Final answer:
Pathogen A, with an ID50 of 50 particles, is the most virulent as it requires the fewest particles to infect 50% of a population. Alpha particles have the highest ionizing power but least penetration ability, and gamma rays are the most penetrating form of ionizing radiation.
Step-by-step explanation:
Among pathogens A, B, and C, the one most susceptible to damage is the one that has the lowest infectious dose 50 (ID50), which is the number of particles required to infect 50% of a test population. Pathogen A with an ID50 of 50 particles is the most virulent compared to pathogen B with an ID50 of 1,000 particles and pathogen C with an ID50 of 1 × 106 particles. Virulence is an indication of a pathogen's ability to cause disease; a lower ID50 implies higher virulence, meaning fewer organisms are needed to cause infection.
Gastrointestinal tracts are particularly vulnerable portals of entry for pathogens since microorganisms are constantly inhaled or ingested. To minimize damage from infections, practices such as regular handwashing, safe food handling, and vaccinations are important.
When discussing ionizing radiation, alpha particles have the highest ionizing power and greatest ability to damage tissue but are the least penetrating and can be stopped by a thick sheet of paper or a layer of clothes. However, if an alpha emitter is ingested or inhaled, there is significant risk. In contrast, gamma rays have the most penetrating power and can pass through most materials, thus requiring lead or concrete for effective shielding.