35. Hemoglobin is a protein responsible for oxygen transport in the blood. Which of the following best describes the role of the metal ion in hemoglobin's function? (A) The metal ion provides structural stability to the protein by forming disulfide bonds between different subunits. (B) The metal ion acts as a cofactor, directly catalyzing the binding of oxygen to the protein. (C) The metal ion directly binds oxygen, facilitating its transport from the lungs to the tissues. (D) The metal ion regulates the pH of the blood, indirectly influencing oxygen binding to hemoglobin. (E) The metal ion is involved in the synthesis of heme, a prosthetic group essential for hemoglobin function.