White muscle fibres contain more

Options

A. Sarcoplasmic reticulum
B. Myoglobin
C. Mitochondria
D. Blood supply

Answer

**Step-by-Step Solution:**

1. **Understanding Muscle Fiber Types:**
- Muscle fibers in humans can be categorized into two main types: red muscle fibers and white muscle fibers. Each type has distinct characteristics and functions.

2. **Characteristics of White Muscle Fibers:**
- White muscle fibers are also known as fast-twitch fibers. They are designed for quick bursts of power and speed but fatigue more quickly than red muscle fibers.

3. **Components of Muscle Fibers:**
- The key components that differentiate muscle fibers include:
- Myoglobin: A protein that stores oxygen.
- Mitochondria: Organelles responsible for energy production.
- Sarcoplasmic Reticulum: A specialized form of endoplasmic reticulum that stores calcium ions.
- Blood Supply: The vascular network that delivers oxygen and nutrients to the muscles.

4. **Comparison of Components:**
- Red muscle fibers (slow-twitch) have:
- More myoglobin (which gives them a red color).
- More mitochondria (for sustained energy production).
- A larger blood supply (to support prolonged activity).
- White muscle fibers (fast-twitch) have:
- Less myoglobin (which contributes to their white color).
- Fewer mitochondria (as they rely on anaerobic metabolism).
- Less blood supply (as they do not require as much oxygen for short bursts of activity).
- More sarcoplasmic reticulum (to release calcium ions quickly for rapid contractions).

5. **Conclusion:**
- Therefore, the correct answer to the question "White muscle fibers contain more..." is **sarcoplasmic reticulum**.

**Final Answer:**
- White muscle fibers contain more **sarcoplasmic reticulum**.

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