Red muscle fibres are heavily dependent on which of the following in order to function properly?
(i) Oxygen concentration
(ii) ATP levels
(iii) Intracellular glucose storage

Options

A. I and II only
B. II and III only
C. III only
D. I, II and III

Answer

To determine the factors that red muscle fibers depend on to function properly, let's analyze the options provided:

1. **Oxygen concentration**: Red muscle fibers, also known as slow-twitch fibers or Type I fibers, are rich in myoglobin, which is a protein that binds oxygen. This high myoglobin content allows these fibers to store oxygen and utilize it for aerobic respiration. Therefore, oxygen concentration is crucial for the proper functioning of red muscle fibers.

2. **ATP levels**: Red muscle fibers are also rich in mitochondria, which are the powerhouses of the cell. These mitochondria produce ATP through aerobic respiration. Since red muscle fibers rely on aerobic metabolism for energy, maintaining high ATP levels is essential for their function.

3. **Intracellular glucose storage**: While glucose is an important energy source, red muscle fibers do not primarily rely on storing glucose. Instead, they utilize fatty acids and oxygen for energy production during prolonged, low-intensity activities. Therefore, intracellular glucose storage is not a significant factor for their proper functioning.

Based on this analysis, the red muscle fibers are heavily dependent on:
- (i) Oxygen concentration
- (ii) ATP levels

Thus, the correct answer is **(i) Oxygen concentration and (ii) ATP levels only**.