A Level Biology Practice Exam 2025 - Free A Level Biology Practice Questions and Study Guide

The correct answer is characterized by the blood being enclosed in blood vessels, which is a defining feature of a closed circulatory system. In this type of system, blood circulates through a network of vessels, allowing for more efficient transport of nutrients, gases, and waste products compared to an open system. This arrangement enables higher blood pressure and more precise regulation of blood flow to different tissues.

The other options describe characteristics that do not align with a closed circulatory system. Specifically, blood that flows freely in an open space indicates an open circulatory system where blood is not confined to vessels. Direct contact of blood with body cells is also typical of an open system, where hemolymph bathes tissues directly. Lastly, the presence of a heart is essential in a closed system to pump the blood through the vessels, making the absence of a heart incompatible with this type of circulatory arrangement.