Complete the following paragraph. Fetal hemoglobin is essential for the survival of placental animals because Hb F has a affinity for O2 at oxygen partial pressures found in the placenta as compared to the oxygen affinity of Hb A. This difference in affinity for O2 allows O2 from the hemoglobin in the to transfer to the hemoglobin in the .

The Oxygen (O2) from Hemoglobin A from the bloodstream is transferred to Hemoglobin F in the placenta due to its higher affinity for Oxygen (O2).

Explanation:

Hemoglobin is a metalloprotein that binds to Oxygen (O2) using its central Iron (Fe) atom which is bound to the heme group.

Hemoglobin A is glycated hemoglobin found in the bloodstream. It functions primarily in the Oxygenated red blood cells. There it carries Oxygen to the various tissues. Due to the coupled monosaccharide (usually glucose), it has less affinity for oxygen and would easily release its bound oxygen to a molecule with higher affinity.

Hemoglobin F found in the placenta is the Hemoglobin found in the placenta during pregnancy and for a few weeks after birth. It has a higher affinity for Oxygen and would readily attract Oxygen from Hemoglobin A due to its lack of bonding with any sugar particularly 2,3-bisphosphoglycerate (2,3-BPG or 2,3-DPG).

This difference allows the fetus to access oxygen optimally from the mother's oxygenated hemoglobin.

Hence the statement is best comleted as such "This difference in affinity for Oxygen (O2) allows Oxygen (O2) from the hemoglobin A in the bloodstream to transfer to the hemoglobin F in the placenta".