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4.1 Communicable Diseases

Organisms that cause disease
Pathogen ­ a microorganism that causes disease

Bacteria Fungi Virus Protoctista
> Belong to the > Common > Viruses invade > Protoctista
kingdom fungal cells and take over usually cause
prokaryotae infections the genetic harm by
> Smaller than are where machinery and…

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harbour pathogens e.g. HIV, bacterial Using condoms during intercourse
meningitis, athletes foot and ring worm
Faecal ­ oral transmission, usually by Treatment of waste water
eating/drinking water contaminated by the Treatment of drinking water
pathogen e.g. cholera Thorough washing of all fresh food
Careful food preparation and cooking
Droplet infection…

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Indirect transmission of plant pathogen occurs as a result of insect attack.

The fungus that causes Dutch elm disease is carried by the beetle Scolytus multistriatus.

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Plant Defences against pathogens
Passive Defences
Physical Defences
a) Cellulose cell wall ­ this acts as a physical barrier but also contains many chemical
defences that can be activated when a pathogen is detected
b) Thickening of the cell wall with lignin ­ lignin is a phenolic compound and
completely…

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Primary Defences against Disease

Primary defences are the defences in place that prevent pathogenic material from entering the
body.
The Skin
The skin is the main primary defence. The outer layer of skin is called the epidermis and consists of
layers of keratinocytes. The keratinocytes are produces at the base…

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Mucous Membranes






The epithelial layer contains mucussecreting cells called goblet cells and also mucus secreting
glands under the epithelium.

The mucus traps any pathogens that may be in the air
The epithelium is also ciliated

Cilia are tiny hairlike organelles that can move in a coordinated fashion to waft the…

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specialised receptors on their cell surface membranes. Antibodies are produced by B lymphocytes,
and these neutralise foreign antigens. Long term disease protection is provided. An immunological
memory is produced as B memory cells are released and circulate in the body for a number of
years.


1. Pathogen enters the body…

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B memory cells ­ cells that remain in the blood for a long time, providing longterm immunity

They are involved in the humoral response (producing antibodies)


Cell signalling

Macrophages release monokines which attract neutrophils (by chemotaxis ­ the movement of
cells towards a particular chemical) and stimulate differentiation of B…

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4x polypeptide chain, 2x light chains & 2x heavy chains
The tips of the y are the variable region but is the same for every type of antibody



Opsonins
A group of antibodies that bind to pathogen antigens and then act as binding sites for phagocytic
cells

Some are nonspecific…

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Antitoxins

Some antibodies bind to molecules that are release by pathogenic cells.
These molecules may be toxic and the action of antitoxins render
them harmless.






Primary and Secondary Responses
Primary immune response ­ initial response caused by a first infection

Secondary immune response ­ more rapid and vigorous response caused…

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