Parasitism - GCSE Biology Definition

Parasitism is a type of relationship between two organisms where one, called the parasite, benefits at the expense of the other, known as the host. The parasite often lives on or inside the host and takes nutrients, usually causing harm. An example of parasitism is a flea on a dog: the flea feeds on the dog’s blood for food and energy, while the dog may suffer from irritation or disease. Parasitism is different from mutualism because only the parasite benefits and the host is harmed.