Final answer:
Slow fibers, also known as slow-twitch muscle fibers, have larger fiber diameters, contract for extended periods of time, and contain a large number of mitochondria. They appear dark red due to the presence of myoglobin.
Step-by-step explanation:
Slow-twitch muscle fibers, also known as slow fibers, have a dark red appearance due to the presence of the pigment myoglobin. They have larger fiber diameters compared to fast fibers. Slow fibers contract for extended periods of time, although they generate less tension compared to fast fibers. Lastly, slow fibers contain a large number of mitochondria, which allows them to carry out aerobic metabolism for sustained activity.