Which element is essential for the construction of hemoglobin?

Hemoglobin is a complex protein found in red blood cells that is responsible for transporting oxygen from the lungs to the body's tissues and returning carbon dioxide from the tissues back to the lungs. The key component of hemoglobin is iron, which plays a vital role in its structure and function. Each hemoglobin molecule contains four iron atoms, which are bound to a heme group. This iron is critical for oxygen binding; it can form a reversible bond with oxygen molecules, allowing hemoglobin to effectively pick up oxygen in the lungs and release it in the tissues where it is needed.

The presence of iron is what allows hemoglobin to carry oxygen, and without sufficient levels of iron, the body cannot produce enough healthy red blood cells or hemoglobin, which can lead to iron-deficiency anemia. Therefore, iron is essential for the construction and proper function of hemoglobin, making it the correct answer to the question.