The correct answer is parasitism.
Parasitism, in the field of evolutionary biology, refers to an association between species, where the parasite, the organism, lives on or in another species, the host, creating some kind of harm in it, and is amended structurally to this way of life.
The parasites include protozoans, like as the agents of sleeping sickness, malaria, and amoeba dysentery; animals, like lice, hookworms, mosquitoes, and vampire bats; fungi, like the agents of ringworm, honey fungus; and plants, like dodder, mistletoe, and the broomrapes.