Planarians lack dedicated respiratory and circulatory systems 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


A

Biology & Microbiology

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Saltatory conduction is a term applied to the "jumping" movement of action potentials

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Contact transmission may occur indirectly when a nonliving intermediate called a _______ is involved

Fill in the blank(s) with the appropriate word(s).

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