Which of the following statements regarding circulatory systems is true?
A) The smallest blood vessels in the body are veins.
B) A circulatory system is necessary in any animal whose body is too large or too complex for vital chemicals to reach all parts of the body by diffusion.
C) Materials are exchanged directly between the blood and body cells.
D) Veins carry blood away from the heart to body organs and tissues.

Question

Quizplus · Accepted Answer

A circulatory system is necessary in any animal whose body is too large or too complex for vital chemicals to reach all parts of the body by diffusion. This is because diffusion is only effective over short distances and larger, more complex bodies require a system to transport substances throughout the body. The smallest blood vessels in the body are actually capillaries, not veins. Materials are exchanged between the blood and body cells through capillaries. Veins carry blood towards the heart, not away from it.

Which of the Following Statements Regarding Circulatory Systems Is True