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
The correct option is (A) None of their cells are far removed from the gastrovascular cavity or from the external environment.
Why Planarians lack respiratory and circulatory system?
Although planarians don't appear to have any respiratory or circulatory systems, they do have muscles that line the interior of the body in circular, diagonal, and longitudinal patterns.
The flatworm doesn't have lungs, therefore it doesn't require a particular circulatory system like a human does to move oxygen throughout its body.
Through its skin, the flatworm merely diffuses oxygen. Anywhere that it would want oxygen, this happens.
None of the cells of planarians are a great distance from the gastrovascular cavity or the outside environment, hence they lack specialized respiratory and circulatory systems.
Learn more about the Planaria with the help of the given link:
