Chapter 32, Problem 34A

Summary Introduction

Introduction:

There are two types of skeletal muscle fibers:

1. slow-twitch
2. fast-twitch

Slow-twitch muscle fibers give stamina for a longer duration for the activities like marathon running. Fast-twitch muscle fibers give stamina for quick movements like weightlifting.

Answer to Problem 34A

Correct answer:

The correct answer is option (C).

Explanation of Solution

Explanation/justification for the correct answer:

Option (c) they have fewer mitochondria than slow-twitch fibers. They also have a fewer amount of myoglobin proteins than slow-twitch fibers. Slow-twitch fibers synthesize a large amount of energy through anaerobic processes (in the absence of free or combined oxygen).

Explanation for incorrect answer:

Option (a) they contain more myoglobin than slow-twitch fibers is a wrong option as they have lower concentrations of mitochondria and myoglobin compared to slow-twitch fibers, which means they are quicker to fatigue.

Option (b) they are resistant to fatigue is a wrong option as they have lower concentrations of mitochondria and myoglobin compared to slow-twitch fibers, and therefore, they are quicker to fatigue.

Option (d) they require high amounts of oxygen in order to function is a wrong option as they depend on anaerobic respiration to produce ATP molecule, though they are less effective than aerobic respiration. So they don’t have much need for oxygen.

Conclusion

Fast-twitch muscle fibers have fewer mitochondria than slow-twitch fibers.