Communicable Diseases


Health and disease

Pathogens are disease causing micro-organisms. They can be viruses, bacterias, protists or fungi.

Communicable diseases are infectious. They can be caught.

A disease is the abnormal function of the body,

Health is a state of physical and mental well-being.

Factors including diet, stress and life situations can affect health.

Diet - not enough or too much - starvation, amaemia, diabetes, cancers.

Stress - mental health problems - heart disease, cancer, depression.

Life situations - fincancial status, where you live, gender - malaria.

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Pathogens and disease

Pathogens are microorganisms that cause disease. They can be bacteria, viruses, protists or fungi. They infect both animals and plants and cause a range of diseases.

Communicable diseases are caused either directly by a pathogen or by a toxin made by a pathogen. 

Bacteria are single-celled living organisms, smaller than animal and plant cells. They cause disease by rapidly splitting in 2 (binary fission) and they may produce toxins that make you feel ill. Sometimes they directly damage your cells.

Viruses are much smaller than bacteria, they cause diease on every type of living organism. They cause disease by taking over the cells in your body. They live and reproduce inside the cells, damaging and destroying them.

Pathogens are spread by air - droplet infection - common cold, flu

By direct contact - STD, plant infections - HIV/AIDS, tobacco mosaic

By water - fungal spores, dirty water - rose black spot, cholera

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Malaria is a disease caused by a protist, they are parasites which live and feed on living organisms. The life cycle of this protist includes time in the human body and the female mosquito.

The protist produces sexually in the mosquito and asexually in the human. The mosquitoes act like vectors of the disease.

The female lays her eggs in the human and this is when the protist is passed into the bloodstream. The protists travel around in the circulatory system and affect the kidney and damage red blood cells. It weakens the person and if it isn't treated, it can kill them.

Globally, around 660,000 people die from malaria every year. 

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Body defense responses

The Immune System:

White Blood Cells

  • Phagocytes ingest pathogens so they cannot make you ill.
  • Lymphocytes produce chemicals called antibodies which target particular bacteria or viruses and destroy them. 
  • Each pathogen needs a unique antibody for it to be destroyed. 
  • Once your WBC have produced this antibody, it can be made again very quickly if that pathogen enters your body again. This stops you from getting the disease twice.
  • Other white blood cells produce antitoxins which cancel out the toxins produced by the pathogen.
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Monoclonal antibodies

Monoclonal antibodies are produced from a single clone of WBC - B-lymphocyte.

To make monoclonal antibodies:

B lymphocytes can make specific antibodies, but they cannot divide. Tumour cells cannot make antibodies but the can divide. When they are combined, they become a hybridoma cell that can make specific antibodies and can also divide. These cells are then cloned and monoclonal antibodies are made. These monoclonal antibodies are then seperated and purified so that they can be used.

Monoclonal antibodies are used:

  • for diagnosis in pregnancy tests
  • in labs to measure levels of hormones and other chemicals in the blood to detect pathogens for research
  • to identify or locate specific molecules in cells or tissue
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Developing drugs

A good medicine is:

  • effective - prevent or cure
  • safe - not too toxic
  • stable - normal conditions
  • successfully taken/removed from body - reach target and be cleared from system

Researches target a disease and make lots of possible new drugs.These are then tested in a lab to find out if they are toxic and if they are efficient. In the lab, they are tested on cells, tissues and whole organs. Many chemicals fail.

The small amount of chemicals that pass the tests are then tested on animals to find out if they work on a living organism. It gives information about possible doses and side effects. Then scientists can predict how the drugs might behave in humans.

Drugs that pass animal tests move on to clinical trials on humans. Very low doses are given to healthy volunteers to check for side effects. If it's safe, it is tried on a small number of patients to see if it treats the disease. If the medicine passes all legal tests, it is licensed and can be prescribed. 

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Good resource  to revise from.



Good to revise for paper 1 GCSE

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