Question

Platyhelminthes, like the flatworm seen here, do not have a respiratory system. All but one of the statements explains why this is possible. That is they A) are anaerobic organisms. B) live in a moist/aquatic environment. C) have a high surface area:volume ratio. D) have a thin body that facilitates diffusion throughout.

Answer 1

B) Live in a moist/aquatic environment
Organisms that live in aquatic environments also require respiratory systems if their bodies are too large in to allow for diffusion to be a sufficient mechanism for gaseous exchange. An example is the fact that fish have gills which make up their respiratory systems, even though they live in aquatic environments.