Second line of defence (Edexcel GCSE Biology Combined Science): Revision Notes

Second line of defence

Phagocyte (type of white blood cell)

They digest pathogens

Immune System

• White blood cells: travel everywhere in body in blood& patrol for pathogens
• B-Lymophocytes: type of blood cell involved in the specific immune response
• Antigen: on the bacteria
• Antibodies: produced by white blood cells

Antigens & antibodies

Antigens are found on cell membrane of pathogens and are specific to each species

How it destroys

• Punches holes in microbes
• Sticking them together so they cant move & can be engulfed by phagocyte

Produce Anti-Toxins

Toxins released that counteract the toxins produced by pathogen

Exposure to Pathogens:

Pathogens are microorganisms that cause disease, such as bacteria, viruses, and fungi.

• When a pathogen enters the body, it carries antigens on its surface. Antigens are unique molecules or proteins that the immune system can recognise as foreign.

Antigens Trigger an Immune Response:

Recognition of Antigens:

• The specific immune system recognises the antigens present on the pathogen.

• White blood cells called lymphocytes (a type of white blood cell) play a key role in identifying these antigens. Activation of Immune Response:

• Once a lymphocyte recognises the antigens, it activates and starts the immune response.

• The immune response is targeted specifically at the pathogen with these unique antigens.

Production of Antibodies:

What are Antibodies?:

Antibodies are proteins produced by a type of lymphocyte called B cells.

• Each antibody is specific to a particular antigen, meaning that it will only bind to and neutralise the pathogen that has that specific antigen. How Antibodies Work:

Once produced, antibodies bind to the antigens on the surface of the pathogen.

This can:

• Neutralise the pathogen, preventing it from harming the body.
• Mark the pathogen for destruction by other white blood cells (such as phagocytes) which engulf and destroy the pathogen.