Answer: When enough people in a population are immune that the pathogen cannot spread efficiently, protecting even unvaccinated individuals.
- A A specific form of collective immunity that develops mainly within domesticated farm animal populations during normal conditions
- B When enough people in a population are immune that the pathogen cannot spread efficiently, protecting even unvaccinated individuals
- C A form of immunity that is sometimes thought to be acquired specifically through eating particular nutrient-rich foods as generally observed
- D A specialized type of passive immunity that some believe is transferred directly between family members in typical laboratory settings
Correct answer: B. When enough people in a population are immune that the pathogen cannot spread efficiently, protecting even unvaccinated individuals
Explanation: Herd (population) immunity: when a sufficient proportion of a population is immune (by vaccination or past infection), transmission chains break and even non-immune individuals are protected. Threshold varies: measles requires ~95% immunity; polio ~80-85%.
An antibody is Y-shaped, with two identical antigen-binding sites at the tips of the variable regions - each shaped to recognise one specific antigen - while the constant (Fc) region at the base is recognised by immune cells to trigger further responses.
Concept context
Innate and adaptive immunity, B cells, T cells, antibodies, vaccines, and immune disorders. Critical for NEET.