A plasmid that is attached to the cell membrane or integrated into the bacterial chromosome is called an episome (q.v.). Plasmids are extremely valuable tools in the fields of molecular biology and genetics, specifically in the area of genetic engineering (q.v.).
A gerund is a form of a verb used as a noun, whereas a participle is a form of verb used as an adjective or as a verb in conjunction with an auxiliary verb. In English, the present participle has the same form as the gerund, and the difference is in how they are used. When used with an auxiliary verb (is walking), it serves as a verb and is the present participle. When used as an adjective (a walking contradiction) it is also a participle.
A gerund is a verb form ending in -ing that functions in a sentence as a noun. Although both the present participle and the gerund are formed by adding -ing to a verb, note that the participle does the job of an adjective while the gerund does the job of a noun. Compare the verbals in these two sentences: