Kaplan Nursing Entrance Exam Practice 2026 – Comprehensive Prep

The term 'closed circulatory system' refers to a physiological system in which blood is confined within blood vessels at all times. This structure allows for more efficient transport of nutrients, gases, and waste products. In a closed circulatory system, the movement of blood is regulated and controlled, enabling organisms to maintain higher blood pressure and direct blood flow to specific tissues and organs as needed.

In contrast, systems where blood flows freely in open body cavities allow for less efficient circulation and lack the same degree of control over blood distribution. The other options present scenarios that do not involve the principles of a closed circulatory system, such as a lack of blood or a focus on air movement rather than blood circulation. Therefore, recognizing that blood is contained within vessels characterizes the closed circulatory system and its crucial role in the functioning of various organisms, especially those that require sophisticated internal transport mechanisms.