Biology AS Unit 1 Section 1

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Pathogens cause infectious diseases 

3 Main entries

  • Gas exchange- breathe in
  • Skin- broken skin
  • Digestive sysytem- eat/drink

Causes diseases by producing toxins and damagin body cells.

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The immune system

Antigens on the surface of the cell on the pathogen are identified as foreign. This activates the immune system.

Phagocytes engluf pathogens. Lysosomes fuse with the pathogen and the enzymes with it break it down.

The phagocytes activate the T cells

Some activae B cells and others kill the cell

The B cells divide into

  • Plasma cell that make antibodies 
  • Memory cells that remember the pathogen

Each B cell has a different shaped antibody.

The B cell secrete antibodies that coat the pathogen making it easier to engulf.

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Primary response

  • The antigen enters and activates the immune system.
  • The response is slow
  • The body starts to show systems

Afterwards the t and b cells produce memory cells so if the pathogen enters again the body is now immune.

Secondary response

  • The immune system is quicker
  • Memory cells turn to plasma cells and produce antibodies
  • T cells divide and killl the pathogen.
  • The body shows no symptoms
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The vaccine develops immunity so when we get the disease the body will already be immune.

Vaccines contain antigens that cause the body to produce memory cells. The body can become immune without showing symptoms. 

There are then less people the get the disease from; this is herd immunity

It is better for the vaccine to be injected than taken orally because there are enzymes in the mouth that could break it down.

The antignes on the pathogen activate the primary response. When the body gets infected for a second time you will not get ill.

However some pathogens can change their surface antigens - Antigenic Variation

You can suffer from the disease twice because it will be a different strain of the disease.

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Monoclonal antibodies

They are used to target specific substances or cells.

They are produced from a group of identical B cells

Their uses : Cancer

  • Cancer cells have antigens
  • Monoclonal antibodies are made to bind to the tumour. 
  • The drug will only accumulate where the cancer is

Example 2 : Pregnancy tests

  • They detect human chorionic gonadotropin (HCG) That is present it women's urine
  • The HCG will bind to the antibody (antigen-antibody complex)
  • If HCG present the strip turns blue if there is no HCG it wont bind and won't change colour
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Ethical issues


  • Testing on animals
  • Testing on humans
  • Testing on children
  • Side affects
  • Some people choose not to have the vaccine
  • Epidemic- If there was a rush to get the vaccine who would receive it first?
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