What is the purpose of hemoglobin in red blood cells?

Hemoglobin serves a crucial role in red blood cells by absorbing and transporting oxygen throughout the body. This protein is specifically designed to bind with oxygen molecules in the lungs and release them in tissues that require oxygen for cellular processes. The presence of hemoglobin allows red blood cells to effectively carry oxygen from the lungs to the corresponding cells in various organs, enabling aerobic respiration and producing the energy necessary for bodily functions.

While carbon dioxide transport also occurs, it is not the primary function of hemoglobin; instead, it mainly facilitates the uptake of oxygen. The options concerning fighting infections and maintaining body temperature do not pertain to the direct function of hemoglobin, as these tasks are managed by other components of the immune and circulatory systems. Thus, the primary and irreplaceable role of hemoglobin is its ability to absorb and transport oxygen, which is essential for sustaining life.