Question

what makes up the double membrane found around both the mitochondria and plastids? the original membrane of the plastid and an outer membrane from the host cell both membranes are original to the plastid

Explanation:

According to the endosymbiotic theory, mitochondria and plastids (such as chloroplasts) are thought to have originated from free - living prokaryotes that were engulfed by a host cell. The inner membrane is the original membrane of the endosymbiont (plastid or mitochondria), and the outer membrane is derived from the host cell during the process of endocytosis.

Answer:

the original membrane of the plastid and an outer membrane from the host cell