Key Stage 3 (KS3) Biology Practice Test

The circulatory system's main function is to transport blood throughout the body. This system consists of the heart, blood vessels, and blood itself. The heart pumps oxygen-rich blood from the lungs through the arteries to all parts of the body, delivering essential nutrients and oxygen to cells. In return, the blood collects carbon dioxide and other waste products from the cells and transports them back to the heart and lungs for removal from the body. This continuous flow is vital for maintaining homeostasis and supporting the various functions of other organ systems.

In contrast, the respiratory system is primarily responsible for the exchange of gases, particularly oxygen and carbon dioxide, while the digestive system focuses on breaking down food and nutrients for absorption into the bloodstream. The endocrine system regulates bodily functions through hormones but does not play a direct role in blood transport. Understanding the specific functions of each organ system helps clarify the essential role the circulatory system plays in overall health and function.