Biological Systems MCAT Practice Exam

What enables myofibers to store a quick reserve of oxygen?

1. Creatine phosphate

2. ATP

3. Myoglobin

4. Hemoglobin

The correct answer is: Myoglobin

Myofibers, or muscle fibers, have a unique protein called myoglobin that enables them to store a quick reserve of oxygen. Myoglobin binds oxygen in a manner similar to hemoglobin, the oxygen-carrying protein found in red blood cells, but it has a higher affinity for oxygen, which allows it to effectively retain oxygen for use during muscle contraction. When muscles are active and demand increases, myoglobin releases the stored oxygen to facilitate aerobic respiration, which is crucial for producing ATP efficiently. This is especially important during intense exercise when the muscles require rapid energy production and may not receive sufficient oxygen from the blood supply alone. In contrast, while creatine phosphate provides quick energy by regenerating ATP from ADP, and ATP is essential for muscle contraction, neither of these directly serves the purpose of oxygen storage. Hemoglobin, while vital for transporting oxygen from the lungs to tissues, is not found in myofibers and does not participate in oxygen storage within the muscle cells. Thus, myoglobin's role is critical in allowing myofibers to have immediate access to oxygen for metabolic processes, especially during high-intensity activities.