of brown spots on leaves, and stunts plant growth
  • Treated by removing infected leaves, washing tools and rotating crops

Measles

  • Transmitted through water droplets from sneezing
  • Causes red eyes, a fever and small white spots on the inside of cheeks
  • Treated by paracetemol and cotton wool to clean red eyes

HIV

  • Transmitted through unprotected sex
  • Causes initially flu-like symptoms but if untreated can damage the immune system
  • Treated through antiretroviral drugs
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Bacteria Diseases

Gonorrhea

  • Transmitted through unprotected sex
  • Causes green / yellow discharge from penis / vagina and pain while urinating
  • Treated by antibiotics (but many strains are resistant so it's best to just use protection)

Salmonella

  • Transmitted through contaminated food (namely raw chicken)
  • Causes diarrhoea, vomiting and stomach cramps
  • Prevented by washing hands before eating and cooking raw food fully
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Fungal and Protist Diseases

Fungal - Rose Black Spot

  • Transmitted through water and wind
  • Causes purple / black spots on leaves and limited plant growth
  • Treated by fungicides and destroying infected leaves

Protist - Malaria

  • Transmitted through mosquito bites
  • Causes recurrent fever, sweats and chills and sometimes is fatal
  • Prevented by using insect repellant and using nets to avoid being bitten
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Body Defences

Defences to Stop Pathogens Getting in

  • The skin is a natural barrier
  • Tears help kill pathogens
  • Stomach acid kills pathogens
  • Mucus traps pathogens and cilliated cells sweep them out

The Immune System

  • Phagocytes engulf and destroy pathogens
  • Lymphocytes produce antitoxins to counter the toxins released by bacteria
  • They also produce antibodies to stick onto the pathogen's antigens
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Vaccinations

Vaccinations stimulate the immune system to produce antibodies for a specific pathogen

The Stages of a Vaccine :

  • A mild / weaker form of a pathogen is injected
  • It is mild so you don't get too ill from it
  • This stimulates the immune system to make antibodies for it, but it is quite slow
  • The antibody is found and the vaccine pathogens are destroyed
  • The antibody is remembered by immunomemory cells
  • Upon reinfection of the same type of pathogen, the response is quicker
  • This is because the W.B.C's remember what antibody to make and make lots quickly

The first vaccine was found by Edward Jenner for smallpox

One example of a modern vaccine is MMR (measles, mumps, rubella)

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Drugs

Drugs can either kill the pathogen causing disease or supress the symptoms of it#

Antibiotics only kill bacteria. The first one (penicillin) was discovered by Fleming in 1928.

Stages in Drug Testing

  • The drug is first tested on cells to make sure it doesn't kill them
  • Then it is tested on live animals to check it works in an organism and is safe
  • Then a small group of healthy volunteers is tested on, to check dosage and side effects
  • Then it is tested on a large group of people with the disease

This final trial is double blind to make sure the placebo effect doesn't come into play and the trial occurs to make sure it works for everyone

The results are also reviewed to prevent false claims

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Monoclonal Antibodies

A monoclonal antibody is a lymphocyte from a mouse mixed with a tumour cell

This produces a hybridoma which divides quickly, making lots ofidentical antibodies

These antibodies can bind to certain cells and are used to detect cancer and are in pregnancy tests

How a Pregnancy Test Works

  • Urine passes through the reaction zone
  • HCG hormone binds to HCG antibody in the zone
  • In the results window the HCG binds to the HCG monoclonal antibody (which are fixed on)
  • The other antibodies in the urine which don't bind to HCG will then bind to antibodies in the control zone
  • A blue dye appears in the control and results zone to show a positive test
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Plant Defences

Plants Need Ions Like :

  • Nitrates  - for making proteins and growth
  • Magnesium ions - for making chlorophyll

Plant Defences :

  • Leaves have waxy cuticles
  • Cell walls
  • Dead cells around stems
  • Some can produce antibacterial chemicals / poisons
  • Thorns
  • Leaves droop when something touches them

Plant Disease Symptoms :

  • Stunted or abnormal growth or malformed stems / leaves
  • Patches of decay or spots on leaves
  • Discolouration
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