Question

Roundworms are round. Is a round shape a better or worse shape for diffusion compared to a flat shape? If the basic body design of an animal like the roundworm in not good for diffusion, how do they solve the problem of transporting nutrients and waste products around the body?

Answer 1

Nematodes have a complete digestive system. Complete digestive systems are seen in more complex organisms and offer many advantages. An animal with complete digestive system has both mouth and anus. As the food moves along the digestive tract by peristalsis it is broken down to molecules and absorbed by the cells lining the tube. Indigestible wastes pass out through the anus.

Nematodes are slender, and they are covered by cuticle, a waxy covering secreted by the epidermis. Because of this covering, gas exchange cannot occur directly across the skin like platyhelminths do. Gas exchange and waste excretion in nematodes occurs by diffusion across the wall of the gut. The nematodes are considered as pseudocoelomates.