Which of the following accurately describes a closed circulatory system?

• A. The heart pumps blood into large sinuses where it mixes with interstitial fluid.
• B. Blood flows freely through body cavities, directly bathing organs.
• C. Oxygen is directly absorbed from the environment into the bloodstream without the use of lungs or gills.
• D. Blood is contained within vessels and circulates unidirectionally from the heart around the body.

Answer: (D)

Verified step by step guidance

1. Understand the concept of a closed circulatory system: In a closed circulatory system, blood is contained within a network of blood vessels, which allows for efficient transport of nutrients, gases, and waste products throughout the body.
2. Identify the key components of a closed circulatory system: These include the heart, which acts as a pump, and a series of blood vessels (arteries, veins, and capillaries) that form a closed loop.
3. Differentiate between open and closed circulatory systems: In an open circulatory system, blood is not confined to vessels and instead flows freely through body cavities, directly bathing organs. In contrast, a closed system keeps blood within vessels.
4. Analyze the given options: Evaluate each statement to determine if it aligns with the characteristics of a closed circulatory system. Look for descriptions that mention blood being contained within vessels and circulating in a controlled manner.
5. Select the correct description: The statement 'Blood is contained within vessels and circulates unidirectionally from the heart around the body' accurately describes a closed circulatory system, as it highlights the containment and directional flow of blood.