40. Circulatory System
Circulatory and Respiratory Anatomy
Multiple Choice
Multiple ChoiceWhy do larger animals, such as a bullfrog, require a circulatory system, while animals such as a planarian do not?
A
Each cell in a bullfrog requires more oxygen and nutrients than each cell in a planarian.
B
The cells of a bullfrog are many times larger than the cells of a planarian.
C
Gases do not diffuse through bone. Therefore, any animal with bones, such as a bullfrog, has to have a circulatory system. Any animal without bones, such as a planarian, does not have a circulatory system.
D
None of the choices is correct.
E
Diffusion is inadequate to move gases through the body surface and into all parts of a larger animal body. However, diffusion alone is sufficient to move gases in and out of the thin body of a planarian.
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