A Level Biology Practice Exam 2025 – 400 Free Practice Questions to Pass the Exam

During the first circulation in a double circulatory system, blood is pumped to the lungs. In this system, also known as pulmonary circulation, deoxygenated blood is transported from the heart to the lungs via the pulmonary arteries. Once in the lungs, carbon dioxide is released from the blood, and oxygen is absorbed. This process is crucial because it replenishes the oxygen levels in the blood, preparing it for the next phase of circulation, where the oxygenated blood returns to the heart and is subsequently pumped to the rest of the body.

The other options are part of the broader circulatory process but do not describe the first circulation phase specifically. For instance, oxygenated blood being delivered to tissues occurs after the blood has been oxygenated in the lungs. Deoxygenated blood returning to the heart is part of both pulmonary and systemic circulation, but it is not what characterizes the first circulation phase. Nutrient absorption into the bloodstream is primarily associated with the digestive system and is not a primary function of the first circulation in the double circulatory system.