IGCSE Biology: Pathogens, Diseases and Immunity

Vocabulary practice flashcards based on Cambridge IGCSE Biology notes covering pathogens, physical and chemical body defences, immune responses, vaccination, herd immunity, and cholera.

Pathogen

A disease-causing organism.

Transmissible disease

A disease caused by a pathogen that can be passed on from one host to another.

Direct contact transmission

Pathogen transmission where the disease is passed directly from one host to another by transfer of body fluids such as blood or semen.

Indirect contact transmission

Pathogen transmission where the pathogen leaves the host and is carried by an intermediate medium or vector, such as contaminated surfaces, air, food, water, or insects.

Mechanical barriers

Physical structures of the body, such as skin and nose hairs, that make it difficult for pathogens to enter the body.

Chemical barriers

Substances produced by body cells, such as mucus and hydrochloric stomach acid, that trap or kill pathogens.

Phagocytosis

The process carried out by a specific type of white blood cell of engulfing and digesting pathogenic cells.

Agglutination

The clumping together of pathogenic cells by antibodies, restricting their movement and signaling them for phagocytosis.

Active immunity

Slow-acting, long-lasting defence developed when the body produces its own specific antibodies and memory cells after infection or vaccination.

Antigen

A molecule, such as a protein, located on the surface of a cell membrane that can be recognised by lymphocytes.

Antibody

A protein made by lymphocytes that is complementary in shape to a specific antigen, attaching to pathogens to cause agglutination and signal destruction.

Antitoxin

A protein produced by the body that neutralises the toxins produced by bacteria.

Memory cells

Long-lasting cells produced during an immune response that retain instructions to quickly produce specific antibodies if the pathogen is encountered again.

Vaccination

The introduction of a dead or altered form of a pathogen into the body to provoke antibody and memory cell production without causing disease.

Herd immunity

Protection provided to an entire population when a sufficiently high percentage is vaccinated, preventing widespread transmission of contagious disease.

Passive immunity

Fast-acting, short-term defence against a pathogen acquired via antibodies from another individual (e.g., through breast milk), without making memory cells.

Diarrhoea

The loss of watery faeces from the anus, which can cause severe loss of water and ions from body tissues.

Oral rehydration therapy

A treatment for severe diarrhoea consisting of a drink with a small amount of salt and sugar dissolved in water.

Vibrio cholerae

The bacterium responsible for cholera that releases a toxin in the small intestine, causing chloride ions and water to enter the lumen and result in severe diarrhoea.