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.
Don't mistake a present participle phrase for a gerund phrase. Gerund and present participle phrases are easy to confuse because they both begin with an ing word. The difference is the function that they provide in the sentence. A gerund phrase will always behave as a noun while a present participle phrase will act as an adjective. Check out these examples: Walking on the beach, Delores dodged jellyfish that had washed ashore.