What is Parasitism?

• A. A relationship in which both species benefit
• B. A relationship between two organisms of different species where one benefits and the other is harmed
• C. A relationship where populations interbreed
• D. A relationship where two species compete for resources

Answer: (B)

Parasitism is a relationship between two organisms of different species in which one benefits at the expense of the other. The parasite uses the host to obtain resources or a habitat, gaining nutrition or shelter, while the host suffers costs such as reduced nutrition, energy, or health. This can persist over time, with the parasite often not immediately killing the host but impacting its fitness. This differs from mutualism, where both species benefit, and from competition, where both are harmed by using the same limited resources. It’s also not about populations interbreeding, which describes gene flow rather than an ecological interaction. A common example is a tapeworm in a mammal’s intestine, which siphons nutrients from the host while the host bears the cost.