symbiosis
/ˌsɪmbɪˈəusɪs, -baɪ-; ˌsɪmbɪ`osɪs, -baɪ-/ n[U](biology 生) relationship between two species, organisms,etc that live close together and depend on each other in various ways 共生（关系）
the symbiosis between a plant and the insect that fertilizes it 一植物与使其受精昆虫的共生关系.