Correct Option
The correct option is Fewer mitochondria and less myoglobin.
Explanation
Muscle fibres are classified into two main types based on the content of the oxygen-storing pigment myoglobin and the density of mitochondria: Red muscle fibres (aerobic) and White muscle fibres (anaerobic).
Detailed Analysis
- Red Muscle Fibres: These fibres contain a high concentration of myoglobin, giving them a reddish appearance. They possess numerous mitochondria to utilize oxygen for ATP production (aerobic respiration). They are adapted for slow, sustained contractions and are resistant to fatigue.
- White Muscle Fibres: These fibres contain very little myoglobin, resulting in a pale or white appearance. They have fewer mitochondria compared to red fibres and rely primarily on anaerobic respiration (glycolysis) for energy. However, they have a highly developed sarcoplasmic reticulum, enabling rapid calcium release.
Option Analysis
- Fewer mitochondria and less myoglobin is Correct: White muscle fibres are characterized by a low quantity of myoglobin and fewer mitochondria.
- More mitochondria and more myoglobin is Incorrect: High mitochondrial density and high myoglobin content are characteristics of red muscle fibres.
- High aerobic capacity is Incorrect: High aerobic capacity is a feature of red muscle fibres due to their ability to store oxygen and generate energy via oxidative phosphorylation. White fibres rely on anaerobic metabolism.
- Slow contraction rate is Incorrect: Slow contraction rates are associated with red muscle fibres (slow-twitch). White muscle fibres are known as fast-twitch fibres because they contract rapidly but fatigue quickly.
Key Takeaway: White muscle fibres are fast-twitch fibres adapted for short bursts of intense activity; they are distinguished by low myoglobin content, fewer mitochondria, and a reliance on anaerobic respiration.