Final answer:
Cardiac muscle ensures sufficient oxygen during systole through the presence of a large amount of myoglobin, numerous mitochondria, and plenty of aerobic enzymes, making the answer D. All apply.
Step-by-step explanation:
The cardiac muscle's ability to maintain sufficient oxygen during systole, which is the phase of the heartbeat when the heart muscle contracts and pumps blood, is due to a combination of mechanisms. These include:
- A large amount of myoglobin, which stores oxygen within the muscle cells.
- A high number of mitochondria in the muscle cells, which are essential for aerobic metabolism that produces the necessary ATP for muscle contraction.
- An abundance of aerobic enzymes in the mitochondria that facilitate the use of oxygen for energy production. Therefore, the correct answer to the question is D. All apply, as each of these components plays a role in ensuring the cardiac muscle cells have enough oxygen to function properly during the intense activity of systole.