Which is not true for red fibres

Options

A. Muscles contain a red coloured oxygen storing pigment
B. Muscles contain plenty of mitochondria
C. They are also called aerobic muscles
D. Amount of sarcoplasmic reticulum is high.

Answer

To determine which statement is not true for red fibers, let's analyze each option step by step.

### Step 1: Understand Red Fibers
Red fibers, also known as slow-twitch muscle fibers, are characterized by their high myoglobin content, which gives them a red color. They are primarily involved in endurance activities.

### Step 2: Analyze Each Option
1. **Muscle contains a red color oxygen-storing pigment.**
- This statement is true. Red fibers contain myoglobin, which stores oxygen and gives the fibers their red color.

2. **Muscle contains plenty of mitochondria.**
- This statement is also true. Red fibers have a high number of mitochondria, which are essential for aerobic respiration and energy production.

3. **They are also called aerobic muscles.**
- This statement is true as well. Due to their high mitochondrial content and reliance on aerobic metabolism, red fibers are often referred to as aerobic muscles.

4. **Amount of sarcoplasmic reticulum is high.**
- This statement is not true. Red fibers typically have a lower amount of sarcoplasmic reticulum compared to white fibers. The sarcoplasmic reticulum is responsible for calcium storage and release, which is more prominent in fast-twitch fibers.

### Conclusion
The statement that is not true for red fibers is: **"Amount of sarcoplasmic reticulum is high."**

### Final Answer
The correct option is: **D. Amount of sarcoplasmic reticulum is high.**

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