OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

How does oxyhemoglobin differ from hemoglobin?

1. It is dark red in color

2. It binds with carbon dioxide

3. It carries oxygen and is bright red

4. It is produced in the bones

The correct answer is: It carries oxygen and is bright red

Oxyhemoglobin is a form of hemoglobin that has bound to oxygen molecules, and its primary function is to transport oxygen from the lungs to tissues throughout the body. When hemoglobin binds with oxygen, it undergoes a structural change that allows it to absorb light differently than its deoxygenated counterpart. This change in structure leads to oxyhemoglobin being bright red in color, which is why arterial blood is often referred to as bright red due to its oxygenated state. The other choices describe features that do not apply specifically to oxyhemoglobin. For instance, while hemoglobin can bind with carbon dioxide, oxyhemoglobin itself primarily carries oxygen and does not focus on carbon dioxide transport. Similarly, the statement about color being dark red refers more to deoxygenated hemoglobin, which is indeed darker. The mention of production in the bones is irrelevant since hemoglobin is produced in the bone marrow as part of red blood cell synthesis, but it does not describe a difference between oxyhemoglobin and hemoglobin. Thus, the correct understanding is that oxyhemoglobin is characterized by its bright red color due to its oxygen content.