An open circulatory system __________.

• A. is less common in crabs and beetles than in mice and snakes
• B. unlike a closed circulatory system, does not rely on muscle contraction
• C. restricts the backflow of blood by valves in the trachea
• D. has no valves
• E. allows interstitial fluid to mix freely with vascular fluid

Answer: (E)

Verified step by step guidance

1. Understand the difference between open and closed circulatory systems. In an open circulatory system, the blood (or hemolymph) is not confined entirely to vessels and can mix with interstitial fluid, whereas in a closed circulatory system, blood is confined to vessels and is separate from interstitial fluid.
2. Recognize that open circulatory systems are common in many invertebrates, such as arthropods (including crabs and beetles) and mollusks, rather than in vertebrates like mice and snakes.
3. Note that in an open circulatory system, the heart pumps hemolymph into the body cavity, where it bathes the organs directly, allowing for the exchange of nutrients and waste products.
4. Understand that muscle contractions can still play a role in circulating hemolymph in an open circulatory system, but the system is generally less efficient than a closed system in terms of nutrient and gas exchange.
5. Identify that the key characteristic of an open circulatory system is the free mixing of interstitial fluid with vascular fluid, which is not the case in a closed circulatory system where blood is kept separate from interstitial fluid.