Question

Dark bands are
A. A-band
B. B-band
C. I-band
D. Z-line

Answer 1

Hint: A band is one of the cross striations in the striated muscle that comprise myosin filaments and appear dark under the light microscope and light in polarized light. A-bands in muscles are the dark bands that are in areas in which thick myosin filaments are found.

Complete step-by-step answer:
Myofibrils are contractible units within the cell that comprises a day-to-day array of protein myofilaments. Each myofilament moves longitudinally with reference to the muscle cell. There are two kinds: thin bands and thick bands. Thick bands are created from different molecules of a protein known as myosin. The thin bands are created from several molecules of a protein known as actin. The slight actin groups are attached to a Z-circle or Z-line of a versatile protein known as titin. From each Z-line to subsequent may be a unit referred to as the sarcomere. The sarcomere is the tiniest contractile unit within the myofibril. Sarcomeres contract due to the Z-lines moving closer to each other. When the sarcomeres contract, the myofibrils contract. When the myofibrils contract, the muscle cell contracts. And since cells contract, the entire muscle contracts.

In a striated muscle, the myofibrils are assembled into alternative dark and light bands or striations. The dark bands are known as anisotropic bands or A-bands and light bands are known as isotropic bands or I-bands. Consequently, Myofibrils show lightweight and dark bands in striated muscles and cardiac muscles.

Hence the correct answer is A-band.

Note: The striated form of skeletal muscle tissue is a result of the repetitive bands of the proteins myosin and actin that are found along the length of the myofibrils. The light I band, and dark A bands repeat along myofibrils, and the alignment of myofibrils in the cell causes the whole cell to appear banded or striated.