Question

State three differences between red muscle fiber and white muscle fiber.

Answer 1

Hint: Both red muscle and white muscle fiber are a type of skeletal muscle. One of their key differences lies in the presence or absence of oxygen-binding protein in muscles responsible for their characteristic color.

Complete answer:

Property	Red muscle fiber	White muscle fiber
Definition	These are a type of skeletal muscle which are red in color due to an abundance of myoglobin.	These are a type of skeletal muscle which are white in color due to the lack of myoglobin.
Fatigue	They are not easily fatigued as they can undergo many cycles of aerobic respiration without accumulating lactic acid.	They get fatigued easily as they perform anaerobic respiration and thus the accumulation of lactic acid causes pain and fatigue.
Mitochondria and sarcoplasmic reticulum	They have more mitochondria and less sarcoplasmic reticulum.	White muscle has less number of mitochondria but more number of sarcoplasmic reticulum.

Additional Information: Skeletal muscles are made up of a number of muscular bundles or fascicle which are held together by a layer of connective tissue ‘fascia’. Muscular bundles, in turn, are composed of muscle fiber. Muscle fibers are formed by parallelly arranged myofibrils of myofilaments. Each myofibril has alternate light and dark bands known as I-band and A-band. I-bands or Isotropic bands include only actin and A-band or anisotropic bands include both myosin and actin. Each I- band at its center has a dark membrane known as ‘Z-line’ or ‘Z-disc’.Actin filaments attach at Z-disc by a protein named as ‘alpha-actinin’. The area between the two Z-discs is considered a sarcomere.

Note: Red muscle fiber can be found in the extensor muscle of the back in humans or flight muscles of birds, where high energy demand is required with sustained contraction. White muscle fibers are located in areas that require a faster rate of contraction with short periods as in eyeball muscles.