Communicable diseases

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  • Created on: 01-05-16 12:29
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Esme Nias Pages 294296 16.3.16
Communicable diseases
These are diseases caused by infective organisms known as pathogens (including
bacteria, virus, fungi and protoctista)
These diseases can be passed on from one organism to another
In animals, they can not only be spread within species, but between species
Vectors carry the pathogens from one to another = water and insects
13 million people a year die from communicable diseases (23% of all deaths)
Types of pathogens:
A small proportion of these bacteria are pathogens that cause communicable
Bacteria are prokaryotes so their cell structure is different to the eukaryotic
organisms they infect
They do not have membrane bound organelles or a nucleus
Bacteria can be classified in two different ways
By their shape = rod shaped (bacilli), spherical (cocci), comma shaped
(vibrios), spiralled (spirilla), corkscrew (spirochaetes).
By their cell walls =
they react differently with gram staining
o Gram positive
bacteria are purpleblue under a
o Gram negative
bacteria are red
o This is useful as
it affects how the bacteria react to different antibiotics.
Non living infectious agents
50 times smaller in length than bacteria
They have some genetic material surrounded by a protein
They invade living cells where they reproduce rapidly and
evolve by developing adaptations to their host = successful
There are viruses that attack bacteria = bacteriophages
Group of eukaryotic organisms that have a variety of feeding
They are cells grouped into colonies

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Esme Nias Pages 294296 16.3.16
The protists which cause disease are parasitic = they use people or animals as
their host organism
They need a vector to transport them to their host (malaria) or they may enter
through polluted water
Mainly a problem in plants
Eukaryotic organisms that are multicellular
Fungi cannot photosynthesis and they digest their food extracellularly before
absorbing the nutrients.
Some are parasitic
They infect the leaves of plants and stop them photosynthesising so the plant
quickly dies.…read more


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