Q: Which organelle is abundant in white fibers of muscles?  

Answer: A

Muscles contain two types of fibers, red and white. The red fibers are rich in myoglobin, which is a red-colored oxygen-storing protein, and mitochondria, which allow them to generate ATP aerobically and sustain prolonged contractions. Myoglobin is what gives these fibers their characteristic color. On the other hand, the white fibers are rich in sarcoplasmic reticulum, an organelle that plays a critical role in muscle contraction by releasing calcium ions, which trigger the sliding of the myosin and actin filaments. Peroxisomes are involved in lipid metabolism and detoxification, while nuclei are involved in genetic regulation and protein synthesis. However, neither of these organelles is particularly abundant in the white fibers of muscles.

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