Which statement about hemoglobin is NOT true?

Hemoglobin is a protein complex in red blood cells that plays a crucial role in transporting oxygen from the lungs to the tissues and facilitating the return transport of carbon dioxide from the tissues back to the lungs.

The statement regarding hemoglobin's affinity for oxygen and carbon monoxide is significant because carbon monoxide binds to hemoglobin with a much greater affinity than oxygen—about 200 to 250 times greater. This means that, under physiological conditions, if carbon monoxide is present, it can effectively compete with oxygen for binding sites on hemoglobin, leading to decreased oxygen transport in the bloodstream.

Analyzing the other statements, hemoglobin is indeed responsible for the transport of oxygen (the first statement), consists of two alpha and two beta chains (the second statement), and contains iron heme groups that successfully bind oxygen (the fourth statement). Each of these features is an established characteristic of hemoglobin that supports its role in gas transport in the body. Thus, the claim that oxygen has a higher affinity than carbon monoxide is not true, making it the correct response to the question.