What is the primary function of hemoglobin in the body?

Hemoglobin plays a crucial role in the body primarily by transporting oxygen from the lungs to various tissues and organs. This protein is found in red blood cells and is essential for facilitating the delivery of oxygen to cells, where it is used for cellular respiration and energy production. Hemoglobin binds oxygen in the lungs, where the concentration is high, and releases it in areas where the concentration is lower, ensuring that all body tissues receive the oxygen they need to function properly. This effective transport mechanism is vital for sustaining life, as oxygen is a key element required for metabolic processes.

The other choices provided do not align with the primary functions of hemoglobin. For instance, while glucose transport is important for energy delivery, it is carried out by other mechanisms, such as glucose transporters in the bloodstream. Muscle building involves different processes like protein synthesis and is not directly related to hemoglobin's function. Lastly, temperature regulation is managed through various physiological processes, including sweating and blood flow regulation, rather than through hemoglobin activities.