Q.51. Among the following, which best describes an organism that lives at the expense of other
organisms, harmful but usually not killing?
(A) Predator
(B) Symbiotic
(C) Prey
(D) Parasite

The correct answer to the multiple-choice question is (D) Parasite, as it precisely describes an organism that lives on or in another, deriving nutrients while harming but typically not killing the host.​

Question Breakdown

This MCQ tests ecological relationships in biology, focusing on interspecies interactions where one organism benefits at another’s cost.

Correct Answer: Parasite

A parasite lives in or on a host organism, obtaining nutrients or shelter, which harms the host but rarely kills it outright to ensure its own survival. Examples include lice on humans or tapeworms in intestines, weakening the host over time without immediate death.​

Option Explanations

• (A) Predator: Captures and kills prey outright for food, such as a lion hunting a zebra, directly causing death unlike the described relationship.​

• (B) Symbiotic: Involves close associations where symbiosis can be mutualistic (both benefit), commensal (one benefits, other unaffected), or parasitic (one harms), but the term alone does not specify harm without death.​

• (C) Prey: The organism hunted and consumed by predators, victim rather than exploiter, opposite of living at others’ expense.​

• (D) Parasite: Matches perfectly—benefits at host’s expense through harm (e.g., nutrient drain, disease) but sustains the host long-term.​