B1.1.2 How our bodies defend themselves against diseases

  • Created by: Fiona S
  • Created on: 20-04-15 00:52

Bacterial Cell


  • Bacterial cells are smaller than animal and plant cells
  • Bacteria do not have a nucleus
  • They have 2 types of DNA: Chromosal and Plasmid
  • Antibodies can kill selected bacteria, not the cells in your body

Bacteria are fought off by our body and the white blood cells. Our body changes conditions to kill the infection and reduce toxins.

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Virus Cell


  • Viruses are often considered non-living as they exist in an inert state outside of a host cell
  • Antibiotics do not work beacuse viruses are not alive
  • A virus is just a piece of DNA (or RNA)

Viruses latch onto our cells and use our cells material to reproduce, this can destroy our cells.

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Bacteria vs. Viruses


Size: Smaller than most plant & animal cells, but bigger than a virus.
Reproduction: Reproduce rapidly by binary fission (splitting in 2), providing have correct temp/nutrients etc.
Structure: Cytoplasm; Cell Membrane; Cell Wall and no distinct nucleas.
Genetic Material: Have one circular chromosome in the cytoplasm - does not have a distinct nucleus. (Some have additional small circles of DNA called plasmids.)
Examples: Tonsilitis, Ear Infection, TB, Syphilis.


Size: Smaller than bacteria.
Reproduction: Reproduce rapidly inside suitable host cell, cause they are acellular (needs a host cell).
Structure: Not a cell. Very simple structure. Protein coat, surrounding a few genes.
Genetic Material: Only has a few genes - usually linear pieces of genetic material.
Example: Flu; Common Cold; Herpes; Cold Sores; STI and HIV.

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  • Semmelweiss worked in Vienna General Hospital in the 1840s and witnessed large numbers of women dying after childbirth from childbed fever.
  • He thought that the staff of the hospital were spreading the disease via unwashed hands.
  • All medical doctors and students go straight from handling corpses, who had childbed fever, dead mothers, to delivering babies.
  • After instructing doctors and nurses to wash their hands in an antiseptic solution, the mortality rate was considerably reduced.
  • Although Semmelweiss didn't realise it at the time, the antiseptic solution was killing the infecting bacteria.
  • Apparently, when he left the Vienna hospital, the practice of washing hands in the antiseptic solution was relaxed, and the death rates rose again!
  • With the advent of new strain of bacteria today, there is now an even greater emphasis on hospital hygiene than ever before - so, if on a hospital visit, PLEASE WASH YOUR HANDS in the antiseptic gel provided.
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pathogen is a microrganism that cause illness or disease. Examples of a pathogen are bacteria and viruses. They may reproduce rapidly inside the body and may produce poisons (toxins) that make us feel ill. 

Fungi are also pathogens and includes microorganisms like yeasts and moulds

Viruses replicate by invading a cell and using the cell's genetic machinery to reproduce themselves i.e. copies of the original virus.

The virus 'invaded' cell then bursts releasing lots of new viruses.

The cell damage makes you feel ill as your body (temporarily) fights back to make as many good cells as it can to replace those destroyed by the virus.

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How do Pathogens enter the body?

Infection Type: Droplet Infection
How does it enter the body: By Coughing, Sneezing
Examples: Cold, Flu and TB

Infection Type: Direct Contact
How does it enter the body: Touch - Skin to skin
Examples: Chicken Pox, Conjunctivitus, STI/STD and Scabes

Infection Type: Contaminated Food and Drink
How does it enter the body: Food prepared in contaminated water, Consumtion, Raw meat or mouldy food
Examples: Cholera, Salmonela, Diahorea

Infection Type: Through a break in skin
How does it enter the body: Bites, ezcema, cut get infected, scratches, needle puncture wounds
Examples: Rabies, Maleria, Hepititus, HIV, Tetanus

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Defence Mechanisms

  • Skin
    • The forms an outer barrier to infection. Prevents infection entering body
  • Eyes
    • The eyes produce tears, which contain a natural antiseptic
    • Lysozyme enzyme - digest bacteria
  • Platelets
    • Found in blood and clots to form scabs
    • Platelets is a scab stuck in a fibrin(protein) mesh
  • Stomach
    • Hydrochloric Acid in the stomach destroys many microbes
  • Mucus & Cilia
    • Mucus traps dust and microbes and it is carried sweeped along the cilia
    • Mucus secreted into windpipe by goblet cells
    • Cilia sweep to top of throat. Cilia can stop sweeping by air infections/pollutions e.g. smoking. And inceases risk of infection
  • Ears
    • Wax
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White Blood Cells

Role: Ingesting Microbes

  • Some white blood cells ingest (take in) pathogens, destroying them so they can't make you ill.

