Biology - Microbes & Disease

Microbes, Pathogens and Disease

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Microbes, Pathogens and Disease

The term microbe includes viruses, bacteria, protozoa and certain fughi. A microbe is a living organism, which is too small to see with the naked eye. 

Microbes, which cause disease, are commonly known as germs but should be called pathogens. 

Since most microbes are too small to be seen by the naked eye, they are very difficult to measure. For example, Paramecium, a microbe, is a small animal but it is one of the largest common Protozoa. It can only just be seen without a microscope. 

Paramecium is about one-quarter of a millimeter long, so we cannot easily measure it in millimeters. Instead we use micrometers. 

100 micrometers = 1millmetre. 

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Micro-organisms that cause disease.

Micro-Organism       Order of size       Example of disease       Other notes


Virus                        1                         Chicken Pox, HIV          Cantseewithmicroscp

Bacteria                   2                         Pneumonia, T.B            Harmless.

Protozoa                  3                        Malaria, Yellow Fever    Damage redbloodcell

Funghi                     4                        Ringworm, Athlete's Foot 

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Defence Systems

Many microbes are harmless. Some can cause disease or infections if they get inside the body. Microbes that cause disease are called pathogens

My red blood cells help fight the microbes that cause disease. 

TB, and food poisoning are caused by bacteria.

Tetanus, Flu and AIDS are caused by viruses.

Ringworm and Athletes Foot are caused by Funghi.

After going to the toilet i should wash my hands to stop microbes getting onto my food.

I should cover my nose and mouth when i sneeze to stop droplets of water containing microbes going into the air for someone else to breathe in.

Medicine users should not share syringes (needles) to stop microbes in the blood of one person getting into the blood of the other.

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What was the purposeof the unopened Petri dish?

Control. Comparison to show what would have without adding any samples. It proves any bacteria growth came from the samples.


A shallow circular dish with a loose-fitting cover, used to culture bacteria or other microorganisms.

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Antibiotcs are chemicals, sometimes obtained from natrual products (e.g funghi). They are able to kill bacteria and therefore help you recover from an illness. 

The commonest known antibiotic is penicillin, which was discovered just before the Second World War nd prevented huge numbers of deaths from gangrene etc.

Antibiotics work very well against bacteria but do not work against viruses!

Your body has its own immune system. It's like an army which is ready to defend you against any army invasion by harmful bacteria. 

When bacteria come into your body, your body makes anti-bodies, which act like soldiers to search out and destroy the enemy.

Antibiotics are chemicals which can help your body win the battle by killing the harmful bacteria cells or stopping them from growing. 
They can recognise the enemy because the cells of bacteria are different to the cells in your body.

Once the bacteria have been killed, your body's immune system sets to work to clean up all the dead bacteria and get them out of your body. 

Antibiotics don't work against viruses because the virus gets into your own body cells and hides there - a bit like a soldier not being able to recognise the enemy because he isn't wearing the right uniform.

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Bacteria are very tiny single cell organisms, which can live anywhere - on and in bodies, in water, in the ground and on anything you can touch. You need a very powerful microscope to be able to see them.

They can grow anywhere they can find the food they need, which is everywhere that is not sterile (too clean for germs).
Most bacteria do not make you sick but some can cause lots of illnesses when they get into a body - illnesses like some ear infections, tonsillitis and food poisoning.
Some can cause health problems when they make a toxin (poison) that gets carried around the body and makes you sick.
If you get a cut and don't clean it, bacteria can make the place where you cut yourself sore, and can also spread to other parts of your body making you feel headachy, hot and sick, or even worse
Not all bacteria are the bad guys. Some bacteria live inside our bodies and help to digest food, make vitamins like vitamin K, and help to fight against other harmful bacteria.

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Bacterial Growth

Many foods have bacteria in them, which can breed ad make the foodgo bad unless the food is preserved in some way. 

Food preservation is the process of treating and handling food in such a way as to stop or greatly slow down spoilage while maintaing nutritional value, texture and flavor
Preservation ususally involves preventing the growth of bacteriafungi and othermicro-organisms, as well as retarding the oxidation of fats which causesrancidity.

Common methods of preserving food include dryingfreezingvacuum-packing[?]canningradiation-treatment and adding preservatives. Other methods that not only help to preserve food, but also add flavor, include pickling,saltingsmoking and curing.

The oldest method of food preservation is by drying, which removes moisture required for bacterial growth

  • Drying, especially fruits (an example is grapes. They become raisins or sultanas when dry)
  • Salting - meat and fish packed in layers of salt don't go bad
  • Pickling in vinegar or brine (salty water) - onions, gherkins, olives, some fish
  • Canning and bottling - fruits, vegetables, meats, soups
  • Freezing and freeze-drying - just about everything can be preserved this way
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Thank you for this peice of work it has helped me alot with my work


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