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
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Homologous chromosomes are:
A. a pair of chromosomes that match in size. B. a pair of chromosomes that match in appearance. C. a pair of chromosomes that have the same genes in the same position. D. All of the answer options are correct. E. None of the answer options is correct.
Saltatory conduction is a term applied to the "jumping" movement of action potentials
A. from one neuron to another. B. along the postsynaptic membrane from dendrite to axon hillock. C. along myelinated axons. D. across electrical synapses. E. in two directions at the same time.
Which of the following appeared last in the evolutionary timescale?
Contact transmission may occur indirectly when a nonliving intermediate called a _______ is involved
Fill in the blank(s) with the appropriate word(s).