Which of the following statements best explains how planarians can survive and thrive without respiratory or circulatory systems?
A) none of their cells are far removed from the gastrovascular cavity or from the external environment
B) they lack mesoderm as embryos and, therefore, lack the adult tissues derived from mesoderm
C) their flame bulbs can carry out respiratory and circulatory functions
D) their body cavity, a pseudocoelom, carries out these functions

Question

Quizplus · Accepted Answer

Planarians can survive without specialized respiratory or circulatory systems because their flat bodies allow all cells to be in close proximity to the external environment or the gastrovascular cavity, facilitating direct diffusion of gases and nutrients.

Which of the Following Statements Best Explains How Planarians Can