AQA Biology AS unit 1: Disease and Immunity

Revision notes on 3.1.1 Disease and Immunity AQA AS Biology.

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Unit 1: Disease and Immunity
All infectious diseases are caused by microorganisms.
Interfaces with the environment
This is a surface that links the external environment with the internal environment of the body.
1. Skin ­ impenetrable layer. Microbes can only enter if the skin is broken.
2. Gas exchange system ­ this system has evolved to allow the exchange of CO2 and oxygen so it has a
thin membrane, a massive surface area and a very good blood supply. Unfortunately this makes it
easier for pathogens to enter.
3. Digestive system ­ this system has evolved to allow the entry by absorption of small nutrient
molecules into the blood making it an ideal interface for pathogens.
4. Reproductive and urinary system ­ pass through urethra.
1. Mucus layer ­ mucus makes it difficult for pathogens to penetrate.
2. Enzymes ­ these breakdown the pathogens before they get across the interfaces.
3. Acid ­ this is found in the stomach and it kills pathogens.
How are symptoms caused?
1. Damage host tissues ­ large numbers of pathogens prevent tissues from functioning properly. Many
breakdown cell membranes causing CELL DEATH. Some are able to inhibit DNA synthesis and protein
2. Produce toxins ­ bacteria produce toxins which are damaging to cells in many ways.

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Lifestyle and Health
There are a number of diseases that result from a person's lifestyle.
Is a measure of the probability that damage to health will occur as a result of a given hazard.
1. The probability that the hazard will happen.
2. The consequences of the hazard happening.
Risk factors for cancer in general
1. Smoking.
2. Excessive exposure to sunlight ­ using sunbeds and sunbathing without using sunscreen.
3. Excessive alcohol intake.
4. Diet.
5. Physical activity.
Risk factors for CHD
1.…read more

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Phagocytes ingest and destroy pathogens. Some phagocytes travel in the blood but can move out of blood
vessels into other tissues.…read more

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Specific immunity
Once an individual has experienced a particular species of pathogen it will fight off future infections by the
same pathogen much more quickly. The individual is said to have immunity to that pathogen.
All foreign cells have antigens on their surface.
Antigens are:
a) Proteins.
b) Part of cell membrane/cell wall..
c) They trigger production of antibodies
Cell mediated immunity
Antigen-presenting cells
When the body cells are invaded by pathogens the antigens of the pathogen become embedded in the cell
membrane.…read more

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Some stimulate B cells to divide.
d) Some kill infected body cells ­ they do this by releasing a protein that forms holes in the cell
membrane of the cells that have been infected.
Humoral response
Antibodies are transported in the blood and body fluids. Each type of B lymphocyte produces a different
type of antibody that responds to one specific type of antigen or toxin (these also act as antigens).
Pathogens have many different antigens on their surface.
B lymphocyte response
1.…read more

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Secondary response
1. Memory B cells divide into plasma cells (by mitosis) which secrete antibodies.
2. Memory T cells divide into the different types of T cells so they can destroy the cells that are
This response is QUICKER ­ greater concentration of antibodies = person does not usually show
symptoms.…read more

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The two antigen binding sites make agglutination (clumping together of pathogens) easier for the antibodies
to achieve. This interlocking of antibody and antigen blocks the active region of the antigen, rendering it
3. Agglutination also makes the pathogens easier to track down by the phagocytes.
4. The antibody-antigen complex stimulates the production of a plasma protein called complement, which is
capable of destroying pathogens, causing inflammation, and coating the pathogen, making it easier for the
phagocyte to ingest it.…read more

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Use an easily transportable and storable vaccine.
3. Use a vaccine with few side effects.
4. Have many trained staff to administer the vaccine.
5. Vaccinate all vulnerable individuals at the same time.
If for a certain time there are no individuals with the disease then transmission of the pathogen can be
interrupted and sometimes eradicated completely.
Why does vaccination fail to eradicate all diseases?
1. Some viruses have hundreds of different strains.
2. Some viruses show antigenic variability.
3.…read more

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Once the one is founded it is cloned to produce large amounts of required antibody.
1. To separate a chemical from a mixture.
2. Used in immunoassay ­ is a method for calculating the amount of substance in a mixture.
3. Cancer treatment ­ the antibodies are used to carry the cytotoxic drugs to the cancer cells.
4. Transplant surgery ­ monoclonal antibodies can reduce the chance of rejection by disarming T cells.
Arguments for
Used to treat cancer & diabetes.…read more


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