Question

describe the evolutionary adaption of the digestive tract of roundworms.

Answer 1

The evolutionary ancestors of roundworms had a bi-directional digestive system. In other words, they took in food, digested it, and distributed the nutrients through channels where they could be directly absorbed by tissues. Whatever waste was left over was expelled through the mouth. In other words, their digestive systems were just elaborate sacs.

Roundworms evolved to have a unidirectional digestive system. Food is taken in through the mouth, processed in a long tube where nutrients are absorbed into tissues (absorbed into blood and carried to tissues, once a circulatory system had evolved). The waste products are then expelled through an anus at the other end of the digestive system.

A unidirectional system is much more efficient than a bidirectional one. Instead of taking in food, digesting it, then expelling it, the unidirectional system uses an 'assembly line' approach. Instead of tying up the entire digestive system for one task at a time, it's possible to constantly take in food and process it.