Planarians lack dedicated respiratory and circulatory systems. This deficiency does not cause a problem because ________.
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 have a highly branched gastrovascular cavity that allows for efficient gas exchange and nutrient distribution throughout their body since none of their cells are far from this system or from the external environment. This makes the lack of dedicated respiratory and circulatory systems not a problem for them.

Planarians Lack Dedicated Respiratory and Circulatory Systems