Question

Regarding complexity of digestive system in animals: 1. An incomplete digestive system has single opening to the outside of the body that serves as both mouth and anus. 2. A complete digestive system has two openings, mouth and anus.

Answer 1

In animals: Organ systems in different groups of animals exhibit various patterns of complexities. For example, the digestive system in Platyhelminthes has only a single opening to the outside of the body that serves as both mouth and anus, and is hence called incomplete. A complete digestive system has two openings, mouth and anus