Role: Producing Antibodies

  • Some white blood cells produce special chemicals called antibodies. These target particular bacteria or viruses and destroy them. You need a unique antibody for each type of pathogen. Once your white cells have produced antibodies once against a particular pathogen, they can be made very quickly if that pathogen gets into the body again

Role: Producing Antitoxins

  • Some white blood cells produce antitoxins. These counteract the toxins released by pathogen
  • Lymphocytes produce antibodies, antitoxins and memory cells
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  • Vaccination - Innoculation: taking a vaccine as a precaution against contracting a disease
  • Immunisation - the act of making immune (especially by inoculation)
  • Immunity - the ability of an organism to resist a particular infection of toxin by the action of specific antibodies or sensitised white blood cells
  • Antigen - a toxin or a foreign substance which induces an immune response in the body, especially the production of antibodies
  • Antibody - a blood protein produced in response to and counteracting a secific antigen. Antibodies combine chemically with substance which the body recognises as alien, such as bacteria and foreign substance in the blood

A vaccine usually contains:

  • Dead form of the pathogen
  • Antigens from the pathogen
  • A weakened or inactive form of the pathogen
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The immune response is stimulated in the body by antigens. These are proteins on the surface of cells. The antigens on microbes that enter the body are foreign to the antigens on our own cells. The immune system recognises that they are different.

There are 2 types of white blood cells involved in immunity. Lymphocytes produces antibodies. Phagocytes recognises cells labelled with antibodies and engulf and destroy the pathogen.

After they have recognised a foreign antigen the white blood cells reproduce to make some cells that begin producing antibodies, and some cells that 'remember' the antigen - these are called memory cells. If the same pathogen is encountered again, the memory cells can make the same type of antibodies very fast. So you become immune to the disease.

The first time you catch a new pathogen you become ill. There is a delay while the body produces the right type of antibody. 

The next time, the body's immune response should be able to destroy the pathogen before it makes us ill.

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Pro's and Con's of Immunisation for MMR


  • Prevents measles, mumps and rubella
  • Quicker and easier than single vaccines
  • You will be better protected against common symptoms such as rash, high fever, red and painful eyes, swollen glands and joint pain
  • You will be better protected against serious complications of these disease such as inflammation of the pancreas (pancreatitis) or imflammation of the brain (encephalitis)
  • If there is an outbreak of MMR then you can stay in work/school
  • Small pox and Polio eradicated
  • Save money and lives
  • Quick and free
  • 95% effective
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Pro's and Con's of Immunisation for MMR


  • Thought to cause autism and bowel cancer
  • Can cause a mild form of mumps or measles for up to 3 days afterwards
  • Could cause seizures brought on by high temperatures
  • May have some localised swelling
  • Have non-infectious rash, mild cold
  • Brain damage - risk very low
  • Naturally immune - lasts longer
  • Loads of people don't like needle
  • Repeat injections
  • Not everyone can have injection - allergies
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Uncontaminated Cultures of Microorganisms

For this:

  • Petri dishes and culture media must be sterilised before use to kill unwanted microorganisms.
  • Inoculating loops used to transfer microorganisms to the media must be sterilised by passing them through a flame.
  • The lid of the Petri dish should be secured with adhesive tape to prevent microorganisms from the air contaminating the culture.

In school and college laboratories, cultures should be incubated at a maximum temperature of 25°C, which greatly reduces the likelihood of growth of pathogens that might be harmful to humans.

In industrial conditions higher temperatures can produce more rapid growth of unwanted, potentially harmful microorganisms. E.g 37°C as it is the optimum tamperature for enzymes.

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Antibiotic Resistance

  • Many strains of bacteria, including MRSA, have developed resistance to antibodies as a result of natural selection.
  • To prevent further resistance arising it is important to avoid over-use of antibiotics.

Bacterial diseases can be treated by antibiotics but viruses cannot be treated with antibiotics because viruses live by invading our cells so to kill the virus you would have to kill the cells.

If antibiotic are used too often, or you don't take the full course of medicine prescribed by your doctor more resistant bacteria will survive.
If they go on to make someone else ill, they will not be killed by the original antibiotic.

They are resistant to that antibiotic. This is a result of genetic mutation (an example of natural selection).

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A mutation is an altration in the DNA.

Mutations are caused by:

  • Spontaneity
  • Radiation e.g. pollution
  • Carconagenic e.g. Cigarette smoke
  • Enviromental factors

There could be no consequences to a mutation. On the other hand, a mutation could be life threatening/lethal or even advantageous.


Peppered Moth and Spleckled Moth (Advantageous)

Cancer Mutation (Lethal)

Birth Mark of Freckles (Nothing)

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Antibiotic Resistance

To avoid this:

  • Antibiotics should only be prescribed when needed
  • Patients should finish the complete course of antibiotics
  • Introduction of infection control in hospital


is... Methicillin-Resistant Staphlococcus Aureus

The spread of MRSA can be prevented by:

  • Medical staff washing hands between patients (Semmelweiss)
  • Visitors are encouraged to wash hands before entering wards
  • If patients are affected they are isolated
  • Hospitals kept constantly clean
  • Medical staff disposable clothing
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