Which substance is essential for the formation of red blood cells and transport of oxygen?

Haemoglobin is an essential protein found in red blood cells that plays a critical role in the transport of oxygen throughout the body. It binds to oxygen molecules in the lungs and carries them to tissues and organs where they are needed. Additionally, haemoglobin helps facilitate the transport of carbon dioxide, a waste product, from the tissues back to the lungs for exhalation.

Without adequate levels of haemoglobin, the body cannot transport sufficient oxygen, leading to conditions such as anemia, which can cause fatigue and other health issues. Understanding this function underscores the importance of maintaining healthy levels of iron and other nutrients necessary for haemoglobin production. Other substances mentioned, like cholesterol and glucose, serve different roles in the body, such as energy provision or cellular structure, but do not directly contribute to the formation of red blood cells or their primary function of oxygen transport. Fibrinogen is involved in blood clotting rather than oxygen transport, further establishing why haemoglobin is the correct choice for this question.