A red blood cell has a round structure. A muscle cell has a long, thin structure. Which statement best explains why these two types of cells have different structures

The red balloons have a biconcave disk structure, which is what is worded in the question seems to me a little wrong.

On the other hand, the elongated structure of muscle cells is due to a greater initial length in order to perform muscle contractions in a better way, or to perform their function at sea.

Something very important that the differences is that the red balloon does not have a nucleus (the muscle cell is multinucleated and has more mitochondrial load) and this structure is characteristic for being able to transport gases such as oxygen and disseminate them better in the body.

Explanation:

Red blood cells also have a shorter half-life than muscle cells, they are responsible for traveling throughout the body and renew their hemoglobin component after 120 days in the spleen.

On the other hand it is important to note that both work together when performing physical exercise, one donates oxygen and the other consumes it, considering that the muscle cell has more capacity to withstand hypoxic moments, that is why it supports lactic fermentations in anaerobic processes.

In summary, the red globule has this shape to act as gas transport, and the muscle cell to have a better start in contractile function.