Antigens & Antibodies | Biology for GCSE/IGCSE - Year 11 PDF Download

Antigens & Antibodies: Extended

• Every cell possesses molecules, including proteins, that extend from their cell membranes.
• These molecules are called antigens.
• Individuals have unique antigens on their cell surface membranes.
• Lymphocytes can detect foreign antigens, such as those on pathogens within the body.
• When foreign antigens are recognized, lymphocytes produce antibodies that are complementary in shape to the antigens on the pathogenic cell's surface.

Lymphocytes producing antibodies diagram

The role of antibodies

• Antibodies have the capability to bind to antigens, leading to the agglutination of pathogens.
  • Agglutination inhibits the mobility of pathogenic cells.
• Simultaneously, chemicals are released to alert phagocytes of the presence of pathogens.
• Phagocytes then migrate towards the infection site, where they engulf and eliminate pathogens.
  • Agglutination facilitates the engulfment of multiple pathogens simultaneously.

Phagocytes and agglutination diagram

Immunity

• Upon encountering a pathogen for the first time, lymphocytes undergo an initial response, which may take several days, often resulting in illness.
• Following the initial encounter, lymphocytes can generate memory cells that preserve the blueprint for producing specific antibodies.
• Consequently, upon subsequent exposure to the same pathogen, antibodies can be swiftly produced and in larger quantities, preemptively destroying pathogens before they proliferate and cause sickness.
  • This mechanism accounts for how individuals develop immunity to certain diseases after a single infection.
• It's important to note that this mechanism isn't effective against all disease-causing microorganisms, particularly those that undergo rapid mutation, altering the antigens on their cell surfaces.
  • Consequently, if these mutated pathogens invade the body again, the memory cells from the initial infection may not produce antibodies that effectively match the new antigens.